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AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION
Electronic Newsletter -- #25, Summer 2021-22
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The ASGRG has a home web page at http://www.asgrg.org
Items for this newsletter should be emailed to the editor:
asgrg@hotmail.com
The deadline for the next issue is 30 November, 2022.
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CONTENTS:
* REPORT ON 10TH AUSTRALASIAN CONFERENCE ON GENERAL RELATIVITY AND
GRAVITATION (ACGRG10): Victoria University of Wellington, New Zealand,
10-13 December, 2019
* MINUTES OF THE 11^TH BIENNIAL GENERAL MEETING OF THE ASGRG
held at Victoria University of Wellington, New Zealand, Tuesday 10
December, 2019
* 2020 PRIME MINISTERS PRIZE FOR SCIENCE
awarded to ASGRG members Susan Scott, David Blair, David McClelland and
Peter Veitch
* 11TH AUSTRALASIAN CONFERENCE ON GENERAL RELATIVITY AND GRAVITATION
(ACGRG11): University of Tasmania, Hobart, 2-4 February, 2022
* 12TH BIENNIAL GENERAL MEETING OF THE ASGRG, 3 February 2022
* MEMBERSHIP DETAILS ONLINE at
http://www.asgrg.org/membership/index.php
* FORTHCOMING MEETINGS
* MEMBERS' ABSTRACTS at gr-qc, December 2019 - November 2021
* ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc, December
2019 - November 2021
******************************************************************************
REPORT ON 10TH AUSTRALASIAN CONFERENCE ON GENERAL RELATIVITY AND
GRAVITATION (ACGRG10)
Victoria University of Wellington, New Zealand, 10-13 December, 2019
ACGRG10 was the tenth in the series of biennial conferences run by the
ASGRG. The venue was the Kelburn campus of Victoria University of
Wellington.
Keynote talks were given by Jörg Hennig (solitons and black holes),
Volker Schlue (expanding black hole spacetimes), Maria Eugenia Gabach
Clement (quasilocal quantities in GR), Karl Wette (continuous GWs from
rapidly rotating neutron stars), Krzysztof Bolejko (non-Riemannian
signatures in cosmological data), and Robert Ward (precision measurement
of space-time). In addition, there were another 18 contributed talks on
a range of mostly theoretical topics, covering inflation, cosmic
expansion, wormholes, Hawking radiation, Bianchi models, the Sagnac
effect, modified gravity, neutron stars and black hole perturbation theory.
The winner of the Kerr Prize for the best student talk at ACGRG10 was
Jessica Santiago of Victoria University of Wellington, who spoke on
Thermodynamic equilibrium in General Relativity.
ACGRG10 also included an Education and Outreach session for science
teachers on 13 December, which featured workshop-style presentations by
Shon Boubil, Matt Visser and Jackie Bondell.
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MINUTES OF THE 11TH BIENNIAL GENERAL MEETING OF THE ASGRG
held at Victoria University of Wellington, New Zealand, Tuesday 10
December, 2019
The meeting opened at 4.15 p.m.
Present: Jörg Frauendiener (President), Malcolm Anderson (Secretary),
Susan Scott, David Wiltshire, Karl Wette, Krzysztof Bolejko, Colin
Maclaurin, Woei Chet Lim, Matt Visser, Nikodem Poplawski
Apologies: Todd Oliynyk (Treasurer), Leo Brewin
1. The minutes of the 10th Biennial General Meeting, held at the Gravity
Discovery Centre, Gingin, Western Australia on Monday 27 November, 2017,
were presented to the meeting. Woei Chet Lim moved that the minutes be
accepted, and David Wiltshire seconded. The motion was approved, with
the following corrections:
David Wilshire should be David Wiltshire
Gervais Bay should be Jervis Bay
Barry Barrish (twice) should be Barry Barish
Matters Arising:
Susan Scott mentioned that the ASGRG was not represented by a plenary
speaker at the last AIP Congress. Ray Weiss was invited as a plenary
speaker but pulled out at the last minute, so Susan Scott and Paul Lasky
instead gave a combined plenary talk. Previous plenary speakers in GR at
AIP Congresses have included Bruce Allen, Steve Carlip, Gary Horowitz
and Barry Barish. Jörg promised to submit names of potential plenary
speakers for the next AIP Congress (in Adelaide in December 2020) early
next year.
2. President's Report: Jörg Frauendiener informed the meeting that
(i) The OzGrav Centre [the ARC Centre of Excellence for gravitational
wave discovery, hosted by Swinburne University] is up and running.
(ii) David Wiltshire, Richard Easther and Jenny Adams have submitted a
proposal for a New Zealand Centre of Excellence in Astrophysics, which
if funded will be a network for planetary and space science with 16
principal investigators, costing $5.5 million a year for 8 years. The
proposed name for the project is the Kerr-Tinsley Centre [Beatrice
Tinsley was the first female professor of astrophysics at Yale
University].
(iii) He [Jörg] delivered reports to the AIP Council Meetings in 2018
and 2019, as ASGRG is a cognate society of the Australian Institute of
Physics. ASGRG members are eligible for a fee reduction if they wish to
join the ISGRG. The general advice of the AIP was that the ASGRG should
remove the option of lifetime membership, which was restricting the
income of the society.
3. Treasurer's Report: The Treasurer, Todd Oliynyk, was unable to attend
the BGM and sent his apologies. He reported by email that the Society's
current account contained $10,702 and there was another $5,305.75 in
Paypal. The net balance of funds was therefore $16,009.75.
4. Auditor's Report: No auditors report was available at the BGM.
5. Appointment of Auditor for the next session: Malcolm Anderson would
ask John Schutz if he was willing to remain the Auditor of the Society's
accounts.
6. Election of officers: The following people were elected officers of
the ASGRG Committee for the 2019-2021 session unopposed:
President: Jörg Frauendiener (nominated: David Wiltshire,
seconded: Susan Scott)
Treasurer: Karl Wette (nominated: Susan Scott, seconded:
David Wiltshire)
Secretary: Malcolm Anderson (nominated: David Wiltshire,
seconded: Jörg Frauendiener)
Officer: Susan Scott (nominated: David Wiltshire,
seconded: Jörg Frauendiener)
Officer: David Wiltshire (nominated: Susan Scott,
seconded: Jörg Frauendiener)
Krzysztof Bolejko was also co-opted as a Committee member.
Karl Wette was appointed as a signatory to all the Societys bank
accounts.
7. Date and venue for ACGRG11: The date of the next Conference was set
for December 2021, but the venue remained undecided. The next Amaldi
meeting would be held in July 2021 at Swinburne University in Melbourne.
One possible venue for ACGRG11 was Hobart. Krzysztof Bolejko would
investigate this. ACGRG12 might be hosted by the ANU in December 2023.
8. Other business
There will be a Summer School in Mathematical Relativity in Nelson, New
Zealand in January 2020, organised by the New Zealand Mathematics
Institute. 30 students will attend, including 6 from Australia.
It was agreed that the advertising for ACRGR10 was sent out too late,
and an effort should be made to advertise ACGRG11 much earlier.
It was agreed to keep the fees for membership of the ASGRG unchanged,
namely $40 a year for full membership, $20 a year for student or unwaged
membership, and $250 for lifetime membership.
The ASGRG website is hosted by Monash University, and there is always a
need for someone who can spare the time to update it regularly. Karl
Wette agreed to look at the website and see if he could take it over.
Susan Scott stated that the ASGRG needs more members from OzGrav, and
should actively try to recruit some.
The meeting closed at 5.35 pm.
******************************************************************************
2020 PRIME MINISTERS PRIZE FOR SCIENCE
On 28 October 2020 the $250,000 Australian Prime Ministers Prize for
Science was awarded jointly to David Blair (UWA), David McClelland
(ANU), Susan Scott (ANU) and Peter Veitch (Adelaide) for their work on
gravitational wave astronomy, particularly their contributions to the
first direct detection by LIGO of gravitational waves in 2015. All four
are members of ASGRG.
For more information about the Prize and the scientific contributions of
the recipients, see
pmc.gov.au/news-centre/government/2020-prime-ministers-prizes-science
******************************************************************************
11TH AUSTRALASIAN CONFERENCE ON GENERAL RELATIVITY AND GRAVITATION
(ACGRG11)
University of Tasmania, Hobart, 2-4 February, 2022
ACGRG11 is the eleventh in a series of biennial conferences run by the
ASGRG with the aim of bringing together researchers from around the
world to discuss all aspects of General Relativity, Cosmology and
Relativistic Astrophysics including theory and experiment. The programme
will include both experimental and theoretical plenary sessions, with
invited speakers Vaishali Adya (ANU), Dan Brown (Adelaide), Hayley
Macpherson (Cambridge), Meg Millhouse (Melbourne), Roger Penrose
(Oxford), Ryan Shannon (Swinburne), Rory Smith (Monash), Chris Stevens
(Canterbury) and Magdalena Zych (UQ).
ACGRG11 will be hosted by the University of Tasmania from 2 to 4
February, 2022, and is open to anyone with an interest in general
relativity. Attendance is possible both in person and via zoom.
In addition, Roger Penrose will give a Public Talk (remotely) from 8 to
9 pm on Wednesday 2 February.
Local Organising Committee: Krzysztof Bolejko, Earl Lester, Ben Whale,
Karelle Siellez
Scientific Organising Committee: Joerg Frauendiener (Otago), Carl Blair
(UWA), David Wiltshire (Canterbury), Susan Scott (ANU), Cullan Howlett
(UQ), Jade Powell (Swinburne), Malcolm Anderson (Brunei), Eric Thrane
(Monash), Karl Wette (ANU)
For further details, visit the conference website at asgrg2021.org/home
******************************************************************************
12TH BIENNIAL GENERAL MEETING OF THE ASGRG
The 2022 Biennial General Meeting of the ASGRG will be held in
conjunction with ACGRG11, at 5 pm on Thursday 3 February 2022.
All ASGRG Executive Committee positions will be filled by election at
the BGM. The outgoing Executive Committee members are:
President Jörg Frauendiener
Treasurer - Karl Wette
Secretary - Malcolm Anderson
Officer - Susan Scott
Officer - David Wiltshire
Co-Opted committee member: Krzysztof Bolejko
******************************************************************************
MEMBERSHIP DETAILS ONLINE:
ASGRG members are invited to renew their subscriptions by visiting the
Membership web page at:
http://www.asgrg.org/membership/index.php
Membership is open to anyone interested in General Relativity.
Post-graduate students and early career researchers are particularly
encouraged to apply.
The annual subscription is A$40 (A$20 for students and retirees). Life
membership is available for a one-off payment of A$250.
Members of the Australian Institute of Physics (AIP) are entitled to a
10% discount on all memberships.
******************************************************************************
FORTHCOMING MEETINGS
January 19-24, 2022: Nordic Winter School on Particle Physics
and Cosmology
Thon Hotel Skeikampen
Svingvoll, Norway
http://indico.nbi.ku.dk/event/1324
February 14-18, 2022: SIGRAV International School 2022 on
Cosmology: from Theory to Observation
Italian Society of
General Relativity and Gravitation (online)
http://agenda.infn.it/event/28785
February 14-18, 2022: Gravity The Next Generation
Yukawa Institute for
Theoretical Physics, Kyoto University
Kyoto, Japan
http://www2.yukawa.kyoto-u.ac.jp/~gc2022/YKIS/index.php
February 21-23, 2022: 12^th Central European Relativity Seminar
Budapest, Hungary
http://univie.ac.at/cers/cers12/undex.html
March 14-25, 2022: Theoretical Aspects of Astroparticle
Physics, Cosmology and Gravitation
Galileo Galilei
Institute for Theoretical Physics
Arcetri, Florence, Italy
http://agenda.infn.it/event/28760
April 25-28, 2022: Gravitational Wave and Multimessenger
Astronomy
Physikzentrum Bad Honnef
Hannover, Germany
http://we-heraeus-stiftung.de/veranstaltungen/gravitational-wave-and-multimessenger-astronomy/main/
May 1-7, 2022: Hot Topics in Modern Cosmology
Institut dEtudes
Scientifiques de Cargese
Cargese, France
http://cpt.univ-mrs.fr/~cosmo/SW_2022/index.php
May 19-21, 2022: ICASU Inaugural Conference
Illinois Center for
Advanced Studies of the Universe
University of Illinois
Urbana-Champaign
http://icasu.illinois.edu/inaugural-conference
May 30-June 3, 2022: Informational Architecture of Spacetime
Workshop
Okinawa Institute of
Science and Technology
Okinawa, Japan
http://groups.oist.jp/iasw
June 27-July 1, 2022: Metric-Affine Frameworks for Gravity 2022
Institute of Physics,
University of Tartu
Tartu, Estonia
http://geomgrav.fi.ut.ee/conf/maffgrav2022/
July 3-8, 2022: 23^rd International Conference on
General Relativity and Gravitation (GR23)
Institute of Theoretical
Physics, Chinese Academy of Sciences
Beijing, China
http://gr23beijing.com
July 21-23, 2022: Global Structure in Semi-Classical Gravity
Munich Centre for
Mathematical Philosophy, LMU
Munich, Germany
http://mcmp.philosophie.uni-muenchen.de/events/workshops/container/scg2022/index.html
July 25-29, 2022: Frontiers in Numerical Relativity
TPI, FSU
Jena, Germany
http://indico.nbi.ku.dk/event/1324
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MEMBERS' ABSTRACTS at gr-qc, December 2019 - November 2021
We list here all new abstracts that we are aware of that have been
submitted by our members to gr-qc, or which are cross-linked at gr-qc.
(We have not searched for abstracts on other Cornell University archives
which are not cross-linked to gr-qc.) If you do not send your papers to
gr-qc but would like to have them noted in the newsletters, please send
them to the Editor.
Note that the 208 papers listed here and in the LIGO section represent
1.69% of the 12273 papers posted or cross-linked to gr-qc between
December 2019 and November 2021.
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arXiv:2012.15479 gr-qc astro-ph.SR
*Algorithms for Generating All Static Spherically Symmetric
(An)isotropic Fluid Solutions of Einstein's Equations *
*Authors*: M M Akbar, R Solanki
Abstract: We study the Einstein equations of the static spherically
symmetric anisotropic fluid system in curvature coordinates to find
algorithms that generate all solutions and all solutions that are
regular at the center. All possible combinations of input functions from
the set of four functions that characterize the anisotropic system are
considered and all equivalent conditions for central regularity are
determined (for both isotropic and anisotropic systems). We provide the
first regularity analysis of the known algorithm that uses the potential
function and anisotropy as inputs. For three other choices of input
function pairs (any two of the potential function, density, or radial
pressure), a remarkably straightforward algorithm follows, which is very
efficient in generating regular anisotropic solutions. This is because
the equivalency of the three pairs in this algorithm arises precisely
from the same algebraic relation that made the different equivalent sets
of regularity conditions possible. In addition, the choice of functions
makes this algorithm very suitable for finding particular solutions that
admit other desirable physical properties; we construct three examples.
This algorithm does not admit an isotropic limit although all isotropic
solutions are produced as part of the anisotropic system. The remaining
two choices of input function pairs (anisotropy with the radial pressure
or density) lead to the old barriers one encounters in the isotropic
system: Riccati and Abel equations. However, with any solution generated
by the new and existing algorithms, one can now construct the general
solution of the corresponding Riccati equation to obtain a one-parameter
family of geometries for each input solution. We discuss the regularity
of the resulting solutions.
----------------------------------------------------------------
arXiv:2108.13489 gr-qc
*Generating Spherically Symmetric Static Anisotropic Fluid Solutions of
Einstein's Equations from Hydrostatic Equilibrium *
*Authors*: M M Akbar, R Solanki
Abstract: For static fluid spheres, the condition of hydrostatic
equilibrium is given by the generalized Tolman--Oppenheimer--Volkoff
(TOV) equation, a Riccati equation in the radial pressure. For a perfect
fluid source, it is known that finding a new solution from an existing
solution requires solving a Bernoulli equation, if the density profile
is kept the same. In this paper, we consider maps between static
(an)isotropic fluid spheres with the same (arbitrary) density profile
and present solution-generating techniques to find new solutions from
existing ones. The maps, in general, require solving an associated
Riccati equation, which, unlike the Bernoulli equation, cannot be solved
by quadrature. In any case, it can be shown that the output solution is
not, in general, regular for a given regular input solution. However, if
pressure anisotropy is kept the same, the new solution is both regular
and can be found by solving a Bernoulli equation. We give a few examples
where the generalized TOV equation, under algebraic constraints, can be
converted into a Bernoulli equation and thus, solved exactly. We discuss
the physical significance of these Bernoulli equations. Since the
density profile remains the same in our approach, the spatial line
element is identical for all solutions, which facilitates direct
comparison between various equilibrium configurations using fluid
variables as functions of the radial coordinate. Finally, combining with
the previous study on generation algorithms, we show how this study
leads us to a new three-parameter family of exact solutions that satisfy
all desirable physical conditions.
----------------------------------------------------------------
arXiv:2108.05169 quant-ph gr-qc
*Relativistic Bohmian trajectories of photons via weak measurements *
*Authors*: Joshua Foo, Estelle Asmodelle, Austin P. Lund, Timothy C. Ralph
Abstract: Bohmian mechanics is a nonlocal hidden-variable interpretation
of quantum theory which predicts that particles follow deterministic
trajectories in spacetime. Historically, the study of Bohmian
trajectories has been restricted to nonrelativistic regimes due to the
widely held belief that the theory is incompatible with special
relativity. Here we derive expressions for the relativistic velocity and
spacetime trajectories of photons in a Michelson-Sagnac-type
interferometer. The trajectories satisfy quantum-mechanical continuity
and the relativistic velocity addition rule. Our new velocity equation
is operationally defined in terms of weak measurements of momentum and
energy. We finally propose a modified Alcubierre metric which could give
rise to these trajectories within the paradigm of general relativity.
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arXiv:2003.00477 gr-qc astro-ph.HE hep-th
*Shadow and Quasinormal Modes of a Rotating Loop Quantum Black Hole *
*Authors*: Cheng Liu, Tao Zhu, Qiang Wu, Kimet Jusufi, Mubasher Jamil,
Mustapha Azreg-Aïnou, Anzhong Wang
Abstract: In this paper, we construct an effective rotating loop quantum
black hole (LQBH) solution, starting from the spherical symmetric LQBH
by applying the Newman-Janis algorithm modified by Azreg-Aïnou's
non-complexification procedure, and study the effects of loop quantum
gravity { (LQG) on its shadow}. Given the rotating {LQBH}, we discuss
its horizon, ergosurface, and regularity {as} r0. Depending on the
values of the specific angular momentum a and the polymeric function P
arising from {LQG}, we {find} that the rotating solution we obtained can
represent a regular black hole, a regular extreme black hole, or a
regular spacetime {without horizon (a non-black-hole solution)}. We also
{study} the effects of {LQG} and rotation, and {show} that, in addition
to the specific angular momentum, the polymeric function {also} causes
deformations in the size and shape of the black hole shadow.
Interestingly, for a given value of a and inclination angle _0 , the
apparent size of the shadow monotonically decreases, and the shadow gets
more distorted with increasing P. We also {consider the effects of P on
the deviations from the circularity of the shadow, and find} that the
deviation from circularity increases with increasing P for fixed values
of a and 0. Additionally, we explore the observational implications of
P in comparison with the latest Event Horizon Telescope (EHT)
observation of the supermassive black hole, M87. The connection between
the shadow radius and quasinormal modes in the eikonal limit as well as
{the} deflection of massive particles are also considered. Less
Journal reference: Phys. Rev. D 101, 084001 (2020); Phys.Rev.D 103
(2021) 8, 089902 (erratum)
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arXiv:2004.02602 gr-qc astro-ph.HE hep-th
*Orbital mechanics and quasiperiodic oscillation resonances of black
holes in Einstein-Æther theory *
*Authors*: Mustapha Azreg-Aïnou, Zihang Chen, Bojun Deng, Mubasher
Jamil, Tao Zhu, Qiang Wu, Yen-Kheng Lim
Abstract: In this paper, we study the motion of test particles around
two exact charged black-hole solutions in Einstein-Æther theory.
Specifically, we first consider the quasi-periodic oscillations (QPOs)
and their resonances generated by the particle moving in the
Einstein-Æther black hole and then turn to study the periodic orbits of
the massive particles. For QPOs, we drop the usually adopted assumptions
_U =_ , _L =_r , and _U /_L =3/2 with _U (_L ) and _r (_ )
being the upper (lower) frequency of QPOs and radial (vertical)
epicyclic frequency of the orbiting particles, respectively. Instead, we
put-forward a new working ansatz for which the Keplerian radius is much
closer to that of the innermost stable circular orbit and explore in
detail the effects of the æther field on the frequencies of QPOs. We
then realize good curves for the frequencies of QPOs, which fit to data
of three microquasars very well by ignoring any effects of rotation and
magnetic fields. The innermost stable circular orbits (isco) of timelike
particles are also analyzed and we find the isco radius increases with
increasing c_13 for the first type black hole while decreases with
increasing c_14 for the second one. We also obtain several periodic
orbits and find that they share similar taxonomy schemes as the periodic
equatorial orbits in the Schwarzschild/Kerr metrics, in addition to
exact solutions for certain choices of the Einstein-Æther parameters.
The equations for null geodesics are also briefly considered, where we
study circular photon orbits and bending angles for gravitational lensing.
Journal reference: Phys. Rev. D 102, 044028 (2020)
----------------------------------------------------------------
arXiv:2005.00184 gr-qc
*X-ray reflection spectroscopy with Kaluza-Klein black holes *
*Authors*: Jiachen Zhu, Askar B. Abdikamalov, Dimitry Ayzenberg,
Mustapha Azreg-Ainou, Cosimo Bambi, Mubasher Jamil, Sourabh Nampalliwar,
Ashutosh Tripathi, Menglei Zhou
Abstract: Kaluza-Klein theory is a popular alternative theory of
gravity, with both non-rotating and rotating black hole solutions known.
This allows for the possibility that the theory could be observationally
tested. We present a model which calculates the reflection spectrum of a
black hole accretion disk system, where the black hole is described by a
rotating solution of the Kaluza-Klein theory. We also use this model to
analyze X-ray data from the stella-mass black hole in GRS 1915+105 and
provide constraints on the free parameters of the Kaluza-Klein black holes.
Journal reference: Eur. Phys. J. C (2020) 80:622
----------------------------------------------------------------
arXiv:2007.11023 gr-qc astro-ph.CO math-ph
*Dynamical and static solutions to R=0-scalar-tensor theory *
*Authors*: Mustapha Azreg-Aïnou
Abstract: We consider the most cosmologically interesting and relevant
case of scalar-tensor theory (STT) and derive new normal and phantom,
dynamical and static, solutions. We determine the Bianchi I Kasner
exponents and show that the dynamical solutions are heteroclinic orbits
connecting two singularities. Approaching the singularities, a purely
transverse expansion (no radial expansion or collapse) may occur.
Journal reference: EPL, vol. 130 (2020) 60003
----------------------------------------------------------------
arXiv:2008.08450 gr-qc
*Quasinormal modes, quasiperiodic oscillations and shadow of rotating
regular black holes in non-minimally coupled Einstein-Yang-Mills theory *
*Authors*: Kimet Jusufi, Mustapha Azreg-Aïnou, Mubasher Jamil, Shao-Wen
Wei, Qiang Wu, Anzhong Wang
Abstract: In this paper we obtain an effective metric describing a
regular and rotating magnetic black hole (BH) solution with a Yang-Mills
electromagnetic source in Einstein-Yang-Mills (EYM) theory using the
Newman--Janis algorithm via the non-complexification radial coordinate
procedure. We then study the BH shadow and the quasinormal modes (QNMs)
for massless scalar and electromagnetic fields and the quasiperiodic
oscillations (QPOs). To this end, we also study the embedding diagram
for the rotating EYM BH. The energy conditions, shadow curvature radius,
topology and the dynamical evolution of scalar and electromagnetic
perturbations using the time domain integration method are investigated.
We show that the shadow radius decreases by increasing the magnetic
charge, while the real part of QNMs of scalar and electromagnetic fields
increases by increasing the magnetic charge. This result is consistent
with the inverse relation between the shadow radius and the real part of
QNMs. In addition, we have studied observational constraints on the EYM
parameter via frequency analysis of QPOs and the EHT data of shadow
cast by the M87 central black hole. We also find that the decaying rate
of the EYM BH is slower than that of the neutral and ends up with a
tail. We argue that the rotating EYM black hole can be distinguished
from the Kerr-Newman black hole with a magnetic charge based on the
difference between the angular diameters of their shadows.
Journal reference: Phys. Rev. D 103, 024013 (2021).
----------------------------------------------------------------
arXiv:2008.09115 gr-qc
*Constraining the Generalized Uncertainty Principle Through Black Hole
Shadow and Quasiperiodic Oscillations *
*Authors*: Kimet Jusufi, Mustapha Azreg-Aïnou, Mubasher Jamil, Tao Zhu
Abstract: In this paper we study the effect of the Generalized
Uncertainty Principle (GUP) on the shadow of GUP-modified Kerr black
hole and the correspondence between the shadow radius and the real part
of the quasinormal modes (QNMs). We find that the shadow curvature
radius of the GUP-modfied Kerr black hole is bigger compared to the Kerr
vacuum solution and increases linearly monotonically with the increase
of the GUP parameter. We then investigate the characteristic points of
intrinsic curvature of the shadow from a topological point of view to
calculate the the angular size for these curvature radii of the shadow.
To this end, we have used the EHT data for the M87* black hole to
constrain the upper limits of the GUP parameter red and our result is
<10^95 . Finally, we have explored the connection between the shadow
radius and the scalar/electromagnetic/gravitational QNMs. The
GUP-modified Kerr black hole is also used to provide perfect curve
fitting of the particle oscillation upper and lower frequencies to the
observed frequencies for three microquasars and to restrict the values
of the correction parameter in the metric of the modified black hole to
very reasonable bound <10^77 .
----------------------------------------------------------------
arXiv:2010.09698 gr-qc math-ph
*On "Rotating charged AdS solutions in quadratic f(T) gravity": New
rotating solutions *
*Authors*: Mustapha Azreg-Aïnou
Abstract: We show that there are two or more procedures to generalize
the known four-dimensional transformation, aiming to generate
cylindrically rotating charged exact solutions, to higher dimensional
spacetimes . In the one procedure, presented in Eur. Phys. J. C (2019)
\textbf{79}:668, one uses a non-trivial, non-diagonal, Minkowskian
metric ¯_ij to derive complicated rotating solutions. In the other
procedure, discussed in this work, one selects a diagonal Minkowskian
metric _ij to derive much simpler and appealing rotating solutions. We
also show that if (g_ ,_ij ) is a rotating solution then (g¯_
,¯_ij ) is a rotating solution too with similar geometrical properties,
provided ¯_ij and _ij are related by a symmetric matrix R: ¯_ij =_ik
R_kj .
Journal reference: Eur. Phys. J. C 80, 998 (2020)
----------------------------------------------------------------
arXiv:2011.02276 gr-qc astro-ph.HE hep-th
*Shadow, quasinormal modes and quasiperiodic oscillations of rotating
Kaluza-Klein black holes *
*Authors*: M. Ghasemi-Nodehi, Mustapha Azreg-Aïnou, Kimet Jusufi,
Mubasher Jamil
Abstract: In this paper we study the shadow of rotating Kaluza-Klein
(KK) black holes and the connection between the shadow radius and the
real part of quasi-normal modes (QNMs) in the eiokonal limit. In
addition we have explored the quasi-periodic oscillations (QPOs) in the
rotating KK black hole.
Journal reference: Phys. Rev. D 102, 104032 (2020)
----------------------------------------------------------------
arXiv:2012.03431 gr-qc astro-ph.CO
*Rotating cosmological cylindrical wormholes in GR and TEGR sourced by
anisotropic fluids *
*Authors*: Mustapha Azreg-Aïnou
Abstract: Given an anisotropic fluid source, we determine in closed
forms, upon solving the field equations of general relativity (GR) and
teleparallel gravity (TEGR) coupled to a cosmological constant,
cylindrically symmetric four-dimensional cosmological rotating
wormholes, satisfying all local energy conditions, and cosmological
rotating solutions with two axes of symmetry at finite proper distance.
These solutions have the property that their angular velocity is
proportional to the cosmological constant.
Journal reference: Physics of the Dark Universe 32 (2021) 100802
----------------------------------------------------------------
arXiv:2106.08070 gr-qc astro-ph.HE
*Constraining Wormhole Geometries using the Orbit of S2 Star and the
Event Horizon Telescope *
*Authors*: Kimet Jusufi, Saurabh K., Mustapha Azreg-Aïnou, Mubasher
Jamil, Qiang Wu, Cosimo Bambi
Abstract: In this paper we study the possibility of having a wormhole
(WH) as a candidate for the Sgr A^ ^central object and test this idea
by constraining their geometry using the motion of S2 star and the
reconstructed shadow images. In particular, we consider three WH models,
including WHs in Einstein theory, brane-world gravity, and
Einstein-Dirac-Maxwell theory. To this end, we have constrained the WH
throat using the motion of S2 star and shown that the flare out
condition is satisfied. We also consider the accretion of infalling gas
model and study the accretion rate and the intensity of the
electromagnetic radiation as well as the shadow images.
----------------------------------------------------------------
arXiv:2109.08150 gr-qc
*Axion-plasmon or magnetized plasma effect on an observable shadow and
gravitational lensing of a Schwarzschild black hole *
*Authors*: Farruh Atamurotov, Kimet Jusufi, Mubasher Jamil, Ahmadjon
Abdujabbarov, Mustapha Azreg-Aïnou
Abstract: In this paper, we study the influence of the axion-plasmon, as
proposed in (Phys. Rev. Lett. 120, 181803 (2018)) on the optical
properties of the Schwarzschild black hole. Our aim is to provide a test
to detect the effects of a fixed axion background using black holes. To
accomplish our goal, we explore the effect of the axion-plasmon coupling
on the motion of photons around the Schwarzschild black hole and check
the possibility of observing those effects upon the black hole shadow,
the gravitational deflection angle, Einstein rings and shadow images
obtained by radially infalling gas on a black hole within a plasma
medium. We find that these quantities are indeed affected by the
axion-plasmon coupling parameters which consequently generalize some of
the well-known results in the literature. It is shown that the size of
the black hole shadow decreases with increasing axion-plasmon if
observed from sufficiently large distance.
Journal reference: Physical Review D 104, 064053 (2021)
----------------------------------------------------------------
arXiv:2110.07258 gr-qc astro-ph.CO hep-th
*Constraints on Barrow entropy from M87* and S2 star observations *
Authors: Kimet Jusufi, Mustapha Azreg-Aïnou, Mubasher Jamil, Emmanuel N.
Saridakis
Abstract: We use data from M87* central black hole shadow, as well as
from the S2 star observations, in order to extract constraints on Barrow
entropy. The latter is a modified entropy arising from
quantum-gravitational effects on the black hole horizon, quantified by
the new parameter . Such a change in entropy leads to a change in
temperature, as well as to the properties of the black hole and its
shadow. We investigate the photon sphere and the shadow of a black hole
with Barrow entropy, and assuming a simple model for infalling and
radiating gas we estimate the corresponding intensity. Furthermore, we
use the radius in order to extract the real part of the quasinormal
modes, and for completeness we investigate the spherical accretion of
matter onto the black hole, focusing on isothermal and polytropic test
fluids. We extract the allowed parameter region, and by applying a
Monte-Carlo-Markov Chains analysis we find that 0.0036^+0.0792
_0.0145 . Hence, our results place the upper bound 0.0828 at 1, a
constraint that is less strong than the Big Bang Nucleosynthesis one,
but significantly stronger than the late-time cosmological constraints.
----------------------------------------------------------------
arXiv:1912.05305 gr-qc
*LRS Bianchi I model with perfect fluid equation of state *
*Authors*: Vijay Singh, Aroonkumar Beesham
Abstract: The general solution of the field equations in LRS Bianchi-I
space-time with perfect fluid equation-of-state (EoS) is presented. The
models filled with dust, vacuum energy, Zel'dovich matter and disordered
radiation are studied in detail. A unified and systematic treatment of
the solutions is presented, and some new solutions are found. The dust,
stiff matter and disordered radiation models describe only a decelerated
universe, whereas the vacuum energy model exhibits a transition from a
decelerated to an accelerated phase.
Journal reference: International Journal of Modern Physics D, Vol. 28,
Page 1950056 (2019)
----------------------------------------------------------------
arXiv:1912.05850 gr-qc
*LRS Bianchi I model with constant deceleration parameter *
*Authors*: Vijay Singh, Aroonkumar Beesham
Abstract: An LRS Bianchi I model is considered with constant
deceleration parameter, q=1, where 0 is a constant. The physical and
kinematical behaviour of the models for =0 and 0 is studied in
detail. The model with =0 describes late time acceleration, but eternal
inflation demands a violation of the NEC and WEC. The acceleration is
caused by phantom matter which approaches a cosmological constant at
late times. The solutions with a scalar field also show that the model
is compatible with a phantom field only. A comparison with the
observational outcomes indicates that the universe has entered into the
present accelerating phase in recent past somewhere between 0.2z0.5.
The model obeys the "cosmic no hair conjecture". The models with 0<<1
describe late time acceleration driven by quintessence dark energy. A
violation of the NEC and WEC is required to accommodate the early
inflationary epoch caused by phantom matter. The models with 1<<3
describe decelerating phases which are usually occur in the presence of
dust or radiation. These models are also found anisotropic at early
times and attain isotropy at late times. The model for =3 represents a
stiff matter era which also has shear at early stages and becomes shear
free at late times, but it evolves with an insignificant ceaseless
anisotropy. The models with >3 violate the DEC and the corresponding
scalar field models have negative potential which is physically
unrealistic.
Journal reference: General Relativity and Gravitation (2019)
----------------------------------------------------------------
arXiv:2002.08654 gr-qc
*Plane symmetric model with constant deceleration parameter *
*Authors*: Vijay Singh, Aroonkumar Beesham
Abstract: A plane symmetric Bianchi I model is considered with constant
deceleration parameter, q=1, where 0. The model with =0 violates
the NEC throughout the evolution, and hence provides a physically
unrealistic scenario. The model with 0 obeys the NEC and WEC at late
times, which shows that the models in this case can render a physical
realistic cosmological scenario, though for a restricted period of time.
It is also shown that the physical and kinematical behaviour of both
models remain similar to an LRS Bianchi I model.
----------------------------------------------------------------
arXiv:2003.04602 gr-qc
*LRS Bianchi I model with constant expansion rate in f(R,T) gravity *
*Authors*: Vijay Singh, Aroonkumar Beesham
Abstract: An LRS Bianchi-I space-time model is studied with constant
Hubble parameter in f(R,T)=R+2T gravity. Although a single (primary)
matter source is considered, an additional matter appears due to the
coupling between matter and f(R,T) gravity. The constraints are obtained
for a realistic cosmological scenario, i.e., one obeying the null and
weak energy conditions. The solutions are also extended to the case of a
scalar field (normal or phantom) model, and it is found that the model
is consistent with a phantom scalar field only. The coupled matter also
acts as phantom matter. The study shows that if one expects an
accelerating universe from an anisotropic model, then the solutions
become physically relevant only at late times when the universe enters
into an accelerated phase. Placing some observational bounds on the
present equation of state of dark energy, _0 , the behavior of (z) is
depicted, which shows that the phantom field has started dominating very
recently, somewhere between 0.2z0.5.
Journal reference: Astrophysics and Space Science, Vol 365 Page 125 (2020)
----------------------------------------------------------------
arXiv:2003.08665 gr-qc
*Plane symmetric model in f(R,T) gravity *
*Authors*: Vijay Singh, Aroonkumar Beesham
Abstract: A plane symmetric Bianchi-I model is explored in f(R,T)
gravity, where R is the Ricci scalar and T is the trace of
energy-momentum tensor. The solutions are obtained with the
consideration of a specific Hubble parameter which yields a constant
deceleration parameter. The various evolutionary phases are identified
under the constraints obtained for physically viable cosmological
scenarios. Although a single (primary) matter source is taken, due to
the coupling between matter and f(R,T) gravity, an additional matter
source appears, which mimics a perfect fluid or exotic matter. The
solutions are also extended to the case of a scalar field model. The
kinematical behavior of the model remains independent of f(R,T) gravity.
The physical behavior of the effective matter also remains the same as
in general relativity. It is found that f(R,T) gravity can be a good
alternative to the hypothetical candidates of dark energy to describe
the present accelerating expansion of the universe.
Journal reference: Eur. Phys. J. Plus 135, 319 (2020)
----------------------------------------------------------------
arXiv:2008.00169 astro-ph.CO gr-qc
*Emergent Universe Scenario in Modified Gauss-Bonnet Gravity *
*Authors*: B. C. Paul, S. D. Maharaj, A. Beesham
Abstract: We present modified Gauss-Bonnet gravity without matter in
four dimensions which accommodates flat emergent universe (EU) obtained
in Einstein's general theory of gravity with a non-linear equation of
state. The EU model is interesting which is free from big-bang
singularity with other observed features of the universe. It is assumed
that the present universe emerged out from a static Einstein universe
phase exists in the infinite past. To obtain a flat EU model we
reconstructed mimetic modified f(G)-gravity (G representing Gauss-Bonnet
terms) without matter. The functional form of f(G)-gravity is determined
which accommodates the early inflation and late accelerating phases
without matter.
----------------------------------------------------------------
arXiv:2106.01757 gr-qc
*LRS Bianchi I model with bulk viscosity in f(R,T) gravity *
*Authors*: S. Jokweni, Vijay Singh, Aroonkumar Beesham
Abstract: Locally-rotationally-symmetric Bianchi type-I viscous and non
-viscous cosmological models are explored in general relativity (GR) and
in f(R,T) gravity. Solutions are obtained by assuming that the expansion
scalar is proportional to the shear scalar which yields a constant value
for the deceleration parameter (q=2). Constraints are obtained by
requiring the physical viability of the solutions. A comparison is made
between the viscous and non-viscous models, and between the models in GR
and in f(R,T) gravity. The metric potentials remain the same in GR and
in f(R,T) gravity. Consequently, the geometrical behavior of the f(R,T)
gravity models remains the same as the models in GR. It is found that
f(R,T) gravity or bulk viscosity does not affect the behavior of
effective matter which acts as a stiff fluid in all models. The
individual fluids have very rich behavior. In one of the viscous models,
the matter either follows a semi-realistic EoS or exhibits a transition
from stiff matter to phantom, depending on the values of the parameter.
In another model, the matter describes radiation, dust, quintessence,
phantom, and the cosmological constant for different values of the
parameter. In general, f(R,T) gravity diminishes the effect of bulk
viscosity.
Journal reference: Gravitation and Cosmology, Vol 27, page 169 (2021)
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arXiv:1912.06305 astro-ph.IM astro-ph.HE gr-qc
*Ground-Based Gravitational-Wave Astronomy in Australia: 2019 White Paper *
*Authors*: Matthew Bailes, David McClelland, Eric Thrane, David Blair,
Jeffrey Cooke, David Coward, Robin Evans, Yeshe Fenner, Duncan Galloway,
Jarrod Hurley, Li Ju, Paul Lasky, Ilya Mandel, Kirk McKenzie, Andrew
Melatos, David Ottaway, Susan Scott, Bram Slagmolen, Peter Veitch,
Linqing Wen, Chunnong Zhao
Abstract: The past four years have seen a scientific revolution through
the birth of a new field: gravitational-wave astronomy. The first
detection of gravitational waves---recognised by the 2017 Nobel Prize in
Physics---provided unprecedented tests of general relativity while
unveiling a previously unknown class of massive black holes, thirty
times more massive than the Sun. The subsequent detection of
gravitational waves from a merging binary neutron star confirmed the
hypothesised connection between binary neutron stars and short gamma-ray
bursts while providing an independent measurement of the expansion of
the Universe. The discovery enabled precision measurement of the speed
of gravity while shedding light on the origin of heavy elements. At the
time of writing, the Laser Interferometer Gravitational-wave Observatory
(LIGO) and its European partner, Virgo, have published the detection of
eleven gravitational-wave events. New, not-yet-published detections are
announced on a nearly weekly basis. This fast-growing catalogue of
gravitational-wave transients is expected to yield insights into a
number of topics, from the equation of state of matter at supra-nuclear
densities to the fate of massive stars. The science potential of 3G
observatories is enormous, enabling measurements of gravitational waves
from the edge of the Universe and precise determination of the neutron
star equation of state. Australia is well-positioned to help develop the
required technology. The Mid-term Review for the Decadal plan for
Australian astronomy 2016-2025 should consider investment in a scoping
study for an Australian Gravitational-Wave Pathfinder that develops and
validates core technologies required for the global 3G detector network.
----------------------------------------------------------------
arXiv:2001.11173 astro-ph.IM gr-qc physics.ins-det
*A Cryogenic Silicon Interferometer for Gravitational-wave Detection *
*Authors*: Rana X Adhikari, Odylio Aguiar, Koji Arai, Bryan Barr,
Riccardo Bassiri, Garilynn Billingsley, Ross Birney, David Blair, Joseph
Briggs, Aidan F Brooks, Daniel D Brown, Huy-Tuong Cao, Marcio
Constancio, Sam Cooper, Thomas Corbitt, Dennis Coyne, Edward Daw,
Johannes Eichholz, Martin Fejer, Andreas Freise, Valery Frolov, Slawomir
Gras, Anna Green, Hartmut Grote, Eric K Gustafson , et al. (86
additional authors not shown)
Abstract: The detection of gravitational waves from compact binary
mergers by LIGO has opened the era of gravitational wave astronomy,
revealing a previously hidden side of the cosmos. To maximize the reach
of the existing LIGO observatory facilities, we have designed a new
instrument that will have 5 times the range of Advanced LIGO, or greater
than 100 times the event rate. Observations with this new instrument
will make possible dramatic steps toward understanding the physics of
the nearby universe, as well as observing the universe out to
cosmological distances by the detection of binary black hole
coalescences. This article presents the instrument design and a
quantitative analysis of the anticipated noise floor.
----------------------------------------------------------------
arXiv:2002.02637 gr-qc astro-ph.IM
*Ground Based Gravitational Wave Astronomy in the Asian Region *
*Authors*: Vaishali Adya, Matthew Bailes, Carl Blair, David Blair,
Johannes Eichholz, Joris van Heijningen, Eric Howell, Li Ju, Paul Lasky,
Andrew Melatos, David Ottaway, Chunnong Zhao
Abstract: The current gravitational wave detectors have identified a
surprising population of heavy stellar mass black holes, and an even
larger population of coalescing neutron stars. The first observations
have led to many dramatic discoveries and the confirmation of general
relativity in very strong gravitational fields. The future of
gravitational wave astronomy looks bright, especially if additional
detectors with greater sensitivity, broader bandwidth, and better global
coverage can be implemented. The first discoveries add impetus to
gravitational wave detectors designed to detect in the nHz, mHz and kHz
frequency bands. This paper reviews the century-long struggle that led
to the recent discoveries, and reports on designs and possibilities for
future detectors. The benefits of future detectors in the Asian region
are discussed, including analysis of the benefits of a detector located
in Australia.
----------------------------------------------------------------
arXiv:2007.03128 astro-ph.HE astro-ph.IM gr-qc
*Neutron Star Extreme Matter Observatory: A kilohertz-band
gravitational-wave detector in the global network *
*Authors*: K. Ackley, V. B. Adya, P. Agrawal, P. Altin, G. Ashton, M.
Bailes, E. Baltinas, A. Barbuio, D. Beniwal, C. Blair, D. Blair, G. N.
Bolingbroke, V. Bossilkov, S. Shachar Boublil, D. D. Brown, B. J.
Burridge, J. Calderon Bustillo, J. Cameron, H. Tuong Cao, J. B. Carlin,
S. Chang, P. Charlton, C. Chatterjee, D. Chattopadhyay, X. Chen , et al.
(139 additional authors not shown)
Abstract: Gravitational waves from coalescing neutron stars encode
information about nuclear matter at extreme densities, inaccessible by
laboratory experiments. The late inspiral is influenced by the presence
of tides, which depend on the neutron star equation of state. Neutron
star mergers are expected to often produce rapidly-rotating remnant
neutron stars that emit gravitational waves. These will provide clues to
the extremely hot post-merger environment. This signature of nuclear
matter in gravitational waves contains most information in the 2-4 kHz
frequency band, which is outside of the most sensitive band of current
detectors. We present the design concept and science case for a neutron
star extreme matter observatory (NEMO): a gravitational-wave
interferometer optimized to study nuclear physics with merging neutron
stars. The concept uses high circulating laser power, quantum squeezing
and a detector topology specifically designed to achieve the
high-frequency sensitivity necessary to probe nuclear matter using
gravitational waves. Above one kHz, the proposed strain sensitivity is
comparable to full third-generation detectors at a fraction of the cost.
Such sensitivity changes expected event rates for detection of
post-merger remnants from approximately one per few decades with two A+
detectors to a few per year, and potentially allows for the first
gravitational-wave observations of supernovae, isolated neutron stars,
and other exotica.
Journal reference: PASA (2020) 37, e047
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arXiv:2003.06528 astro-ph.CO gr-qc
*Cosmological signatures of torsion and how to distinguish torsion from
the dark sector *
*Authors*: Krzysztof Bolejko, Matteo Cinus, Boudewijn F. Roukema
Abstract: Torsion is a non-Riemannian geometrical extension of general
relativity that allows including the spin of matter and the twisting of
spacetime. Cosmological models with torsion have been considered in the
literature to solve problems of either the very early (high redshift z)
or the present-day Universe. This paper focuses on distinguishable
observational signatures of torsion that could not be otherwise
explained with a scalar field in pseudo-Riemannian geometry. We show
that when torsion is present, the cosmic duality relation between the
angular diameter distance, D_A , and the luminosity distance, D_L , is
broken. We show how the deviation described by the parameter =D_L /[D_A
(1+z)^2 ]1 is linked to torsion and how different forms of torsion lead
to special-case parametrisations of , including _0 z, _0 z/(1+z), and
_0 ln(1+z). We also show that the effects of torsion could be visible
in low-redshift data, inducing biases in supernovae-based H0
measurements. We also show that torsion can impact the
Clarkson-Bassett-Lu (CBL) function C(z)=1+H^2 (DDD2)+HHDD, where D
is the transverse comoving distance. If D is inferred from the
luminosity distance, then, in general non-zero torsion models, C(z)0.
For pseudo-Riemannian geometry, the Friedmann-Lemaitre-Robertson-Walker
(FLRW) metric has C(z)0; thus, measurement of the CBL function could
provide another diagnostic of torsion.
Journal reference: Physics Review D 101 (2020) 104046
----------------------------------------------------------------
arXiv:2105.12933 astro-ph.CO gr-qc
*Exploring the Redshift-Space Peculiar Velocity Field and its Power
Spectrum *
*Authors*: Lawrence Dam, Krzysztof Bolejko, Geraint F. Lewis
Abstract: Redshift-space distortions (RSD) generically affect any
spatially-dependent observable that is mapped using redshift
information. The effect on the observed clustering of galaxies is the
primary example of this. This paper is devoted to another example: the
effect of RSD on the apparent peculiar motions of tracers as inferred
from their positions in redshift space (i.e. the observed distance). Our
theoretical study is motivated by practical considerations, mainly, the
direct estimation of the velocity power spectrum, which is preferably
carried out using the tracer's redshift-space position (so as to avoid
uncertainties in distance measurements). We formulate the redshift-space
velocity field and show that RSD enters as a higher-order effect.
Physically, this effect may be interpreted as a dissipative correction
to the usual perfect-fluid description of dark matter. We show that the
effect on the power spectrum is a damping on relatively large,
quasilinear scales (k>0.01hMpc^1 ), as was observed, though
unexplained, in N-body simulations elsewhere. This paper presents two
power spectrum models for the peculiar velocity field in redshift space,
both of which can be considered velocity analogues of existing
clustering models. In particular, we show that the "Finger-of-God"
effect, while also present in the velocity field, cannot be entirely
blamed for the observed damping in simulations. Our work provides some
of the missing modelling ingredients required for a density--velocity
multi-tracer analysis, which has been proposed for upcoming redshift
surveys.
Journal reference: JCAP09(2021)018
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arXiv:1912.08839 gr-qc
Using Cadabra for tensor computations in General Relativity
*Authors*: Leo Brewin
Abstract: Cadabra is an open access program ideally suited to complex
tensor commutations in General Relativity. Tensor expressions are
written in LaTeX while an enhanced version of Python is used to control
the computations. This tutorial assumes no prior knowledge of Cadabra.
It consists of a series of examples covering a range of topics from
basic syntax such as declarations, functions, program control, component
computations, input and output through to complete computations
including a derivation of two of the BSSN equations from the ADM
equations. Numerous exercises are included along with complete
solutions. All of the source code for the examples, exercises and
solutions are available on GitHub.
----------------------------------------------------------------
arXiv:2009.11516 gr-qc
*Non-aligned Einstein-Maxwell Robinson-Trautman fields of Petrov type D *
*Authors*: Norbert Van den Bergh, John Carminati
Abstract: We discuss Petrov type D Einstein-Maxwell fields in which both
double null eigenvectors of the Weyl tensor are non-aligned with the
eigenvectors of a non-null electromagnetic field and are assumed to be
geodesic, shear-free, diverging and non-twisting. We obtain the general
solution of the Einstein-Maxwell equations under the extra condition
that the complex null vectors of the Weyl canonical tetrad are
hypersurface orthogonal. The corresponding space-times are all
conformally related to a Killing-Yano space and are described by a
5-parameter family of metrics, admitting two commuting Killing vectors
and having the C-metric as a possible vacuum limit.
----------------------------------------------------------------
arXiv:2111.06303 gr-qc
*Comment on "Shear-free barotropic perfect fluids cannot rotate and
expand simultaneously" by R. Goswami and G.F.R. Ellis *
*Authors*: Norbert Van den Bergh, John Carminati
Abstract: We point out an error in a recent paper by Goswami and Ellis.
As a consequence the question of whether shear-free barotropic perfect
fluids (with p+0) can or cannot rotate and expand simultaneously, is
still wide open.
----------------------------------------------------------------
arXiv:1912.08807 gr-qc astro-ph.HE
*Joint search for isolated sources and an unresolved confusion
background in pulsar timing array data *
*Authors*: Bence Bécsy, Neil J. Cornish
Abstract: Supermassive black hole binaries are the most promising source
of gravitational-waves in the frequency band accessible to pulsar timing
arrays. Most of these binaries will be too distant to detect
individually, but together they will form an approximately stochastic
background that can be detected by measuring the correlation pattern
induced between pairs of pulsars. A small number of nearby and
especially massive systems may stand out from this background and be
detected individually. Analyses have previously been developed to search
for stochastic signals and isolated signals separately. Here we present
BayesHopper, an algorithm capable of jointly searching for both signal
components simultaneously using trans-dimensional Bayesian inference.
Our implementation uses the Reversible Jump Markov Chain Monte Carlo
method for sampling the relevant parameter space with changing
dimensionality. We have tested BayesHopper on various simulated
datasets. We find that it gives results consistent with
fixed-dimensional methods when tested on data with a stochastic
background or data with a single binary. For the full problem of
analyzing a dataset with both a background and multiple black hole
binaries, we find two kinds of interactions between the binary and
background components. First, the background effectively increases the
noise level, thus making individual binary signals less significant.
Second, weak binary signals can be absorbed by the background model due
to the natural parsimony of Bayesian inference. Because of its flexible
model structure, we anticipate that BayesHopper will outperform existing
approaches when applied to realistic data sets produced from population
synthesis models.
Journal reference: Bence Becsy and Neil J. Cornish 2020 Class. Quantum
Grav. 37 135011
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arXiv:2001.00595 astro-ph.HE astro-ph.IM gr-qc
*Modeling the uncertainties of solar-system ephemerides for robust
gravitational-wave searches with pulsar timing arrays *
*Authors*: M. Vallisneri, S. R. Taylor, J. Simon, W. M. Folkner, R. S.
Park, C. Cutler, J. A. Ellis, T. J. W. Lazio, S. J. Vigeland, K.
Aggarwal, Z. Arzoumanian, P. T. Baker, A. Brazier, P. R. Brook, S.
Burke-Spolaor, S. Chatterjee, J. M. Cordes, N. J. Cornish, F. Crawford,
H. T. Cromartie, K. Crowter, M. DeCesar, P. B. Demorest, T. Dolch, R. D.
Ferdman , et al. (39 additional authors not shown)
Abstract: The regularity of pulsar emissions becomes apparent once we
reference the pulses' times of arrivals to the inertial rest frame of
the solar system. It follows that errors in the determination of Earth's
position with respect to the solar-system barycenter can appear as a
time-correlated bias in pulsar-timing residual time series, affecting
the searches for low-frequency gravitational waves performed with pulsar
timing arrays. Indeed, recent array datasets yield different
gravitational-wave background upper limits and detection statistics when
analyzed with different solar-system ephemerides. Crucially, the
ephemerides do not generally provide usable error representations. In
this article we describe the motivation, construction, and application
of a physical model of solar-system ephemeris uncertainties, which
focuses on the degrees of freedom (Jupiter's orbital elements) most
relevant to gravitational-wave searches with pulsar timing arrays. This
model, BayesEphem, was used to derive ephemeris-robust results in
NANOGrav's 11-yr stochastic-background search, and it provides a
foundation for future searches by NANOGrav and other consortia. The
analysis and simulations reported here suggest that ephemeris modeling
reduces the gravitational-wave sensitivity of the 11-yr dataset; and
that this degeneracy will vanish with improved ephemerides and with the
longer pulsar timing datasets that will become available in the near future
----------------------------------------------------------------
arXiv:2003.09456 gr-qc
*Reconstructing gravitational wave signals from binary black hole
mergers with minimal assumptions *
*Authors*: Sudarshan Ghonge, Katerina Chatziioannou, James A. Clark,
Tyson Littenberg, Margaret Millhouse, Laura Cadonati, Neil Cornish
Abstract: We present a systematic comparison of the binary black hole
(BBH) signal waveform reconstructed by two independent and complementary
approaches used in LIGO and Virgo source inference: a template-based
analysis, and a morphology-independent analysis. We apply the two
approaches to real events and to two sets of simulated observations made
by adding simulated BBH signals to LIGO and Virgo detector noise. The
first set is representative of the 10 BBH events in the first
Gravitational Wave Transient Catalog (GWTC-1). The second set is
constructed from a population of BBH systems with total mass and signal
strength in the ranges that ground based detectors are typically
sensitive. We find that the reconstruction quality of the GWTC-1 events
is consistent with the results of both sets of simulated signals. We
also demonstrate a simulated case where the presence of a mismodelled
effect in the observed signal, namely higher order modes, can be
identified through the morphology-independent analysis. This study is
relevant for currently progressing and future observational runs by LIGO
and Virgo.
Journal reference: Phys. Rev. D 102, 064056 (2020)
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arXiv:2004.08464 gr-qc astro-ph.HE astro-ph.IM
*Global Analysis of the Gravitational Wave Signal from Galactic Binaries *
*Authors*: Tyson Littenberg, Neil Cornish, Kristen Lackeos, Travis Robson
Abstract: Galactic ultra compact binaries are expected to be the
dominant source of gravitational waves in the milli-Hertz frequency
band. Of the tens of millions of galactic binaries with periods shorter
than an hour, it is estimated that a few tens of thousand will be
resolved by the future Laser Interferometer Space Antenna (LISA). The
unresolved remainder will be the main source of ``noise'' between 1-3
milli-Hertz. Typical galactic binaries are millions of years from
merger, and consequently their signals will persist for the the duration
of the LISA mission. Extracting tens of thousands of overlapping
galactic signals and characterizing the unresolved component is a
central challenge in LISA data analysis, and a key contribution to
arriving at a global solution that simultaneously fits for all signals
in the band. Here we present an end-to-end analysis pipeline for
galactic binaries that uses trans-dimensional Bayesian inference to
develop a time-evolving catalog of sources as data arrive from the LISA
constellation.
Journal reference: Phys. Rev. D 101, 123021 (2020)
----------------------------------------------------------------
arXiv:2005.03610 gr-qc astro-ph.HE
*Black Hole Hunting with LISA *
*Authors*: Neil J. Cornish, Kevin Shuman
Abstract: The Laser Interferometer Space Antenna (LISA) will be able to
detect massive black hole mergers throughout the visible Universe. These
observations will provide unique information about black hole formation
and growth, and the role black holes play in galaxy evolution. Here we
develop several key building blocks for detecting and characterizing
black hole binary mergers with LISA, including fast heterodyned
likelihood evaluations, and efficient stochastic search techniques.
Journal reference: Phys. Rev. D 101, 124008 (2020)
----------------------------------------------------------------
arXiv:2009.00043 gr-qc astro-ph.HE
*Time-Frequency Analysis of Gravitational Wave Data *
*Authors*: Neil J. Cornish
Abstract: Data from gravitational wave detectors are recorded as time
series that include contributions from myriad noise sources in addition
to any gravitational wave signals. When regularly sampled data are
available, such as for ground based and future space based
interferometers, analyses are typically performed in the frequency
domain, where stationary (time invariant) noise processes can be modeled
very efficiently. In reality, detector noise is not stationary due to a
combination of short duration noise transients and longer duration
drifts in the power spectrum. This non-stationarity produces
correlations across samples at different frequencies, obviating the main
advantage of a frequency domain analysis. Here an alternative
time-frequency approach to gravitational wave data analysis is proposed
that uses discrete, orthogonal wavelet wavepackets. The time domain data
is mapped onto a uniform grid of time-frequency pixels. For locally
stationary noise - that is, noise with an adiabatically varying spectrum
- the time-frequency pixels are uncorrelated, which greatly simplifies
the calculation of quantities such as the likelihood. Moreover, the
gravitational wave signals from binary systems can be compactly
represented as a collection of lines in time-frequency space, resulting
in a computational cost for computing waveforms and likelihoods that
scales as the square root of the number of time samples, as opposed to
the linear scaling for time or frequency based analyses. Key to this
approach is having fast methods for computing binary signals directly in
the wavelet domain. Multiple fast transform methods are developed in
detail.
----------------------------------------------------------------
arXiv:2009.04496 astro-ph.HE astro-ph.GA gr-qc
*The NANOGrav 12.5-year Data Set: Search For An Isotropic Stochastic
Gravitational-Wave Background *
*Authors*: Zaven Arzoumanian, Paul T. Baker, Harsha Blumer, Bence Becsy,
Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Shami Chatterjee,
Siyuan Chen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H.
Thankful Cromartie, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch,
Justin A. Ellis, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca,
Nathan Garver-Daniels, Peter A. Gentile, Deborah C. Good, Jeffrey S.
Hazboun, A. Miguel Holgado , et al. (36 additional authors not shown)
Abstract: We search for an isotropic stochastic gravitational-wave
background (GWB) in the 12.5-year pulsar timing data set collected by
the North American Nanohertz Observatory for Gravitational Waves. Our
analysis finds strong evidence of a stochastic process, modeled as a
power-law, with common amplitude and spectral slope across pulsars. The
Bayesian posterior of the amplitude for an f2/3 power-law spectrum,
expressed as the characteristic GW strain, has median 1.92×1015 and
5%--95% quantiles of 1.37--2.67×1015 at a reference frequency of fyr=1
yr1. The Bayes factor in favor of the common-spectrum process versus
independent red-noise processes in each pulsar exceeds 10,000. However,
we find no statistically significant evidence that this process has
quadrupolar spatial correlations, which we would consider necessary to
claim a GWB detection consistent with general relativity. We find that
the process has neither monopolar nor dipolar correlations, which may
arise from, for example, reference clock or solar system ephemeris
systematics, respectively. The amplitude posterior has significant
support above previously reported upper limits; we explain this in terms
of the Bayesian priors assumed for intrinsic pulsar red noise. We
examine potential implications for the supermassive black hole binary
population under the hypothesis that the signal is indeed astrophysical
in nature.
Journal reference: The Astrophysical Journal Letters, Volume 905, Number
2 (2020)
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arXiv:2010.11950 astro-ph.HE astro-ph.GA gr-qc
*Astrophysics Milestones For Pulsar Timing Array Gravitational Wave
Detection *
*Authors*: Nihan S. Pol, Stephen R. Taylor, Luke Zoltan Kelley, Sarah J.
Vigeland, Joseph Simon, Siyuan Chen, Zaven Arzoumanian, Paul T. Baker,
Bence Bécsy, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Shami
Chatterjee, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H.
Thankful Cromartie, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch,
Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Nathan
Garver-Daniels, Deborah C. Good , et al. (27 additional authors not shown)
Abstract: The NANOGrav Collaboration reported strong Bayesian evidence
for a common-spectrum stochastic process in its 12.5-yr pulsar timing
array dataset, with median characteristic strain amplitude at periods of
a year of Ayr=1.92+0.750.55×1015. However, evidence for the
quadrupolar Hellings \& Downs interpulsar correlations, which are
characteristic of gravitational wave signals, was not yet significant.
We emulate and extend the NANOGrav dataset, injecting a wide range of
stochastic gravitational wave background (GWB) signals that encompass a
variety of amplitudes and spectral shapes, and quantify three key
milestones: (I) Given the amplitude measured in the 12.5 yr analysis and
assuming this signal is a GWB, we expect to accumulate robust evidence
of an interpulsar-correlated GWB signal with 15--17 yrs of data, i.e.,
an additional 2--5 yrs from the 12.5 yr dataset; (II) At the initial
detection, we expect a fractional uncertainty of 40% on the power-law
strain spectrum slope, which is sufficient to distinguish a GWB of
supermassive black-hole binary origin from some models predicting more
exotic origins;(III) Similarly, the measured GWB amplitude will have an
uncertainty of 44% upon initial detection, allowing us to arbitrate
between some population models of supermassive black-hole binaries. In
addition, power-law models are distinguishable from those having
low-frequency spectral turnovers once 20~yrs of data are reached. Even
though our study is based on the NANOGrav data, we also derive relations
that allow for a generalization to other pulsar-timing array datasets.
Most notably, by combining the data of individual arrays into the
International Pulsar Timing Array, all of these milestones can be
reached significantly earlier.
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arXiv:2011.01942 gr-qc astro-ph.HE
*Bayesian search for gravitational wave bursts in pulsar timing array data *
*Authors*: Bence Bécsy, Neil J. Cornish
Abstract: The nanohertz frequency band explored by pulsar timing arrays
provides a unique discovery space for gravitational wave signals. In
addition to signals from anticipated sources, such as those from
supermassive black hole binaries, some previously unimagined sources may
emit transient gravitational waves (a.k.a. bursts) with unknown
morphology. Unmodeled transients are not currently searched for in this
frequency band, and they require different techniques from those
currently employed. Possible sources of such gravitational wave bursts
in the nanohertz regime are parabolic encounters of supermassive black
holes, cosmic string cusps and kinks, or other, as-yet-unknown
phenomena. In this paper we present BayesHopperBurst, a Bayesian search
algorithm capable of identifying generic gravitational wave bursts by
modeling both coherent and incoherent transients as a sum of
Morlet-Gabor wavelets. A trans-dimensional Reversible Jump Markov Chain
Monte Carlo sampler is used to select the number of wavelets best
describing the data. We test BayesHopperBurst on various simulated
datasets including different combinations of signals and noise
transients. Its capability to run on real data is demonstrated by
analyzing data of the pulsar B1855+09 from the NANOGrav 9-year dataset.
Based on a simulated dataset resembling the NANOGrav 12.5-year data
release, we predict that at our most sensitive time-frequency location
we will be able to probe gravitational wave bursts with a
root-sum-squared amplitude higher than 5×10^11 Hz^1/2 , which
corresponds to 40Mc^2 emitted in GWs at a fiducial distance of 100 Mpc.
Journal reference: Bence Becsy and Neil J. Cornish 2021 Class. Quantum
Grav. 38 095012
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arXiv:2011.05055 gr-qc
*Spectral separation of the stochastic gravitational-wave background for
LISA: observing both cosmological and astrophysical backgrounds *
*Authors*: Guillaume Boileau, Nelson Christensen, Renate Meyer, Neil J.
Cornish
Abstract: With the goal of attempting to observe a stochastic
gravitational wave background (SGWB) with LISA, the spectral
separability of the cosmological and astrophysical backgrounds is
important to estimate. We attempt to determine the level with which a
cosmological background can be observed given the predicted
astrophysical background level. We predict detectable limits for the
future LISA measurement of the SGWB. Adaptive Markov chain Monte-Carlo
methods are used to produce estimates with the simulated data from the
LISA Data challenge (LDC). We also calculate the Cramer-Rao lower bound
on the variance of the SGWB parameter uncertainties based on the inverse
Fisher Information using the Whittle Likelihood. The estimation of the
parameters is done with the 3 LISA channels A, E, and T. We
simultaneously estimate the noise using a LISA noise model. Assuming the
expected astrophysical background, a cosmological background energy
density of around GW,Cosmo1×10^12 to 1×10^13 can be detected by LISA.
Journal reference: Phys. Rev. D 103, 103529 (2021)
----------------------------------------------------------------
arXiv:2011.09494 gr-qc astro-ph.HE
*The BayesWave analysis pipeline in the era of gravitational wave
observations *
*Authors*: Neil J. Cornish, Tyson B. Littenberg, Bence Bécsy, Katerina
Chatziioannou, James A. Clark, Sudarshan Ghonge, Margaret Millhouse
Abstract: We describe updates and improvements to the BayesWave
gravitational wave transient analysis pipeline, and provide examples of
how the algorithm is used to analyze data from ground-based
gravitational wave detectors. BayesWave models gravitational wave
signals in a morphology-independent manner through a sum of frame
functions, such as Morlet-Gabor wavelets or chirplets. BayesWave models
the instrument noise using a combination of a parametrized Gaussian
noise component and non-stationary and non-Gaussian noise transients.
Both the signal model and noise model employ trans-dimensional sampling,
with the complexity of the model adapting to the requirements of the
data. The flexibility of the algorithm makes it suitable for a variety
of analyses, including reconstructing generic unmodeled signals; cross
checks against modeled analyses for compact binaries; as well as
separating coherent signals from incoherent instrumental noise
transients (glitches). The BayesWave model has been extended to account
for gravitational wave signals with generic polarization content and the
simultaneous presence of signals and glitches in the data. We describe
updates in the BayesWave prior distributions, sampling proposals, and
burn-in stage that provide significantly improved sampling efficiency.
We present standard review checks indicating the robustness and
convergence of the BayesWave trans-dimensional sampler.
Journal reference: Phys. Rev. D 103, 044006 (2021)
----------------------------------------------------------------
arXiv:2101.01188 gr-qc astro-ph.HE
*Rapid and Robust Parameter Inference for Binary Mergers *
*Authors*: Neil J. Cornish
Abstract: The detection rate for compact binary mergers has grown as the
sensitivity of the global network of ground based gravitational wave
detectors has improved, now reaching the stage where robust automation
of the analyses is essential. Automated low-latency algorithms have been
developed that send out alerts when candidate signals are detected. The
alerts include sky maps to facilitate electromagnetic follow up
observations, along with probabilities that the system might contain a
neutron star, and hence be more likely to generate an electromagnetic
counterpart. Data quality issues, such as loud noise transients
(glitches), can adversely affect the low-latency algorithms, causing
false alarms and throwing off parameter estimation. Here a new analysis
method is presented that is robust against glitches, and capable of
producing fully Bayesian parameter inference, including sky maps and
mass estimates, in a matter of minutes. Key elements of the method are
wavelet-based de-noising, penalized maximization of the likelihood
during the initial search, rapid sky localization using pre-computed
inner products, and heterodyned likelihoods for full Bayesian inference.
Journal reference: Phys. Rev. D 103, 104057 (2021)
----------------------------------------------------------------
arXiv:2101.01200 gr-qc astro-ph.HE
*Modeling compact binary signals and instrumental glitches in
gravitational wave data *
*Authors*: Katerina Chatziioannou, Neil Cornish, Marcella Wijngaarden,
Tyson B. Littenberg
Abstract: Transient non-gaussian noise in gravitational wave detectors,
commonly referred to as glitches, pose challenges for inference of the
astrophysical properties of detected signals when the two are coincident
in time. Current analyses aim towards modeling and subtracting the
glitches from the data using a flexible, morphology-independent model in
terms of sine-gaussian wavelets before the signal source properties are
inferred using templates for the compact binary signal. We present a new
analysis of gravitational wave data that contain both a signal and
glitches by simultaneously modeling the compact binary signal in terms
of templates and the instrumental glitches using sine-gaussian wavelets.
The model for the glitches is generic and can thus be applied to a wide
range of glitch morphologies without any special tuning. The
simultaneous modeling of the astrophysical signal with templates allows
us to efficiently separate the signal from the glitches, as we
demonstrate using simulated signals injected around real O2 glitches in
the two LIGO detectors. We show that our new proposed analysis can
separate overlapping glitches and signals, estimate the compact binary
parameters, and provide ready-to-use glitch-subtracted data for
downstream inference analyses.
Journal reference: Phys. Rev. D 103, 044013 (2021)
----------------------------------------------------------------
arXiv:2103.14598 astro-ph.IM astro-ph.GA gr-qc
*Characterization of the stochastic signal originating from compact
binaries populations as measured by LISA *
*Authors*: Nikolaos Karnesis, Stanislav Babak, Mauro Pieroni, Neil
Cornish, Tyson Littenberg
Abstract: The Laser Interferometer Space Antenna (LISA) mission,
scheduled for launch in the early 2030s, is a gravitational wave
observatory in space designed to detect sources emitting in the
milli-Hertz band. In contrast to the present ground based detectors, the
LISA data are expected to be a signaldominated, with strong and weak
gravitational wave signals overlapping in time and in frequency.
Astrophysical population models predict a sufficient number of signals
in the LISA band to blend together and form an irresolvable foreground
noise. In this work, we present a generic method for characterizing the
foreground signals originating from a given astrophysical population of
coalescing compact binaries. Assuming idealized detector conditions and
perfect data analysis technique capable of identifying and removing the
bright sources, we apply an iterative procedure which allows us to
predict the different levels of foreground noise.
Journal reference: Phys. Rev. D 104, 043019 (2021)
----------------------------------------------------------------
arXiv:2104.04596 gr-qc
*New binary pulsar constraints on Einstein-æther theory after GW170817 *
*Authors*: Toral Gupta, Mario Herrero-Valea, Diego Blas, Enrico
Barausse, Neil Cornish, Kent Yagi, Nicolás Yunes
Abstract: The timing of millisecond pulsars has long been used as an
exquisitely precise tool for testing the building blocks of general
relativity, including the strong equivalence principle and Lorentz
symmetry. Observations of binary systems involving at least one
millisecond pulsar have been used to place bounds on the parameters of
Einstein-æther theory, a gravitational theory that violates Lorentz
symmetry at low energies via a preferred and dynamical time threading of
the spacetime manifold. However, these studies did not cover the region
of parameter space that is still viable after the recent bounds on the
speed of gravitational waves from GW170817/GRB170817A. The restricted
coverage was due to limitations in the methods used to compute the
pulsar sensitivities, which parameterize violations of the
strong-equivalence principle in these systems. We extend here the
calculation of pulsar sensitivities to the parameter space of
Einstein-æther theory that remains viable after GW170817/GRB170817A. We
show that observations of the damping of the period of quasi-circular
binary pulsars and of the triple system PSR J0337+1715 further constrain
the viable parameter space by about an order of magnitude over previous
constraints.
Journal reference: Class. Quantum Grav. 38 195003 (2021)
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arXiv:2105.02943 gr-qc astro-ph.HE
*Massive Black Hole Binaries and Where to Find Them with Dual Detector
Networks *
*Authors*: Kevin J. Shuman, Neil J. Cornish
Abstract: A single space-based gravitational wave detector will push the
boundaries of astronomy and fundamental physics. Having a network of two
or more detectors would significantly improve source localization. Here
we consider how dual networks of space-based detectors would improve
parameter estimation of massive black hole binaries. We consider two
scenarios: a network comprised of the Laser Interferometer Space Antenna
(LISA) and an additional LISA-like heliocentric detector (e.g. Taiji);
and a network comprised of LISA with an an additional geocentric
detector (e.g. TianQin). We use Markov chain Monte Carlo techniques and
Fisher matrix estimates to explore the impact of a two detector network
on sky localization and distance determination. The impact on other
source parameters is also studied. With the addition of a Taiji or
TianQin, we find orders of magnitude improvements in sky localization
for the more massive MBHBs, while also seeing improvements for lower
mass systems, and for other source parameters.
----------------------------------------------------------------
arXiv:2105.04283 gr-qc
*Spectral separation of the stochastic gravitational-wave background for
LISA in the context of a modulated Galactic foreground *
*Authors*: Guillaume Boileau, Astrid Lamberts, Nelson Christensen, Neil
J. Cornish, Renate Meyer
Abstract: Within its observational band the Laser Interferometer Space
Antenna, LISA, will simultaneously observe orbital modulated waveforms
from Galactic white dwarf binaries, a binary black hole produced
gravitational-wave background, and potentially a cosmologically created
stochastic gravitational-wave background (SGWB). The overwhelming
majority of stars end their lives as white dwarfs, making them very
numerous in the Milky Way. We simulate Galactic white dwarf binary
gravitational-wave emission based on distributions from various mock
catalogs and determine a complex waveform from the Galactic foreground
with 3.5×107 binaries. We describe the effects from the Galactic binary
distribution population across mass, position within the Galaxy, core
type, and orbital frequency distribution. We generate the modulated
Galactic white dwarf signal detected by \textit{LISA} due to its orbital
motion, and present a data analysis strategy to address it. The Fisher
Information and Markov Chain Monte Carlo methods give an estimation of
the \textit{LISA} noise and the parameters for the different signal
classes. We estimate the detectable limits for the future LISA
observation of the SGWB in the spectral domain with the 3 \textit{LISA}
channels A, E, and T. We simultaneously estimate the Galactic
foreground, the astrophysical and cosmological backgrounds. Assuming the
expected astrophysical background and a Galactic foreground, a
cosmological background energy density of around GW,Cosmo8×1013 could
be detected by LISA. LISA will either detect a cosmologically produced
SGWB, or set a limit that will have important consequences.
----------------------------------------------------------------
arXiv:2105.06793 gr-qc
*Spectral separation of the stochastic gravitational-wave background for
LISA: galactic, cosmological and astrophysical backgrounds *
*Authors*: Guillaume Boileau, Astrid Lamberts, Nelson Christensen, Neil
J. Cornish, Renate Meyer
Abstract: In its observation band, the Laser Interferometer Space
Antenna (LISA) will simultaneously observe stochastic gravitational-wave
background (SGWB) signals of different origins; orbitally modulated
waveforms from galactic white dwarf binaries, a binary black hole
produced background, and possibly a cosmologically produced SGWB. We
simulate the emission of gravitational waves from galactic white dwarf
binaries based on the Lamberts \cite{Lamberts} distributions and
determine a complex waveform from the galactic foreground. We generate
the modulated galactic signal detected by LISA due to its orbital
motion, and present a data analysis strategy to address it. The Fisher
Information and Markov Chain Monte Carlo methods give an estimate of the
LISA noise and parameters for the different signal sources. We
simultaneously estimate the galactic foreground, the astrophysical and
cosmological backgrounds, and estimate detection limits for the future
LISA observation of the SGWB in the spectral domain with the 3 LISA
channels A, E and T. In the context of the expected astrophysical
background and a galactic foreground, a cosmological background energy
density of about GW,Cosmo8×10^13 could be detected by LISA with our
spectral separation strategy.
----------------------------------------------------------------
arXiv:2107.02292 gr-qc astro-ph.CO
*A comparison of maximum likelihood mapping methods for
gravitational-wave backgrounds *
*Authors*: Arianna I. Renzini, Joseph D. Romano, Carlo R. Contaldi, Neil
J. Cornish
Abstract: Detection of a stochastic background of gravitational waves is
likely to occur in the next few years. Beyond searches for the isotropic
component of SGWBs, there have been various mapping methods proposed to
target anisotropic backgrounds. Some of these methods have been applied
to data taken by the Laser Interferometer Gravitational-wave
Observatories (LIGO) and Virgo. Specifically, these directional searches
have focused on mapping the intensity of the signal on the sky via
maximum likelihood solutions. We compare this intensity mapping approach
to a previously proposed, but never employed, amplitude-phase mapping
method to understand whether this latter approach may be employed in
future searches. We build up our understanding of the differences
between these two approaches by analysing simple toy models of
time-stream data, and run mock-data mapping tests for the two methods.
We find that the amplitude-phase method is only applicable to the case
of a background which is phase-coherent on large scales or, at the very
least, has an intrinsic coherence scale that is larger than that of the
detector. Otherwise, the amplitude-phase mapping method leads to a loss
of overall information, with respect to both phase and amplitude. Since
we do not expect these phase-coherent properties to hold for any of the
gravitational-wave background signals we hope to detect in the near
future, we conclude that intensity mapping is the preferred method for
such backgrounds.
----------------------------------------------------------------
arXiv:2109.02728 gr-qc
*Heterodyned Likelihood for Rapid Gravitational Wave Parameter Inference *
*Authors*: Neil J. Cornish
Abstract: Inferring the source properties of a gravitational wave signal
has traditionally been very computationally intensive and time
consuming. In recent years, several techniques have been developed that
can significantly reduce the computational cost while delivering rapid
and accurate parameter inference. One of the most powerful of these
techniques is the heterodyned likelihood, which uses a reference
waveform to base-band the likelihood calculation. Here an efficient
implementation of the heterodyned likelihood is presented that can be
used for a wide range of signal types and for both ground based and
space based interferometers. The computational savings relative to
direct calculation of the likelihood vary between two and four orders of
magnitude depending on the system. The savings are greatest for low mass
systems such as neutron star binaries. The heterodyning procedure can
incorporate marginalization over calibration uncertainties and the noise
power spectrum.
----------------------------------------------------------------
arXiv:2109.14706 gr-qc astro-ph.GA astro-ph.HE
*The NANOGrav 12.5-year data set: Search for Non-Einsteinian
Polarization Modes in theGravitational-Wave Background *
*Authors*: Zaven Arzoumanian, Paul T. Baker, Harsha Blumer, Bence Becsy,
Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Maria Charisi, Shami
Chatterjee, Siyuan Chen, James M. Cordes, Neil J. Cornish, Fronefield
Crawford, H. Thankful Cromartie, Megan E. DeCesar, Dallas M. DeGan, Paul
B. Demorest, Timothy Dolch, Brendan Drachler, Justin A. Ellis, Elizabeth
C. Ferrara, William Fiore, Emmanuel Fonseca, Nathan Garver-Daniels,
Peter A. Gentile , et al. (46 additional authors not shown)
Abstract: We search NANOGrav's 12.5-year data set for evidence of a
gravitational wave background (GWB) with all the spatial correlations
allowed by general metric theories of gravity. We find no substantial
evidence in favor of the existence of such correlations in our data. We
find that scalar-transverse (ST) correlations yield signal-to-noise
ratios and Bayes factors that are higher than quadrupolar (tensor
transverse, TT) correlations. Specifically, we find ST correlations with
a signal-to-noise ratio of 2.8 that are preferred over TT correlations
(Hellings and Downs correlations) with Bayesian odds of about 20:1.
However, the significance of ST correlations is reduced dramatically
when we include modeling of the Solar System ephemeris systematics
and/or remove pulsar J0030+0451 entirely from consideration. Even taking
the nominal signal-to-noise ratios at face value, analyses of simulated
data sets show that such values are not extremely unlikely to be
observed in cases where only the usual TT modes are present in the GWB.
In the absence of a detection of any polarization mode of gravity, we
place upper limits on their amplitudes for a spectral index of =5 and a
reference frequency of f_yr =1yr^1 . Among the upper limits for eight
general families of metric theories of gravity, we find the values of
A^95% _TT =(9.7±0.4)×10^16 and A^95% _ST =(1.4±0.03)×10^15 for the
family of metric spacetime theories that contain both TT and ST modes.
Journal reference: The Astrophysical Journal Letters, vol. 923, no. 2,
p. L22, Dec. 2021
----------------------------------------------------------------
arXiv:2110.06238 gr-qc astro-ph.HE
*Low Latency Detection of Massive Black Hole Binaries *
*Authors*: Neil J. Cornish
Abstract: The next decade is expected to see the launch of one or more
space based gravitational wave detectors: the European lead Laser
Interferometer Space Antenna (LISA); and one or more Chinese mission
concepts, Taiji and TianQin. One of the primary scientific targets for
these missions are the mergers of black holes with masses between 10^3
Mand 10^8 M. These systems may produce detectable electromagnetic
signatures in additional to gravitational waves due to the presence of
gas in mini-disks around each black hole, and a circumbinary disk
surrounding the system. The electromagnetic emission may occur before,
during and after the merger. In order to have the best chance of
capturing all phases of the emission it is imperative that the
gravitational wave signals can be detected in low latency, and used to
produce reliable estimates for the sky location and distance to help
guide the search for counterparts. The low latency detection also
provides a starting point for the ``global fit'' of the myriad signals
that are simultaneously present in the data. Here a low latency analysis
pipeline is presented that is capable of analyzing months of data in
just a few hours using a laptop from the last decade. The problem of
performing a global fit is avoided by whitening out the bright
foreground produced by nearby galactic binaries. The performance of the
pipeline is illustrated using simulated data from the LISA Data Challenge.
----------------------------------------------------------------
arXiv:2001.09793 gr-qc
*Prospects for Fundamental Physics with LISA *
Authors: Enrico Barausse, Emanuele Berti, Thomas Hertog, Scott A.
Hughes, Philippe Jetzer, Paolo Pani, Thomas P. Sotiriou, Nicola
Tamanini, Helvi Witek, Kent Yagi, Nicolas Yunes, T. Abdelsalhin, A.
Achucarro, K. V. Aelst, N. Afshordi, S. Akcay, L. Annulli, K. G. Arun,
I. Ayuso, V. Baibhav, T. Baker, H. Bantilan, T. Barreiro, C.
Barrera-Hinojosa, N. Bartolo , et al. (296 additional authors not shown)
Abstract: In this paper, which is of programmatic rather than
quantitative nature, we aim to further delineate and sharpen the future
potential of the LISA mission in the area of fundamental physics. Given
the very broad range of topics that might be relevant to LISA, we
present here a sample of what we view as particularly promising
directions, based in part on the current research interests of the LISA
scientific community in the area of fundamental physics. We organize
these directions through a "science-first" approach that allows us to
classify how LISA data can inform theoretical physics in a variety of
areas. For each of these theoretical physics classes, we identify the
sources that are currently expected to provide the principal
contribution to our knowledge, and the areas that need further
development. The classification presented here should not be thought of
as cast in stone, but rather as a fluid framework that is amenable to
change with the flow of new insights in theoretical physics.
Journal reference: Gen.Rel.Grav. 52 (2020) 8, 81
----------------------------------------------------------------
arXiv:2110.03428 gr-qc astro-ph.CO
*Dynamical Friction From Ultralight Dark Matter *
*Authors*: Yourong Wang, Richard Easther
Abstract: We simulate the gravitational dynamics of a massive object
interacting with Ultralight / Fuzzy Dark Matter (ULDM/FDM),
non-relativistic quantum matter described by the Schrodinger-Poisson
equation. We first consider a point mass moving in a uniform background,
and then a supermassive black hole (SMBH) moving within a ULDM soliton.
After replicating simple dynamical friction scenarios to verify our
numerical strategies, we demonstrate that the wake induced by a moving
mass in a uniform medium may undergo gravitational collapse that
dramatically increases the drag force, albeit in a scenario unlikely to
be encountered astrophysically. We broadly confirm simple estimates of
dynamical friction timescales for a black hole at the center of a halo
but see that a large moving point mass excites coherent "breathing
modes" in a ULDM soliton. These can lead to "stone skipping"
trajectories for point masses which do not sink uniformly toward the
center of the soliton, as well as stochastic motion near the center
itself. These effects will add complexity to SMBH-ULDM interactions and
to SMBH mergers in a ULDM universe.
----------------------------------------------------------------
arXiv:2002.06759 gr-qc
*Asymptotically flat vacuum initial data sets from a modified
parabolic-hyperbolic formulation of the Einstein vacuum constraint
equations *
*Authors*: Florian Beyer, Jörg Frauendiener, Joshua Ritchie
Abstract: In this paper we continue earlier investigations of
evolutionary formulations of the Einstein vacuum constraint equations
originally introduced by Rácz. Motivated by the strong evidence from
these works that the resulting vacuum initial data sets are generically
not asymptotically flat we analyse the asymptotics of the solutions of a
modified formulation by a combination of analytical and numerical
techniques. We conclude that the vacuum initial data sets generated with
this new formulation are generically asymptotically flat.
Journal reference: Phys. Rev. D 101, 084013 (2020)
----------------------------------------------------------------
arXiv:2005.11936 gr-qc math-ph
*Explorations of the infinite regions of space-time *
*Authors*: Florian Beyer, Jörg Frauendiener, Jörg Hennig
Abstract: An important concept in Physics is the notion of an isolated
system. It is used in many different areas to describe the properties of
a physical system which has been isolated from its environment. The
interaction with the `outside' is then usually reduced to a scattering
process, in which incoming radiation interacts with the system, which in
turn emits outgoing radiation. In Einstein's theory of gravitation
isolated systems are modeled as asymptotically flat space-times. They
provide the appropriate paradigm for the study of gravitational waves
and their interaction with a material system or even only with
themselves. In view of the emerging era of gravitational wave astronomy,
in which gravitational wave signals from many different astrophysical
sources are detected and interpreted, it is necessary to have a
foundation for the theoretical and numerical treatments of these
signals. Furthermore, from a purely mathematical point of view, it is
important to have a full understanding of the implications of imposing
the condition of asymptotic flatness onto solutions of the Einstein
equations. While it is known that there exists a large class of
asymptotically flat solutions of Einstein's equations, it is not known
what the necessary and sufficient conditions at infinity are that have
to be imposed on initial data so that they evolve into regular
asymptotically flat space-times. The crux lies in the region near
space-like infinity i0 where incoming and outgoing radiation `meet'. In
this paper we review the current knowledge and some of the analytical
and numerical work that has gone into the attempt to understand the
structure of asymptotically flat space-times near space-like and
null-infinity.
Journal reference: Int. J. Mod. Phys. D, 2030007, (2020)
----------------------------------------------------------------
arXiv:2104.13646 gr-qc math-ph
*A new look at the Bondi-Sachs energy-momentum *
*Authors*: Jörg Frauendiener, Chris Stevens
Abstract: How does one compute the Bondi mass on an arbitrary cut of
null infinity $\scri$ when it is not presented in a Bondi system? What
then is the correct definition of the mass aspect? How does one
normalise an asymptotic translation computed on a cut which is not
equipped with the unit-sphere metric? These are questions which need to
be answered if one wants to calculate the Bondi-Sachs energy-momentum
for a space-time which has been determined numerically. Under such
conditions there is not much control over the presentation of $\scri$ so
that most of the available formulations of the Bondi energy-momentum
simply do not apply. The purpose of this article is to provide the
necessary background for a manifestly conformally invariant and gauge
independent formulation of the Bondi energy-momentum. To this end we
introduce a conformally invariant version of the GHP formalism to
rephrase all the well-known formulae. This leads us to natural
definitions for the space of asymptotic translations with its Lorentzian
metric, for the Bondi news and the mass-aspect. A major role in these
developments is played by the "co-curvature", a naturally appearing
quantity closely related to the Gauß curvature on a cut of~$\scri$.
Journal reference: Class. Quantum Grav. 39 025007 (2022)
----------------------------------------------------------------
arXiv:2105.01906 gr-qc
*Can gravitational waves halt the expansion of the universe? *
*Authors*: Jörg Frauendiener, Jonathan Hakata, Chris Stevens
Abstract: We numerically investigate the propagation of plane
gravitational waves in the form of an initial boundary value problem
with de Sitter initial data. The full non-linear Einstein equations with
positive cosmological constant are written in the Friedrich-Nagy gauge
which yields a wellposed system. The propagation of a single wave and
the collision of two with colinear polarization are studied and
contrasted with their Minkowskian analogues. Unlike with =0, critical
behaviours are found with >0 and are based on the relationship between
the wave profile and . We find that choosing boundary data close to one
of these bifurcations results in a "false" steady state which violates
the constraints. Simulations containing (approximate) impulsive wave
profiles are run and general features are discussed. Analytic results of
Woodard and Tsamis, which describe how gravitational waves could affect
an expansion rate at an initial instance of time, are explored and
generalized to the entire space-time. Finally we put forward boundary
conditions that, at least locally, slow down the expansion considerably
for a time.
----------------------------------------------------------------
arXiv:2105.09515 gr-qc
*The non-linear perturbation of a black hole by gravitational waves. I.
The Bondi-Sachs mass loss *
*Authors*: Jörg Frauendiener, Chris Stevens
Abstract: The excitation of a black hole by infalling matter or
radiation has been studied for a long time, mostly in linear
perturbation theory. In this paper we study numerically the response of
a Schwarzschild black hole to an incoming gravitational wave pulse. We
present a numerically well-posed initial boundary value problem for the
generalized conformal field equations in which a wave profile for the
ingoing wave is specified at an outer time-like boundary which then hits
an initially static and spherically symmetric black hole. The non-linear
interaction of the black hole with the gravitational wave leads to
scattered radiation moving back out. The clean separation between
initial state and incoming radiation makes this setup ideal to study
scattering problems. The use of the conformal field equations allows us
to trace the response of the black hole to null infinity where we can
read off the scattered gravitational waves and compute the Bondi-Sachs
mass and the gravitational flux through I. In this way we check the
Bondi-Sachs mass loss formula directly on null infinity. We also comment
on comparisons with quasinormal modes.
----------------------------------------------------------------
arXiv:2001.08951 astro-ph.HE gr-qc
*A universal formula for the relativistic correction to the mutual
friction coupling time-scale in neutron stars *
*Authors*: Lorenzo Gavassino, Marco Antonelli, Pierre Pizzochero,
Brynmor Haskell
Abstract: Vortex-mediated mutual friction governs the coupling between
the superfluid and normal components in neutron star interiors. By, for
example, comparing precise timing observations of pulsar glitches with
theoretical predictions it is possible to constrain the physics in the
interior of the star, but to do so an accurate model of the mutual
friction coupling in general relativity is needed. We derive such a
model directly from Carter's multifluid formalism, and study the vortex
structure and coupling time-scale between the components in a
relativistic star. We calculate how general relativity modifies the
shape and the density of the quantized vortices and show that, in the
quasi-Schwarzschild coordinates, they can be approximated as straight
lines for realistic neutron star configurations. Finally, we present a
simple universal formula (given as a function of the stellar compactness
alone) for the relativistic correction to the glitch rise-time, which is
valid under the assumption that the superfluid reservoir is in a thin
shell in the crust or in the outer core. This universal relation can be
easily employed to correct, a posteriori, any Newtonian estimate for the
coupling time-scale, without any additional computational expense.
Journal reference: Monthly Notices of the Royal Astronomical Society,
Volume 494, Issue 3, May 2020, Pages 3562-3580
----------------------------------------------------------------
arXiv:2002.10357 astro-ph.HE astro-ph.SR gr-qc
*Magnetic field configurations in neutron stars from MHD simulations *
*Authors*: Ankan Sur, Brynmor Haskell, Emily Kuhn
Abstract: We have studied numerically the evolution of magnetic fields
in barotropic neutron stars, by performing nonlinear
magnetohydrodynamical simulations with the code PLUTO. For both
initially predominantly poloidal and toroidal fields, with varying
strengths, we find that the field settles down to a mixed
poloidal-toroidal configuration, where the toroidal component
contributes between 10% and 20% of the total magnetic energy. This is,
however, not a strict equilibrium, as the instability leads to the
development of turbulence, which in turn gives rise to an inverse
helicity cascade, which determines the final 'twisted torus' setup. The
final field configuration is thus dictated by the non-linear saturation
of the instability and is not stationary. The average energy of the
poloidal and toroidal components, however, is approximately stable in
our simulations, and a complex multipolar structure emerges at the
surface, while the magnetic field is dipolar at the exterior boundary,
outside the star.
Journal reference: Monthly Notices of the Royal Astronomical Society,
Volume 495, Issue 1, June 2020
----------------------------------------------------------------
arXiv:2003.04609 gr-qc astro-ph.HE
*Bulk viscosity in relativistic fluids: from thermodynamics to
hydrodynamics *
*Authors*: Lorenzo Gavassino, Marco Antonelli, Brynmor Haskell
Abstract: The approach of extended irreversible thermodynamics consists
of promoting the dissipative fluxes to non-equilibrium thermodynamic
variables. In a relativistic context, this naturally leads to the
formulation of the theory of Israel and Stewart (1979), which is, to
date, one of the most successful theories for relativistic dissipation.
Although the generality of the principle makes it applicable to any
dissipative fluid, a connection of the Israel-Stewart theory with
microphysics has been established, through kinetic theory, only for the
case of ideal quantum gases. By performing a convenient change of
variables, we provide, for the case of bulk viscosity, an equivalent
reformulation of the equations at the basis of extended irreversible
thermodynamics. This approach maps any thermodynamic process which
contributes to the bulk viscosity into a set of chemical reactions,
whose reaction coordinates are abstract parameters describing the
displacement from local thermodynamic equilibrium of the fluid element.
We apply our new formalism to the case of the relativistic fluids,
showing that the Israel-Stewart model for bulk viscosity is just the
second-order expansion of a minimal model belonging to a larger class of
non-perturbative theories for bulk viscosity which include the
nuclear-reaction-mediated bulk viscosity of neutron star matter as a
particular case. Furthermore, we show with concrete examples that our
formalism provides new ways of computing the bulk viscosity directly and
defines a simple prescription for constructing the Israel-Stewart model
for a generic bulk-viscous fluid.
Journal reference: Class. Quantum Grav. 38 075001 (2021)
----------------------------------------------------------------
arXiv:2006.09843 gr-qc astro-ph.HE hep-th
*When the entropy has no maximum: A new perspective on the instability
of the first-order theories of dissipation *
*Authors*: Lorenzo Gavassino, Marco Antonelli, Brynmor Haskell
Abstract: The first-order relativistic fluid theories of dissipation
proposed by Eckart and Landau-Lifshitz have been proved to be unstable.
They admit solutions which start in proximity of equilibrium and depart
exponentially from it. We show that this behaviour is due to the fact
that the total entropy of these fluids, restricted to the dynamically
accessible states, has no upper bound. As a result, these systems have
the tendency to constantly change according to the second law of
thermodynamics and the unstable modes represent the directions of growth
of the entropy in state space. We, then, verify that the conditions of
stability of Israel and Stewart's theory are exactly the requirements
for the entropy to have an absolute maximum. Hence, we explain how the
instability of the first-order theories is a direct consequence of the
truncation of the entropy current at the first order, which turns the
maximum into a saddle point of the total entropy. Finally, we show that
recently proposed first-order stable theories, constructed using more
general frames, do not solve the instability problem by providing a
maximum for the entropy, but, rather, are made stable by allowing for
small violations of the second law.
Journal reference: Phys. Rev. D 102, 043018 (2020)
----------------------------------------------------------------
arXiv:2007.09481 gr-qc astro-ph.HE
*Multifluid Modelling of Relativistic Radiation Hydrodynamics *
*Authors*: Lorenzo Gavassino, Marco Antonelli, Brynmor Haskell
Abstract: The formulation of a universal theory for bulk viscosity and
heat conduction represents a theoretical challenge for our understanding
of relativistic fluid dynamics. Recently, it has been shown that the
multifluid variational approach championed by Carter and collaborators
has the potential to be a general and natural framework to derive
(hyperbolic) hydrodynamic equations for relativistic dissipative
systems. Furthermore, it also allows to keep direct contact with
non-equilibrium thermodynamics, providing a clear microscopic
interpretation of the elements of the theory. To provide an example of
its universal applicability, in this paper we derive the fundamental
equations of the radiation hydrodynamics directly in the context of
Carter's multifluid theory. This operation unveils a novel set of
thermodynamic constraints that must be respected by any microscopic
model. Then, we prove that the radiation hydrodynamics becomes a
multifluid model for bulk viscosity or heat conduction in some
appropriate physical limits.
----------------------------------------------------------------
arXiv:2009.00030 astro-ph.HE astro-ph.SR gr-qc
*Return of the Big Glitcher: NICER timing and glitches of PSR J0537-6910 *
*Authors*: Wynn C. G. Ho, Cristobal M. Espinoza, Zaven Arzoumanian,
Teruaki Enoto, Tsubasa Tamba, Danai Antonopoulou, Michal Bejger,
Sebastien Guillot, Brynmor Haskell, Paul S. Ray
Abstract: PSR J0537-6910, also known as the Big Glitcher, is the most
prolific glitching pulsar known, and its spin-induced pulsations are
only detectable in X-ray. We present results from analysis of 2.7 years
of NICER timing observations, from 2017 August to 2020 April. We obtain
a rotation phase-connected timing model for the entire timespan, which
overlaps with the third observing run of LIGO/Virgo, thus enabling the
most sensitive gravitational wave searches of this potentially strong
gravitational wave-emitting pulsar. We find that the short-term braking
index between glitches decreases towards a value of 7 or lower at longer
times since the preceding glitch. By combining NICER and RXTE data, we
measure a long-term braking index n=-1.25+/-0.01. Our analysis reveals 8
new glitches, the first detected since 2011, near the end of RXTE, with
a total NICER and RXTE glitch activity of 8.88x10^-7 yr^-1. The new
glitches follow the seemingly unique time-to-next-glitch---glitch-size
correlation established previously using RXTE data, with a slope of 5 d
microHz^-1. For one glitch around which NICER observes two days on
either side, we search for but do not see clear evidence of spectral nor
pulse profile changes that may be associated with the glitch.
Journal reference: Mon. Not. R. Astron. Soc. 498, 4605-4614 (2020)
----------------------------------------------------------------
arXiv:2010.15574 astro-ph.HE astro-ph.SR gr-qc
doi
10.1093/mnras/stab307
Gravitational waves from mountains in newly born millisecond magnetars
Authors: Ankan Sur, Brynmor Haskell
Abstract: In this paper we study the spin-evolution and
gravitational-wave luminosity of a newly born millisecond magnetar,
formed either after the collapse of a massive star or after the merger
of two neutron stars. In both cases we consider the effect of fallback
accretion, and consider the evolution of the system due to the different
torques acting on the star, namely the spin up torque due to accretion
and spin-down torques due to magnetic dipole radiation, neutrino
emission, and gravitational wave emission linked to the formation of a
`mountain' on the accretion poles. Initially the spin period is mostly
affected by the dipole radiation, but at later times accretion spin the
star up rapidly. We find that a magnetar formed after the collapse of a
massive star can accrete up to 1 M_{\odot} , and survive on the order of
50 s before collapsing to a black hole. The gravitational wave strain,
for an object located at 1 Mpc, is h_c \sim 10^{-23} at kHz frequencies,
making this a potential target for next generation ground based
detectors. A magnetar formed after a binary neutron star merger, on the
other hand, accretes at the most 0.2 M_{\odot}, and emits gravitational
waves with a lower maximum strain of the order of h_c \sim 10^{-24} ,
but also survives for much longer times, and may possibly be associated
with the X-ray plateau observed in the light curve of a number of short
gamma-ray burst.
Journal reference: Monthly Notices of the Royal Astronomical Society,
Volume 502, Issue 4, April 2021, Pages 4680-4688
----------------------------------------------------------------
arXiv:2011.10557 astro-ph.HE gr-qc
*Axisymmetric models for neutron star merger remnants with realistic
thermal and rotational profiles *
*Authors*: Giovanni Camelio, Tim Dietrich, Stephan Rosswog, Brynmor Haskell
Abstract: Merging neutron stars are expected to produce hot, metastable
remnants in rapid differential rotation, which subsequently cool and
evolve into rigidly rotating neutron stars or collapse to black holes.
Studying this metastable phase and its further evolution is essential
for the prediction and interpretation of the electromagnetic, neutrino,
and gravitational signals from such a merger. In this work, we model
binary neutron star merger remnants and propose new rotation and thermal
laws that describe post-merger remnants. Our framework is capable to
reproduce quasi-equilibrium configurations for generic equations of
state, rotation and temperature profiles, including nonbarotropic ones.
We demonstrate that our results are in agreement with numerical
relativity simulations concerning bulk remnant properties like the mass,
angular momentum, and the formation of a massive accretion disk. Because
of the low computational cost for our axisymmetric code compared to full
3+1-dimensional simulations, we can perform an extensive exploration of
the binary neutron star remnant parameter space studying several hundred
thousand configurations for different equation of states.
Journal reference: Phys. Rev. D 103, 063014 (2021)
----------------------------------------------------------------
arXiv:2012.10288 astro-ph.HE cond-mat.quant-gas gr-qc physics.flu-dyn
*Superfluid dynamics in neutron star crusts: the Iordanskii force and
chemical gauge covariance *
*Authors*: Lorenzo Gavassino, Marco Antonelli, Brynmor Haskell
Abstract: We present a geometrical derivation of the relativistic
dynamics of the superfluid inner crust of a neutron star. The resulting
model is analogous to the Hall-Vinen-Bekarevich-Khalatnikov
hydrodynamics for a single-component superfluid at finite temperature,
but particular attention should be paid to the fact that some fraction
of the neutrons are locked to the motion of the protons in nuclei. This
gives rise to an ambiguity in the definition of the two currents (the
normal and the superfluid one) on which the model is built, a problem
that manifests itself as a chemical gauge freedom of the theory. To
ensure chemical gauge covariance of the hydrodynamic model, the
phenomenological equation of motion for a quantized vortex should
contain an extra transverse force, that is the relativistic version of
the Iordanskii force discussed in the context of superfluid Helium.
Hence, we extend the mutual friction model of Langlois et al. (1998) to
account for the possible presence of this Iordanskii-like force.
Furthermore, we propose that a better understanding of the (still not
completely settled) controversy around the presence of the Iordanskii
force in superfluid Helium, as well as in neutron stars, may be achieved
by considering that the different incompatible results present in the
literature pertain to two, opposite, dynamical regimes of the fluid system.
Journal reference: Universe 2021, 7(2), 28
----------------------------------------------------------------
arXiv:2104.03137 gr-qc
*Gravitational waves from isolated neutron stars *
*Authors*: Brynmor Haskell, Kai Schwenzer
Abstract: Neutron star interiors are a fantastic laboratory for high
density physics in extreme environments. Probing this system with
standard electromagnetic observations is, however, a challenging
endeavour, as the radiation tends to be scattered by the outer layers
and the interstellar medium. Gravitational waves, on the other hand,
while challenging to detect, interact weakly with matter and are likely
to carry a clean imprint of the high density interior of the star. In
particular long lived, i.e. `continuous' signals from isolated neutron
stars can carry a signature of deformations, possibly in crystalline
exotic layers of the core, or allow to study modes of oscillation, thus
performing gravitational wave asteroseismology of neutron star
interiors. In this article we will review current theoretical models for
continuous gravitational wave emission, and observational constraints,
both electromagnetic and gravitational. Finally we will discuss future
observational possibilities.
----------------------------------------------------------------
arXiv:2105.14621 gr-qc astro-ph.HE hep-ph physics.flu-dyn
*Thermodynamic stability implies causality *
*Authors*: Lorenzo Gavassino, Marco Antonelli, Brynmor Haskell
Abstract: The stability conditions of a relativistic hydrodynamic theory
can be derived directly from the requirement that the entropy should be
maximised in equilibrium. Here we use a simple geometrical argument to
prove that, if the hydrodynamic theory is stable according to this
entropic criterion, then localised perturbations to the equilibrium
state cannot propagate outside their future light-cone. In other words,
within relativistic hydrodynamics, acausal theories must be
thermodynamically unstable, at least close to equilibrium. We show that
the physical origin of this deep connection between stability and
causality lies in the relationship between entropy and information. Our
result may be interpreted as an ``equilibrium conservation theorem'',
which generalizes the Hawking-Ellis vacuum conservation theorem to
finite temperature and chemical potential.
----------------------------------------------------------------
arXiv:2108.11858 astro-ph.HE astro-ph.SR gr-qc
*Long-term GRHMD simulation of magnetic field in isolated neutron stars *
*Authors*: Ankan Sur, William Cook, David Radice, Brynmor Haskell,
Sebastiano Bernuzzi
Abstract: Strong magnetic fields play an important role in powering the
emission of neutron stars. Nevertheless a full understanding of the
interior configuration of the field remains elusive. In this work, we
present General Relativistic MagnetoHydroDynamics simulations of the
magnetic field evolution in neutron stars lasting 500 ms (5 Alfven
crossing times) and up to resolutions of 0.231 km using Athena++. We
explore two different initial conditions, one with purely poloidal
magnetic field and the other with a dominant toroidal component, and
study the poloidal and toroidal field energies, the growth times of the
various instability-driven oscillation modes and turbulence. We find
that the purely poloidal setup generates a toroidal field which later
decays exponentially reaching 1% of the total magnetic energy, showing
no evidence of reaching equilibrium. The initially stronger toroidal
field setup, on the other hand, loses up to 20% of toroidal energy and
maintains this state till the end of our simulation. We also explore the
hypothesis, drawn from previous MHD simulations, that turbulence plays
an important role in the quasi equilibrium state. An analysis of the
spectra in our higher resolution setups reveal, however, that in most
cases we are not observing turbulence at small scales, but rather a
noisy velocity field inside the star. We also observe that the majority
of the magnetic energy gets dissipated as heat increasing the internal
energy of the star, while a small fraction gets radiated away as
electromagnetic radiation.
----------------------------------------------------------------
arXiv:2110.05546 gr-qc astro-ph.HE nucl-th physics.flu-dyn
*Extending Israel and Stewart hydrodynamics to relativistic superfluids
via Carter's multifluid approach *
*Authors*: Lorenzo Gavassino, Marco Antonelli, Brynmor Haskell
Abstract: We construct a relativistic model for bulk viscosity and heat
conduction in a superfluid. Building on the principles of Unified
Extended Irreversible Thermodynamics, the model is derived from Carter's
multifluid approach for a theory with three currents, where the
quasi-particle current is an independent hydrodynamic degree of freedom.
For small deviations from local thermodynamic equilibrium, the model
reduces to an extension of the Israel-Stewart theory to superfluid
systems. It can, therefore, be made hyperbolic, causal and stable if the
microscopic input is accurate. The non-dissipative limit of the model is
the relativistic two-fluid model of Carter, Khalatnikov and Gusakov. The
Newtonian limit of the model is an Extended-Irreversible-Thermodynamic
extension of Landau's two-fluid model. The model predicts the existence
of four bulk viscosity coefficients and accounts for their microscopic
origin, providing their exact formulas in terms of the quasi-particle
creation rate. Furthermore, when fast oscillations of small amplitude
around the equilibrium are considered, the relaxation-time term in the
telegraph-type equations for the bulk viscosities accounts directly for
their expected dependence on the frequency.
----------------------------------------------------------------
arXiv:2009.03992 gr-qc math-ph
*Axis potentials for stationary n-black-hole configurations *
*Authors*: Jörg Hennig
Abstract: We extend earlier discussions of the balance problem for two
black holes and study stationary spacetimes containing an arbitrary
number of n aligned rotating and (possibly) charged black holes. For
these hypothetical equilibrium configurations, we obtain the most
general form of the boundary data on the symmetry axis in terms of a
finite number of parameters. Hence future investigations of n-black-hole
configurations can be restricted to studying properties of these finite
families of solutions.
Journal reference: Class. Quantum Grav. 37, 19LT01 (2020)
----------------------------------------------------------------
arXiv:2012.02240 gr-qc math-ph
*Fully pseudospectral solution of the conformally invariant wave
equation on a Kerr background *
*Authors*: Jörg Hennig, Rodrigo Panosso Macedo
Abstract: We study axisymmetric solution to the conformally invariant
wave equation on a Kerr background by means of numerical and analytical
methods. Our main focus is on the behaviour of the solutions near
spacelike infinity, which is appropriately represented as a cylinder.
Earlier studies of the wave equation on a Schwarzschild background have
revealed important details about the regularity of the corresponding
solutions. It was found that, on the cylinder, the solutions generically
develop logarithmic singularities at infinitely many orders. Moreover,
these singularities also `spread' to future null infinity. However, by
imposing certain regularity conditions on the initial data, the
lowest-order singularities can be removed. Here we are interested in a
generalisation of these results to a rotating black hole background and
study the influence of the rotation rate on the properties of the
solutions. To this aim, we first construct a conformal compactification
of the Kerr solution which yields a suitable representation of the
cylinder at spatial infinity. Besides analytical investigations on the
cylinder, we numerically solve the wave equation with a fully
pseudospectral method, which allows us to obtain highly accurate
numerical solutions. This is crucial for a detailed analysis of the
regularity of the solutions. In the Schwarzschild case, the numerical
problem could effectively be reduced to solving (1+1)-dimensional
equations. Here we present a code that can perform the full 2+1
evolution as required for axisymmetric waves on a Kerr background.
Journal reference: Class. Quantum Grav. 38, 135006 (2021)
----------------------------------------------------------------
arXiv:2001.06102 astro-ph.HE gr-qc nucl-th
*Gravitational waves or deconfined quarks: what causes the premature
collapse of neutron stars born in short gamma-ray bursts? *
*Authors*: Nikhil Sarin, Paul D. Lasky, Gregory Ashton
Abstract: We infer the collapse times of long-lived neutron stars into
black holes using the X-ray afterglows of 18 short gamma-ray bursts. We
then apply hierarchical inference to infer properties of the neutron
star equation of state and dominant spin-down mechanism. We measure the
maximum non-rotating neutron star mass M_TOV =2.31^+0.36 _0.21 Mand
constrain the fraction of remnants spinning down predominantly through
gravitational-wave emission to =0.69^+0.21 _0.39 with 68%
uncertainties. In principle, this method can determine the difference
between hadronic and quark equation of states. In practice, however, the
data is not yet informative with indications that these neutron stars do
not have hadronic equation of states at the 1 level. These inferences
all depend on the underlying progenitor mass distribution for short
gamma-ray bursts produced by binary neutron star mergers. The recently
announced gravitational-wave detection of GW190425 suggests this
underlying distribution is different from the locally-measured
population of double neutron stars. We show that M_TOV and constraints
depend on the fraction of binary mergers that form through a
distribution consistent with the locally-measured population and a
distribution that can explain GW190425. The more binaries that form from
the latter distribution, the larger M_TOV needs to be to satisfy the
X-ray observations. Our measurements above are marginalised over this
unknown fraction. If instead, we assume GW190425 is not a binary neutron
star merger, i.e the underlying mass distribution of double neutron
stars is the same as observed locally, we measure M_TOV =2.26^+0.31
_0.17 M.
Journal reference: Phys. Rev. D 101, 063021 (2020)
----------------------------------------------------------------
arXiv:2003.09780 astro-ph.IM astro-ph.HE gr-qc
*The Parkes Pulsar Timing Array Project: Second data release *
*Authors*: M. Kerr, D. J. Reardon, G. Hobbs, R. M. Shannon, R. N.
Manchester, S. Dai, C. J. Russell, S. -B. Zhang, W. van Straten, S.
Osowski, A. Parthasarathy, R. Spiewak, M. Bailes, N. D. R. Bhat, A. D.
Cameron, W. A. Coles, J. Dempsey, X. Deng, B. Goncharov, J. F Kaczmarek,
M. J. Keith, P. D. Lasky, M. E. Lower, B. Preisig, J. M. Sarkissian , et
al. (5 additional authors not shown)
Abstract: We describe 14 years of public data from the Parkes Pulsar
Timing Array (PPTA), an ongoing project that is producing precise
measurements of pulse times of arrival from 26 millisecond pulsars using
the 64-m Parkes radio telescope with a cadence of approximately three
weeks in three observing bands. A comprehensive description of the
pulsar observing systems employed at the telescope since 2004 is
provided, including the calibration methodology and an analysis of the
stability of system components. We attempt to provide full accounting of
the reduction from the raw measured Stokes parameters to pulse times of
arrival to aid third parties in reproducing our results. This conversion
is encapsulated in a processing pipeline designed to track provenance.
Our data products include pulse times of arrival for each of the pulsars
along with an initial set of pulsar parameters and noise models. The
calibrated pulse profiles and timing template profiles are also
available. These data represent almost 21,000 hrs of recorded data
spanning over 14 years. After accounting for processes that induce
time-correlated noise, 22 of the pulsars have weighted root-mean-square
timing residuals of < 1 s in at least one radio band. The data should
allow end users to quickly undertake their own gravitational-wave
analyses (for example) without having to understand the intricacies of
pulsar polarisation calibration or attain a mastery of radio-frequency
interference mitigation as is required when analysing raw data files.
----------------------------------------------------------------
arXiv:2006.04396 astro-ph.HE gr-qc
*Detection and parameter estimation of binary neutron star merger remnants *
*Authors*: Paul J. Easter, Sudarshan Ghonge, Paul D. Lasky, Andrew R.
Casey, James A. Clark, Francisco Hernandez Vivanco, Katerina Chatziioannou
Abstract: Detection and parameter estimation of binary neutron star
merger remnants can shed light on the physics of hot matter at
supranuclear densities. Here we develop a fast, simple model that can
generate gravitational waveforms, and show it can be used for both
detection and parameter estimation of post-merger remnants. The model
consists of three exponentially-damped sinusoids with a linear
frequency-drift term. The median fitting factors between the model
waveforms and numerical-relativity simulations exceed 0.90. We detect
remnants at a post-merger signal-to-noise ratio of 7 using a
Bayes-factor detection statistic with a threshold of 3000. We can
constrain the primary post-merger frequency to ±^1.4 _1.2 % at
post-merger signal-to-noise ratios of 15 with an increase in precision
to ±^0.3 _0.2 % for post-merger signal-to-noise ratios of 50. The tidal
coupling constant can be constrained to ±^9 _12 % at post-merger
signal-to-noise ratios of 15, and ±5% at post-merger signal-to-noise
ratios of 50 using a hierarchical inference model.
Journal reference: Phys. Rev. D 102, 043011 (2020).
----------------------------------------------------------------
arXiv:2006.11525 gr-qc astro-ph.CO
*Mapping the Universe Expansion: Enabling percent-level measurements of
the Hubble Constant with a single binary neutron-star merger detection *
*Authors*: Juan Calderón Bustillo, Samson H. W. Leong, Tim Dietrich,
Paul D. Lasky
Abstract: The joint observation of the gravitational-wave and
electromagnetic signal from the binary neutron-star merger GW170817
allowed for a new independent measurement of the Hubble constant H_0 ,
albeit with an uncertainty of about 15% at 1. Observations of similar
sources with a network of future detectors will allow for more precise
measurements of H_0 . These, however, are currently largely limited by
the intrinsic degeneracy between the luminosity distance and the
inclination of the source in the gravitational-wave signal. We show that
the higher-order modes in gravitational waves can be used to break this
degeneracy in astrophysical parameter estimation in both the inspiral
and post-merger phases of a neutron star merger. We show that for
systems at distances similar to GW170817, this method enables
percent-level measurements of H_0 with a single detection. This would
permit the study of time variations and spatial anisotropies of H_0 with
unprecedented precision. We investigate how different network
configurations affect measurements of H_0 , and discuss the implications
in terms of science drivers for the proposed 2.5- and third-generation
gravitational-wave detectors. Finally, we show that the precision of H_0
measured with these future observatories will be solely limited by
redshift measurements of electromagnetic counterparts.
Journal reference: The Astrophysical Journal Letters, Volume 912, Number
1 (2021)
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arXiv:2006.11957 stro-ph.CO gr-qc
*Searching for anisotropy in the distribution of binary black hole mergers *
*Authors*: Ethan Payne, Sharan Banagiri, Paul Lasky, Eric Thrane
Abstract: The standard model of cosmology is underpinned by the
assumption of the statistical isotropy of the Universe. Observations of
the cosmic microwave background, galaxy distributions, and supernovae,
among other media, support the assumption of isotropy at scales 100
Mpc. The recent detections of gravitational waves from merging
stellar-mass binary black holes provide a new probe of anisotropy;
complementary and independent of all other probes of the matter
distribution in the Universe. We present an analysis using a spherical
harmonic model to determine the level of anisotropy in the first
LIGO/Virgo transient catalog. We find that the ten binary black hole
mergers within the first transient catalog are consistent with an
isotropic distribution. We carry out a study of simulated events to
assess the prospects for future probes of anisotropy. Within a single
year of operation, third-generation gravitational-wave observatories
will probe anisotropies with an angular scale of 36at the level of 0.1%.
Journal reference: Phys. Rev. D 102, 102004 (2020)
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arXiv:2009.10193 astro-ph.IM astro-ph.HE gr-qc
*Gravitational-wave astronomy with a physical calibration model *
*Authors*: Ethan Payne, Colm Talbot, Paul D. Lasky, Eric Thrane, Jeffrey
S. Kissel
Abstract: We carry out astrophysical inference for compact binary merger
events in LIGO-Virgo's first gravitational-wave transient catalog
(GWTC-1) using a physically motivated calibration model. We demonstrate
that importance sampling can be used to reduce the cost of what would
otherwise be a computationally challenging analysis. We show that
including the physical estimate for the calibration error distribution
has negligible impact on the inference of parameters for the events in
GWTC-1. Studying a simulated signal with matched filter signal-to-noise
ratio SNR=200, we project that a calibration error estimate typical of
GWTC-1 is likely to be negligible for the current generation of
gravitational-wave detectors. We argue that other sources of systematic
error---from waveforms, prior distributions, and noise modelling---are
likely to be more important. Finally, using the events in GWTC-1 as
standard sirens, we infer an astrophysically-informed improvement on the
estimate of the calibration error in the LIGO interferometers.
Journal reference: Phys. Rev. D 102, 122004 (2020)
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arXiv:2010.01857 gr-qc
*Black-hole spectroscopy, the no-hair theorem and GW150914: Kerr vs. Occam *
*Authors*: Juan Calderón Bustillo, Paul D. Lasky, Eric Thrane
Abstract: The "no-hair" theorem states that astrophysical black holes
are fully characterised by just two numbers: their mass and spin. The
gravitational-wave emission from a perturbed black-hole consists of a
superposition of damped sinusoids, known as \textit{quasi-normal modes}.
Quasi-normal modes are specified by three integers (,m,n): the (,m)
integers describe the angular properties and (n) specifies the
(over)tone. If the no-hair theorem holds, the frequencies and damping
times of quasi-normal modes are determined uniquely by the mass and spin
of the black hole, while phases and amplitudes depend on the particular
perturbation. Current tests of the no-hair theorem, attempt to identify
these modes in a semi-agnostic way, without imposing priors on the
source of the perturbation. This is usually known as \textit{black-hole
spectroscopy}. Applying this framework to GW150914, the measurement of
the first overtone led to the confirmation of the theorem to 20% level.
We show, however, that such semi-agnostic tests cannot provide strong
evidence in favour of the no-hair theorem, even for extremely loud
signals, given the increasing number of overtones (and free parameters)
needed to fit the data. This can be solved by imposing prior assumptions
on the origin of the perturbed black hole that can further constrain the
explored parameters: in particular, our knowledge that the ringdown is
sourced by a binary black hole merger. Applying this strategy to
GW150914 we find a natural log Bayes factor of 6.5 in favour of the
Kerr nature of its remnant, indicating that the hairy object hypothesis
is disfavoured with <1:600 with respect to the Kerr black-hole one.
Journal reference: Phys. Rev. D 103, 024041 (2021)
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arXiv:2012.08172 astro-ph.HE gr-qc
*The evolution of binary neutron star post-merger remnants: a review *
*Authors*: Nikhil Sarin, Paul D. Lasky
Abstract: Two neutron stars merge somewhere in the Universe
approximately every 10 seconds, creating violent explosions observable
in gravitational waves and across the electromagnetic spectrum. The
transformative coincident gravitational-wave and electromagnetic
observations of the binary neutron star merger GW170817 gave invaluable
insights into these cataclysmic collisions, probing bulk nuclear matter
at supranuclear densities, the jet structure of gamma-ray bursts, the
speed of gravity, and the cosmological evolution of the local Universe,
among other things. Despite the wealth of information, it is still
unclear when the remnant of GW170817 collapsed to form a black hole.
Evidence from other short gamma-ray bursts indicates a large fraction of
mergers may form long-lived neutron stars. We review what is known
observationally and theoretically about binary neutron star post-merger
remnants. From a theoretical perspective, we review our understanding of
the evolution of short- and long-lived merger remnants, including fluid,
magnetic-field, and temperature evolution. These considerations impact
prospects of detection of gravitational waves from either short- or
long-lived neutron star remnants which potentially allows for new probes
into the hot nuclear equation of state in conditions inaccessible in
terrestrial experiments. We also review prospects for determining
post-merger physics from current and future electromagnetic
observations, including kilonovae and late-time x-ray and radio
afterglow observations.
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arXiv:2103.12274 gr-qc astro-ph.HE astro-ph.IM
*Bayesian inference for gravitational waves from binary neutron star
mergers in third-generation observatories *
*Authors*: Rory Smith, Ssohrab Borhanian, Bangalore Sathyaprakash,
Francisco Hernandez Vivanco, Scott Field, Paul Lasky, Ilya Mandel,
Soichiro Morisaki, David Ottaway, Bram Slagmolen, Eric Thrane, Daniel
Töyrä, Salvatore Vitale
Abstract: Third-generation (3G) gravitational-wave detectors will
observe thousands of coalescing neutron star binaries with unprecedented
fidelity. Extracting the highest precision science from these signals is
expected to be challenging owing to both high signal-to-noise ratios and
long-duration signals. We demonstrate that current Bayesian inference
paradigms can be extended to the analysis of binary neutron star signals
without breaking the computational bank. We construct reduced order
models for 90minute long gravitational-wave signals, covering the
observing band (52048Hz), speeding up inference by a factor of 1.3×104
compared to the calculation times without reduced order models. The
reduced order models incorporate key physics including the effects of
tidal deformability, amplitude modulation due to the Earth's rotation,
and spin-induced orbital precession. We show how reduced order modeling
can accelerate inference on data containing multiple, overlapping
gravitational-wave signals, and determine the speedup as a function of
the number of overlapping signals. Thus, we conclude that Bayesian
inference is computationally tractable for the long-lived, overlapping,
high signal-to-noise-ratio events present in 3G observatories.
Journal reference: Phys. Rev. Lett. 127, 081102 (2021)
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arXiv:2105.02879 gr-qc astro-ph.HE
*The Memory Remains (Undetected): Updates from the Second LIGO/Virgo
Gravitational-Wave Transient Catalog *
*Authors*: Moritz Hübner, Paul Lasky, Eric Thrane
Abstract: The LIGO and Virgo observatories have reported 39 new
gravitational-wave detections during the first part of the third
observation run, bringing the total to 50. Most of these new detections
are consistent with binary black-hole coalescences, making them suitable
targets to search for gravitational-wave memory, a non-linear effect of
general relativity. We extend a method developed in previous
publications to analyse these events to determine a Bayes factor
comparing the memory hypothesis to the no-memory hypothesis.
Specifically, we calculate Bayes factors using two waveform models with
higher-order modes that allow us to analyse events with extreme mass
ratios and precessing spins, both of which have not been possible
before. Depending on the waveform model we find a combined lnBF_mem
=0.024 or lnBF_mem =0.049 in favour of memory. This result is consistent
with recent predictions that indicate O(2000) binary black-hole
detections will be required to confidently establish the presence or
absence of memory.
Journal reference: Phys. Rev. D 104, 023004 (2021)
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arXiv:2106.04064 astro-ph.HE gr-qc
*Can we measure the collapse time of a post-merger remnant for a future
GW170817-like event? *
*Authors*: Paul J. Easter, Paul D. Lasky, Andrew R. Casey
Abstract: Measuring the collapse time of a binary neutron star merger
remnant can inform the physics of extreme matter and improve modelling
of short gamma-ray bursts and associated kilonova. The lifetime of the
post-merger remnant directly impacts the mechanisms available for the
jet launch of short gamma-ray bursts. We develop and test a method to
measure the collapse time of post-merger remnants. We show that for a
GW170817-like event at 40Mpc, a network of Einstein Telescope with
Cosmic Explorer is required to detect collapse times of 10ms. For a
two-detector network at A+ design sensitivity, post-merger remnants with
collapse times of 10ms must be 10Mpc to be measureable. This increases
to 1826Mpc if we include the proposed Neutron star Extreme Matter
Observatory (NEMO), increasing the effective volume by a factor of 30.
----------------------------------------------------------------
arXiv:2106.09042 astro-ph.HE gr-qc
*Implications of Eccentric Observations on Binary Black Hole Formation
Channels *
*Authors*: Michael Zevin, Isobel M. Romero-Shaw, Kyle Kremer, Eric
Thrane, Paul D. Lasky
Abstract: Orbital eccentricity is one of the most robust discriminators
for distinguishing between dynamical and isolated formation scenarios of
binary black hole mergers using gravitational-wave observatories such as
LIGO and Virgo. Using state-of-the-art cluster models, we show how
selection effects impact the detectable distribution of eccentric
mergers from clusters. We show that the observation (or lack thereof) of
eccentric binary black hole mergers can significantly constrain the
fraction of detectable systems that originate from dynamical
environments, such as dense star clusters. After roughly 150
observations, observing no eccentric binary signals would indicate that
clusters cannot make up the majority of the merging binary black hole
population in the local universe (95% credibility). However, if dense
star clusters dominate the rate of eccentric mergers and a single system
is confirmed to be measurably eccentric in the first and second
gravitational-wave transient catalogs, clusters must account for at
least 14% of detectable binary black hole mergers. The constraints on
the fraction of detectable systems from dense star clusters become
significantly tighter as the number of eccentric observations grows and
will be constrained to within 0.5 dex once 10 eccentric binary black
holes are observed.
Journal reference: The Astrophysical Journal Letters, 921, L43 (2021)
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arXiv:2107.11730 gr-qc astro-ph.HE
*The imprint of superradiance on hierarchical black hole mergers *
*Authors*: Ethan Payne, Ling Sun, Kyle Kremer, Paul D. Lasky, Eric Thrane
Abstract: Ultralight bosons are a proposed solution to outstanding
problems in cosmology and particle physics: they provide a dark-matter
candidate while potentially explaining the strong charge-parity problem.
If they exist, ultralight bosons can interact with black holes through
the superradiant instability. In this work we explore the consequences
of this instability on the evolution of hierarchical black holes within
dense stellar clusters. By reducing the spin of individual black holes,
superradiance reduce the recoil velocity of merging binary black holes,
which, in turn, increases the retention fraction of hierarchical merger
remnants. We show that the existence of ultralight bosons with mass
2×10^14 /eV2×10^13 would lead to an increased rate of hierarchical
black hole mergers in nuclear star clusters. An ultralight boson in this
energy range would result in up to 60% more present-day nuclear star
clusters supporting hierarchical growth. The presence of an ultralight
boson can also double the rate of intermediate mass black hole mergers
to 0.08 Gpc^3 yr^1 in the local Universe. These results imply that a
select range of ultralight boson mass can have far-reaching consequences
for the population of black holes in dense stellar environments. Future
studies into black hole cluster populations and the spin distribution of
hierarchically formed black holes will test this scenario.
----------------------------------------------------------------
arXiv:2110.10892 astro-ph.HE gr-qc
*Multimessenger astronomy with a kHz-band gravitational-wave observatory *
*Authors*: Nikhil Sarin, Paul D. Lasky
Abstract: Proposed next-generation networks of gravitational-wave
observatories include dedicated kilohertz instruments that target
neutron star science, such as the proposed Neutron Star Extreme Matter
Observatory, NEMO. The original proposal for NEMO highlighted the need
for it to exist in a network of gravitational-wave observatories to
ensure detection confidence and sky localisation of sources. We show
that NEMO-like observatories have significant utility on their own as
coincident electromagnetic observations can provide the detection
significance and sky localisation. We show that, with a single NEMO-like
detector and expected electromagnetic observatories in the late 2020s
and early 2030s such as the Vera C. Rubin observatory and SVOM,
approximately 40% of all binary neutron star mergers detected with
gravitational waves could be confidently identified as coincident
multimessenger detections. We show that we expect 2^+10 _1 yr^1
coincident observations of gravitational-wave mergers with gamma-ray
burst prompt emission, 13^+23 _10 yr^1 detections with kilonova
observations, and 4^+18 _3 yr^1 with broadband afterglows and
kilonovae, where the uncertainties are 90% confidence intervals arising
from uncertainty in current merger-rate estimates. Combined, this
implies a coincident detection rate of 14^+25 _11 yr^1 out to 300Mpc.
These numbers indicate significant science potential for a single
kilohertz gravitational-wave detector operating without a global network
of other gravitational-wave observatories.
----------------------------------------------------------------
arXiv:2110.13319 gr-qc astro-ph.CO astro-ph.HE
*Did Goryachev et al. detect megahertz gravitational waves? *
*Authors*: Paul D. Lasky, Eric Thrane
Abstract: Goryachev et al. [1] recently announced the detection of "two
strongly significant events" in their Bulk Acoustic Wave High Frequency
Gravitational Wave Antenna. They claim many possibilities for the cause
of these events, including high-frequency megahertz gravitational waves.
We demonstrate these events are not due to gravitational waves for two
reasons. 1) The inferred stochastic gravitational-wave background from
these events implies the gravitational-wave energy density of the
Universe is _gw 10^8 , approximately 10^8 times the closure density of
the Universe. 2) The low-frequency gravitational-wave memory signal that
accompanies any high-frequency gravitational-wave source visible by the
current generation of high-frequency detectors would have been visible
by LIGO/Virgo as a transient burst with signal-to-noise ratio 10^6 .
The non-detection of such loud memory bursts throughout the operation of
LIGO/Virgo rules out the gravitational-wave explanation for the
high-frequency events detected by Goryachev et al. We discuss broader
implications of this work for the ongoing experimental search for ultra
high-frequency (MHz-GHz) gravitational waves.
Journal reference: Physical Review D 104, 103017 (2021)
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arXiv:2102.12028 gr-qc
*Cylindrical spikes *
*Authors*: Muhammad Zubair Ali Moughal, Woei Chet Lim
Abstract: The Geroch/Stephani transformation is a solution-generating
transformation, and may generate spiky solutions. The spikes in
solutions generated so far are either early-time permanent spikes or
transient spikes. We want to generate a solution with a late-time
permanent spike. We achieve this by applying Stephani's transformation
with the rotational Killing vector field of the locally rotationally
symmetric Jacobs solution. The late-time permanent spike occurs along
the cylindrical axis. Using a mixed Killing vector field, the generated
solution also features a rich variety of transient structures. We
introduce a new technique to analyse these structures. Our findings lead
us to discover a transient behaviour, which we call the overshoot
transition. These discoveries compel us to revise the description of
transient spikes.
Journal reference: Class. Quantum Grav. 38 (2021) 075029
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arXiv:2111.15122 gr-qc
*Transition analysis of the non-OT G2 stiff fluid spike solution *
*Authors*: Woei Chet Lim, Muhammad Zubair Ali Moughal
Abstract: We use the technique developed in Moughal's doctoral thesis to
analyse the joint spike transition, revealing new groups of worldlines
which undergo distinct transitions, and correcting misconceptions about
spikes.
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arXiv:2102.13551 gr-qc
*Hawking-Ellis classification of stress-energy: test-fields versus
back-reaction *
*Authors*: Prado Martin-Moruno, Matt Visser
Abstract: We consider the Hawking-Ellis (Segre-Plebanski) classification
of stress-energy tensors, both in the test-field limit, and in the
presence of back-reaction governed by the usual Einstein equations. For
test fields it is not too difficult to get a type~IV stress-energy via
quantum vacuum polarization effects. (For example, consider the Unruh
quantum vacuum state for a massless scalar field in the Schwarzschild
background.) However, in the presence of back-reaction driven by the
ordinary Einstein equations the situation is often much more
constrained. For instance: (1) in any static spacetime the stress-energy
is always type I in the domain of outer communication, and on any
horizon that might be present; (2) in any stationary axisymmetric
spacetime the stress-energy is always type I on any horizon that might
be present; (3) on any Killing horizon that is extendable to a
bifurcation 2-surface the stress-energy is always type I; (4) in any
stationary axisymmetric spacetime the stress-energy is always type I on
the axis of symmetry; (5) some of the homogeneous Bianchi cosmologies
are guaranteed to be Hawking-Ellis type I (for example, all the Bianchi
type I cosmologies, all the FLRW cosmologies, and all the "single mode"
Bianchi cosmologies). That is, in very many physically interesting
situations once one includes back-reaction the more unusual
stress-energy types are automatically excluded.
Journal reference: Phys. Rev. D 103, 124003 (2021)
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arXiv:2103.12786 gr-qc
*The little rip in classical and quantum f(R) cosmology *
*Authors*: Teodor Borislavov Vasilev, Mariam Bouhmadi-López, Prado
Martín-Moruno
Abstract: The little rip is a cosmological abrupt event predicted by
some phantom dark energy models that could describe the future evolution
of our Universe. This event can be interpreted as a big rip singularity
delayed indefinitely, although in those models bounded structures will
be destroyed in a finite cosmic time in the future. In this work, we
analyse the little rip cosmology from a classical and quantum point of
view within the scheme of alternative metric f(R) theories of gravity.
The quantum analysis is performed in the framework of f(R) quantum
geometrodynamics by means of the modified Wheeler-DeWitt equation. In
this context, we show that the DeWitt criterion can be satisfied.
Similar to what happens in general relativity, this result points
towards the avoidance of the little rip in f(R) quantum cosmology.
Journal reference: Phys. Rev. D 103, 124049 (2021)
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arXiv:2105.12582 gr-qc
*Modified Gravity and Cosmology: An Update by the CANTATA Network *
*Authors*: Emmanuel N. Saridakis, Ruth Lazkoz, Vincenzo Salzano, Paulo
Vargas Moniz, Salvatore Capozziello, Jose Beltrán Jiménez, Mariafelicia
De Laurentis, Gonzalo J. Olmo, Yashar Akrami, Sebastian Bahamonde, Jose
Luis Blázquez-Salcedo, Christian G. Böhmer, Camille Bonvin, Mariam
Bouhmadi-López, Philippe Brax, Gianluca Calcagni, Roberto Casadio, Jose
A. R. Cembranos, Álvaro de la Cruz-Dombriz, Anne-Christine Davis, Adrià
Delhom, Eleonora Di Valentino, Konstantinos F. Dialektopoulos, Benjamin
Elder, Jose María Ezquiaga , et al. (28 additional authors not shown)
Abstract: General Relativity and the CDM framework are currently the
standard lore and constitute the concordance paradigm. Nevertheless,
long-standing open theoretical issues, as well as possible new
observational ones arising from the explosive development of cosmology
the last two decades, offer the motivation and lead a large amount of
research to be devoted in constructing various extensions and
modifications. All extended theories and scenarios are first examined
under the light of theoretical consistency, and then are applied to
various geometrical backgrounds, such as the cosmological and the
spherical symmetric ones. Their predictions at both the background and
perturbation levels, and concerning cosmology at early, intermediate and
late times, are then confronted with the huge amount of observational
data that astrophysics and cosmology are able to offer recently.
Theories, scenarios and models that successfully and efficiently pass
the above steps are classified as viable and are candidates for the
description of Nature. We list the recent developments in the fields of
gravity and cosmology, presenting the state of the art, high-lighting
the open problems, and outlining the directions of future research. Its
realization is performed in the framework of the COST European Action
"Cosmology and Astrophysics Network for Theoretical Advances and
Training Actions".
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arXiv:2106.12050 gr-qc astro-ph.CO hep-th
*Classical and quantum f(R) cosmology: The big rip, the little rip and
the little sibling of the big rip *
*Authors*: Teodor Borislavov Vasilev, Mariam Bouhmadi-López, Prado
Martín-Moruno
Abstract: The big rip, the little rip and the little sibling of the big
rip are cosmological doomsdays predicted by some phantom dark energy
models that could describe the future evolution of our Universe. When
the universe evolves towards either of these future cosmic events all
bounded structures and, ultimately, space-time itself are ripped apart.
Nevertheless, it is commonly belief that quantum gravity effects may
smooth or even avoid these classically predicted singularities. In this
review, we discuss the classical and quantum occurrence of these riplike
events in the scheme of metric f(R) theories of gravity. The quantum
analysis is performed in the framework of f(R) quantum geometrodynamics.
In this context, we analyse the fulfilment of the DeWitt criterion for
the avoidance of these singular fates.
Journal reference: Universe 7 (2021) no.8, 288
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arXiv:2111.05659 hep-ph astro-ph.HE gr-qc hep-th
*Quantum gravity phenomenology at the dawn of the multi-messenger era --
A review *
*Authors*: A. Addazi, J. Alvarez-Muniz, R. Alves Batista, G.
Amelino-Camelia, V. Antonelli, M. Arzano, M. Asorey, J. -L. Atteia, S.
Bahamonde, F. Bajardi, A. Ballesteros, B. Baret, D. M. Barreiros, S.
Basilakos, D. Benisty, O. Birnholtz, J. J. Blanco-Pillado, D. Blas, J.
Bolmont, D. Boncioli, P. Bosso, G. Calcagni, S. Capozziello, J. M.
Carmona, S. Cerci , et al. (135 additional authors not shown)
Abstract: The exploration of the universe has recently entered a new era
thanks to the multi-messenger paradigm, characterized by a continuous
increase in the quantity and quality of experimental data that is
obtained by the detection of the various cosmic messengers (photons,
neutrinos, cosmic rays and gravitational waves) from numerous origins.
They give us information about their sources in the universe and the
properties of the intergalactic medium. Moreover, multi-messenger
astronomy opens up the possibility to search for phenomenological
signatures of quantum gravity. On the one hand, the most energetic
events allow us to test our physical theories at energy regimes which
are not directly accessible in accelerators; on the other hand, tiny
effects in the propagation of very high energy particles could be
amplified by cosmological distances. After decades of merely theoretical
investigations, the possibility of obtaining phenomenological
indications of Planck-scale effects is a revolutionary step in the quest
for a quantum theory of gravity, but it requires cooperation between
different communities of physicists (both theoretical and experimental).
This review is aimed at promoting this cooperation by giving a
state-of-the art account of the interdisciplinary expertise that is
needed in the effective search of quantum gravity footprints in the
production, propagation and detection of cosmic messengers.
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arXiv:2111.06986 gr-qc astro-ph.HE astro-ph.IM
*Expanding the Reach of Gravitational Wave Astronomy to the Edge of the
Universe: The Gravitational-Wave International Committee Study Reports
on Next Generation Ground-based Gravitational-Wave Observatories *
*Authors*: David Reitze, Michele Punturo, Peter Couvares, Stavros
Katsanevas, Takaaki Kajita, Vicky Kalogera, Harald Lueck, David
McClelland, Sheila Rowan, Gary Sanders, B. S. Sathyaprakash, David
Shoemaker, Jo van den Brand
Abstract: The first direct detection of gravitational waves emitted from
a pair of merging black holes in 2015 has been heralded as one of most
significant scientific breakthroughs in physics and astronomy of the
21st century. Motivated by the tremendous scientific opportunities now
opened by gravitational-wave observatories and recognizing that to fully
exploit the new field will require new observatories that may take 15 to
20 years from conception until operations begin, the Gravitational Wave
International Committee (GWIC) convened a subcommittee to examine the
path to build and operate a network of future ground-based
observatories, capable of extending the observational GW horizon well
beyond that currently attainable with the current generation of
detectors. This report is the first in a six part series of reports by
the GWIC 3G Subcommittee: i) Expanding the Reach of Gravitational Wave
Observatories to the Edge of the Universe (this report), ii) The Next
Generation Global Gravitational Wave Observatory: The Science Book, iii)
3G R&D: R&D for the Next Generation of Ground-based Gravitational Wave
Detectors, iv) Gravitational Wave Data Analysis: Computing Challenges in
the 3G Era, v) Future Ground-based Gravitational-wave Observatories:
Synergies with Other Scientific Communities, and vi) An Exploration of
Possible Governance Models for the Future Global Gravitational-Wave
Observatory Network.
----------------------------------------------------------------
arXiv:2111.06987 gr-qc astro-ph.HE astro-ph.IM
*Gravitational Wave Data Analysis: Computing Challenges in the 3G Era *
*Authors*: Peter Couvares, Ian Bird, Ed Porter, Stefano Bagnasco,
Michele Punturo, David Reitze, Stavros Katsanevas, Takaaki Kajita, Vicky
Kalogera, Harald Lueck, David McClelland, Sheila Rowan, Gary Sanders, B.
S. Sathyaprakash, David Shoemaker, Jo van den Brand
Abstract: Cyber infrastructure will be a critical consideration in the
development of next generation gravitational-wave detectors. The demand
for data analysis computing in the 3G era will be driven by the high
number of detections as well as the expanded search parameter space for
compact astrophysical objects and the subsequent parameter estimation
follow-up required to extract the nature of the sources. Additionally,
there will be an increased need to develop appropriate and scalable
computing cyberinfrastructure, including data access and transfer
protocols, and storage and management of software tools, that have
sustainable development, support, and management processes. This report
identifies the major challenges and opportunities facing 3G
gravitational-wave observatories and presents recommendations for
addressing them. This report is the fourth in a six part series of
reports by the GWIC 3G Subcommittee: i) Expanding the Reach of
Gravitational Wave Observatories to the Edge of the Universe, ii) The
Next Generation Global Gravitational Wave Observatory: The Science Book,
iii) 3G R&D: R&D for the Next Generation of Ground-based Gravitational
Wave Detectors, iv) Gravitational Wave Data Analysis: Computing
Challenges in the 3G Era (this report), v) Future Ground-based
Gravitational-wave Observatories: Synergies with Other Scientific
Communities, and vi) An Exploration of Possible Governance Models for
the Future Global Gravitational-Wave Observatory Network.
----------------------------------------------------------------
arXiv:2111.06988 gr-qc astro-ph.HE astro-ph.IM
*Future Ground-Based Gravitational-Wave Observatories: Synergies with
Other Scientific Communities *
*Authors*: Michele Punturo, David Reitze, Peter Couvares, Stavros
Katsanevas, Takaaki Kajita, Vicky Kalogera, Harald Lueck, David
McClelland, Sheila Rowan, Gary Sanders, B. S. Sathyaprakash, David
Shoemaker, Jo van den Brand
Abstract: Planning for the development of a 3rd generation global
gravitational-wave detector array is a multifaceted and complex effort
that will necessarily need a high level of community input. Interfacing
to extant and new stakeholders in the broader scientific constituencies
is necessary to keep them aware of the activities taking place in the
ground-based gravitational-wave community and receive input to inform
and evolve the planning. In this report, we present the approaches GWIC
and gravitational-wave collaborations and projects should consider
taking to engage with broader community. This report is the fifth in a
six part series of reports by the GWIC 3G Subcommittee: i) Expanding the
Reach of Gravitational Wave Observatories to the Edge of the Universe,
ii) The Next Generation Global Gravitational Wave Observatory: The
Science Book, iii) 3G R&D: R&D for the Next Generation of Ground-based
Gravitational Wave Detectors, iv) Gravitational Wave Data Analysis:
Computing Challenges in the 3G Era, v) Future Ground-based
Gravitational-wave Observatories: Synergies with Other Scientific
Communities (this report), and vi) An Exploration of Possible Governance
Models for the Future Global Gravitational-Wave Observatory Network.
----------------------------------------------------------------
arXiv:2111.06989 gr-qc astro-ph.HE astro-ph.IM
*An Exploration of Possible Governance Models for the Future Global
Gravitational-Wave Observatory Network *
*Authors*: Stavros Katsanevas, Gary Sanders, Beverly Berger, Gabriela
González, James Hough, Ajit K. Kembhavi, David McClelland, Masatake
Ohashi, Fulvio Ricci, Stan Whitcomb, Michele Punturo, David Reitze,
Peter Couvares, Takaaki Kajita, Vicky Kalogera, Harald Lueck, David
McClelland, Sheila Rowan, B. S. Sathyaprakash, David Shoemaker, Jo van
den Brand
Abstract: The construction of a global network of detectors is the
cornerstone to scientific success for 3rd generation gravitational wave
astronomy. If carried out with a vision to the future, the third
generation implementation, in its infrastructure, technology base and
governance can provide the point of departure for subsequent
developments beyond the third generation, a path to the long and
revolutionary future of gravitational wave astrophysics. The goal of
this document is to lay out considerations that influence the optimal
choice of governance and to lay out a possible path that can lead the
community to an optimal governance model. This report is the six in a
six part series of reports by the GWIC 3G Subcommittee: i) Expanding the
Reach of Gravitational Wave Observatories to the Edge of the Universe,
ii) The Next Generation Global Gravitational Wave Observatory: The
Science Book, iii) 3G R&D: R&D for the Next Generation of Ground-based
Gravitational Wave Detectors, iv) Gravitational Wave Data Analysis:
Computing Challenges in the 3G Era, v) Future Ground-based
Gravitational-wave Observatories: Synergies with Other Scientific
Communities, and vi) An Exploration of Possible Governance Models for
the Future Global Gravitational-Wave Observatory Network (this report).
----------------------------------------------------------------
arXiv:2111.06990 gr-qc
*The Next Generation Global Gravitational Wave Observatory: The Science
Book *
*Authors*: Vicky Kalogera, B. S. Sathyaprakash, Matthew Bailes,
Marie-Anne Bizouard, Alessandra Buonanno, Adam Burrows, Monica Colpi,
Matt Evans, Stephen Fairhurst, Stefan Hild, Mansi M. Kasliwal, Luis
Lehner, Ilya Mandel, Vuk Mandic, Samaya Nissanke, Maria Alessandra Papa,
Sanjay Reddy, Stephan Rosswog, Chris Van Den Broeck, P. Ajith, Shreya
Anand, Igor Andreoni, K. G. Arun, Enrico Barausse, Masha Baryakhtar , et
al. (66 additional authors not shown)
Abstract: The next generation of ground-based gravitational-wave
detectors will observe coalescences of black holes and neutron stars
throughout the cosmos, thousands of them with exceptional fidelity. The
Science Book is the result of a 3-year effort to study the science
capabilities of networks of next generation detectors. Such networks
would make it possible to address unsolved problems in numerous areas of
physics and astronomy, from Cosmology to Beyond the Standard Model of
particle physics, and how they could provide insights into workings of
strongly gravitating systems, astrophysics of compact objects and the
nature of dense matter. It is inevitable that observatories of such
depth and finesse will make new discoveries inaccessible to other
windows of observation. In addition to laying out the rich science
potential of the next generation of detectors, this report provides
specific science targets in five different areas in physics and
astronomy and the sensitivity requirements to accomplish those science
goals. This report is the second in a six part series of reports by the
GWIC 3G Subcommittee: i) Expanding the Reach of Gravitational Wave
Observatories to the Edge of the Universe, ii) The Next Generation
Global Gravitational Wave Observatory: The Science Book (this report),
iii) 3G R&D: R&D for the Next Generation of Ground-based Gravitational
Wave Detectors, iv) Gravitational Wave Data Analysis: Computing
Challenges in the 3G Era, v) Future Ground-based Gravitational-wave
Observatories: Synergies with Other Scientific Communities, and vi) An
Exploration of Possible Governance Models for the Future Global
Gravitational-Wave Observatory Network.
----------------------------------------------------------------
arXiv:2111.06991 gr-qc
*3G R&D: R&D for the Next Generation of Ground-based Gravitational-wave
Detectors *
*Authors*: David McClelland, Harald Lueck, Rana Adhikari, Masaki Ando,
GariLynn Billingsley, Geppo Cagnoli, Matt Evans, Martin Fejer, Andreas
Freise, Paul Fulda, Eric Genin, Gabriela González, Jan Harms, Stefan
Hild, Giovanni Losurdo, Ian Martin, Anil Prabhakar, Stuart Reid, Fulvio
Ricci, Norna Robertson, Jo van den Brand, Benno Willke, Michael Zucker,
Alessandro Bertolini, Stefan Danilishin , et al. (21 additional authors
not shown)
Abstract: To deliver on the promise of next generation
gravitational-wave observatories, a sustained and coordinated detector
research and development program is required. This report examines in
detail the wide range of nearer- and longer-term detector R&D programs
needed for next generation GW detectors commensurate with the key
science targets presented in "The Next Generation Global Gravitational
Wave Observatory: The Science Book", including considerations of site
selection and large-scale vacuum infrastructure. The report makes a
series of detailed recommendations on the needed advances in detector
technology and the timescales needed to achieve those advances. It also
identifies areas where larger-scale globally coordinated R&D efforts
will be critical to ensuring success while minimizing costs. This report
is the third in a six part series of reports by the GWIC 3G
Subcommittee: i) Expanding the Reach of Gravitational Wave Observatories
to the Edge of the Universe, ii) The Next Generation Global
Gravitational Wave Observatory: The Science Book, iii) 3G R&D: R&D for
the Next Generation of Ground-based Gravitational Wave Detectors (this
report), iv) Gravitational Wave Data Analysis: Computing Challenges in
the 3G Era, v) Future Ground-based Gravitational-wave Observatories:
Synergies with Other Scientific Communities, and vi) An Exploration of
Possible Governance Models for the Future Global Gravitational-Wave
Observatory Network.
----------------------------------------------------------------
arXiv:2003.08588 gr-qc astro-ph.HE astro-ph.IM
*Search for gravitational waves from twelve young supernova remnants
with a hidden Markov model in Advanced LIGO's second observing run *
*Authors*: Margaret Millhouse, Lucy Strang, Andrew Melatos
Abstract: Persistent gravitational waves from rapidly rotating neutron
stars, such as those found in some young supernova remnants, may fall in
the sensitivity band of the advanced Laser Interferometer
Gravitational-wave Observatory (aLIGO). Searches for these signals are
computationally challenging, as the frequency and frequency derivative
are unknown and evolve rapidly due to the youth of the source. A hidden
Markov model (HMM), combined with a maximum-likelihood matched filter,
tracks rapid frequency evolution semi-coherently in a computationally
efficient manner. We present the results of an HMM search targeting 12
young supernova remnants in data from Advanced LIGO's second observing
run. Six targets produce candidates that are above the search threshold
and survive pre-defined data quality vetoes. However, follow-up analyses
of these candidates show that they are all consistent with instrumental
noise artefacts.
Journal reference: Phys. Rev. D 102, 083025 (2020)
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arXiv:2006.06907 astro-ph.HE astro-ph.IM gr-qc
*Search for gravitational waves from five low mass X-ray binaries in the
second Advanced LIGO observing run with an improved hidden Markov model *
*Authors*: Hannah Middleton, Patrick Clearwater, Andrew Melatos, Liam Dunn
Abstract: Low mass X-ray binaries are prime targets for continuous
gravitational wave searches by ground-based interferometers. Results are
presented from a search for five low-mass X-ray binaries whose spin
frequencies and orbital elements are measured accurately from X-ray
pulsations: HETE J1900.1-2455, IGR J00291+5934, SAX J1808.4-3658, XTE
J0929-314, and XTE J1814-338. Data are analysed from Observing Run 2 of
the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO).
The search algorithm uses a hidden Markov model to track spin wandering,
the J-statistic maximum likelihood matched filter to track orbital
phase, and a suite of five vetoes to reject artefacts from non-Gaussian
noise. The search yields a number of low-significance, above threshold
candidates consistent with the selected false-alarm probability. The
candidates will be followed up in subsequent observing runs.
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arXiv:2102.06334 astro-ph.HE gr-qc
*Search for continuous gravitational waves from ten H.E.S.S. sources
using a hidden Markov model *
*Authors*: Deeksha Beniwal, Patrick Clearwater, Liam Dunn, Andrew
Melatos, David Ottaway
Abstract: Isolated neutron stars are prime targets for continuous-wave
(CW) searches by ground-based gravitationalwave interferometers.
Results are presented from a CW search targeting ten pulsars. The search
uses a semicoherent algorithm, which combines the maximum-likelihood
F-statistic with a hidden Markov model (HMM) to efficiently detect and
track quasimonochromatic signals which wander randomly in frequency.
The targets, which are associated with TeV sources detected by the High
Energy Stereoscopic System (H.E.S.S.), are chosen to test for
gravitational radiation from young, energetic pulsars with strong -ray
emission, and take maximum advantage of the frequency tracking
capabilities of HMM compared to other CW search algorithms. The search
uses data from the second observing run of the Advanced Laser
Interferometer Gravitational-Wave Observatory (aLIGO). It scans 1Hz
sub-bands around f_ , 4f_ /3, and 2f_ , where f_ denotes the star's
rotation frequency, in order to accommodate a physically plausible
frequency mismatch between the electromagnetic and gravitational-wave
emission. The 24 sub-bands searched in this study return 5,256
candidates above the Gaussian threshold with a false alarm probability
of 1% per sub-band per target. Only 12 candidates survive the three data
quality vetoes which are applied to separate nonGaussian artifacts from
true astrophysical signals. CW searches using the data from subsequent
observing runs will clarify the status of the remaining candidates.
Journal reference: Phys.Rev.D 103 (2021) 083009
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arXiv:2102.10816 gr-qc
*Enhancing gravitational-wave burst detection confidence in expanded
detector networks with the BayesWave pipeline *
*Authors*: Yi Shuen C. Lee, Margaret Millhouse, Andrew Melatos
Abstract: The global gravitational-wave detector network achieves higher
detection rates, better parameter estimates, and more accurate sky
localisation, as the number of detectors, I increases. This paper
quantifies network performance as a function of I for BayesWave, a
source-agnostic, wavelet-based, Bayesian algorithm which distinguishes
between true astrophysical signals and instrumental glitches. Detection
confidence is quantified using the signal-to-glitch Bayes factor, B_S,G
. An analytic scaling is derived for B_S,G versus I, the number of
wavelets, and the network signal-to-noise ratio, SNR_net , which is
confirmed empirically via injections into detector noise of the
Hanford-Livingston (HL), Hanford-Livingston-Virgo (HLV), and
Hanford-Livingston-KAGRA-Virgo (HLKV) networks at projected
sensitivities for the fourth observing run (O4). The empirical and
analytic scalings are consistent; B_S,G increases with I. The accuracy
of waveform reconstruction is quantified using the overlap between
injected and recovered waveform, O_net . The HLV and HLKV network
recovers 87% and 86% of the injected waveforms with O_net >0.8
respectively, compared to 81% with the HL network. The accuracy of
BayesWave sky localisation is 10 times better for the HLV network than
the HL network, as measured by the search area, A, and the sky areas
contained within 50% and 90% confidence intervals. Marginal improvement
in sky localisation is also observed with the addition of KAGRA.
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arXiv:2103.12976 gr-qc
*Deep exploration for continuous gravitational waves at 171--172 Hz in
LIGO second observing run data *
*Authors*: Karl Wette, Liam Dunn, Patrick Clearwater, Andrew Melatos
Abstract: We pursue a novel strategy towards a first detection of
continuous gravitational waves from rapidly-rotating deformed neutron
stars. Computational power is focused on a narrow region of signal
parameter space selected by a strategically-chosen benchmark. We search
data from the 2nd observing run of the LIGO Observatory with an
optimised analysis run on graphics processing units. While no continuous
waves are detected, the search achieves a sensitivity to gravitational
wave strain of h_0 =1.01×10^25 at 90% confidence, 24% to 69% better
than past searches of the same parameter space. Constraints on neutron
star deformity are within theoretical maxima, thus a detection by this
search was not inconceivable.
Journal reference: Physical Review D 103, 083020 (2021)
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arXiv:2107.12822 gr-qc
*Hidden Markov model tracking of continuous gravitational waves from a
neutron star with wandering spin. III. Rotational phase tracking *
*Authors*: A. Melatos, P. Clearwater, S. Suvorova, L. Sun, W. Moran, R.
J. Evans
Abstract: A hidden Markov model (HMM) solved recursively by the Viterbi
algorithm can be configured to search for persistent, quasimonochromatic
gravitational radiation from an isolated or accreting neutron star,
whose rotational frequency is unknown and wanders stochastically. Here
an existing HMM analysis pipeline is generalized to track rotational
phase and frequency simultaneously, by modeling the intra-step
rotational evolution according to a phase-wrapped Ornstein-Uhlenbeck
process, and by calculating the emission probability using a
phase-sensitive version of the Bayesian matched filter known as the
B-statistic. The generalized algorithm tracks signals from isolated and
binary sources with characteristic wave strain h_0 1.3×10^26 in
Gaussian noise with amplitude spectral density 4×10^24 Hz^1/2 , for a
simulated observation composed of N_T =37 data segments, each T_drift
=10days long, the typical duration of a search for the low-mass X-ray
binary (LMXB) Sco X1 with the Laser Interferometer Gravitational Wave
Observatory (LIGO). It is equally sensitive to isolated and binary
sources and 1.5 times more sensitive than the previous pipeline.
Receiver operating characteristic curves and errors in the recovered
parameters are presented for a range of practical h_0 and N_T values.
The generalized algorithm successfully detects every available synthetic
signal in Stage I of the Sco X1 Mock Data Challenge convened by the
LIGO Scientific Collaboration, recovering the frequency and orbital
semimajor axis with accuracies of better than 9.5×10^7 Hz and 1.6×10^3
lts respectively. The Viterbi solver runs in 2×10^3 CPU-hr for an
isolated source and 10^5 CPU-hr for a LMXB source in a typical,
broadband (0.5-kHz) search.
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arXiv:2108.11338 gr-qc
*Scalar perturbations of Galileon cosmologies in the mechanical approach
within the late Universe *
*Authors*: Jan Novák
Abstract: We investigate the Universe at the late stage of its evolution
and inside the cell of uniformity 150-370 Mpc. We consider the Universe
to be filled at these scales with dust like matter, a minimally coupled
Galileon field and radiation. We use the mechanical approach. Therefore,
the peculiar velocities of the inhomogeneities as well as the
fluctuations of the other perfect fluids can be considered
nonrelativistic. Such fluids are said to be coupled because they are
concentrated around the inhomogeneities. We investigate the conditions
under which the physical Galileon field, i.e. compatible with results of
the latest gravitational wave experiments GW150914, GW151226, GW170104,
GW170814, GW170817 and GW170608, can become coupled. We know that at the
background level coupled scalar fields behave as a two-component perfect
fluids: one which mimics a network of frustrated cosmic string and an
another one which corresponds to an effective cosmological constant. We
found a correction for the Galileon field, which behaves like a matter
component.
Journal reference: Gravitation and Cosmology, 2020, Vol.26, No.4, pp.
351-357
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arXiv:2002.02119 gr-qc math.AP
*Stabilizing relativistic fluids on spacetimes with non-accelerated
expansion *
*Authors*: David Fajman, Todd A. Oliynyk, Zoe Wyatt
Abstract: We establish global regularity and stability for the
irrotational relativistic Euler equations with equation of state p¯=K¯,
where 02 are non-linearly stable, and all
sufficiently small perturbations exhibit asymptotically velocity term
dominated (AVTD) behavior and blow-up of the Kretschmann scalar.
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arXiv:2108.02886 gr-qc math.AP
*Stability of Asymptotic Behavior Within Polarised T^2 -Symmetric Vacuum
Solutions with Cosmological Constant *
*Authors*: Ellery Ames, Florian Beyer, James Isenberg, Todd Oliynyk
Abstract: We prove the nonlinear stability of the asymptotic behavior of
perturbations of subfamilies of Kasner solutions in the contracting time
direction within the class of polarised T^2 -symmetric solutions of the
vacuum Einstein equations with arbitrary cosmological constant . This
stability result generalizes the results proven in [3], which focus on
the =0 case, and as in that article, the proof relies on an areal time
foliation and Fuchsian techniques. Even for =0, the results established
here apply to a wider class of perturbations of Kasner solutions within
the family of polarised T^2 -symmetric vacuum solutions than those
considered in [3] and [26]. Our results establish that the areal time
coordinate takes all values in (0,T_0 ] for some T_0 >0, for certain
families of polarised T^2 -symmetric solutions with cosmological constant.
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arXiv:1912.02173 gr-qc astro-ph.CO
*Black Hole Genesis and origin of cosmic acceleration *
*Authors*: Nikodem J. Popawski
Abstract: We consider a hypothesis that the closed Universe was formed
on the other side of the event horizon of a black hole existing in
another universe. That black hole appears in the Universe as a boundary
white hole, and its rest frame in comoving coordinates is a frame of
reference in which the cosmic microwave background is isotropic. We
consider the Lagrangian density for the gravitational field that is
proportional to the curvature scalar, and use the metric-affine
variational principle in which the symmetric affine connection and the
metric tensor are variables. The white hole appears in the Lagrangian
through a simplest, generally covariant and linear term: the
four-divergence of the four-velocity of the white hole in comoving
coordinates. We show that the variation of the action with respect to
the connection generates the nonmetricity, which creates a term in the
Lagrangian that is equivalent to a positive cosmological constant. The
current cosmic acceleration may therefore be a manifestation of the
boundary of the closed Universe. We also show that the equation of
motion of a test particle deviates from the geodesic equation by a term
that depends on the four-velocities of the particle and the white hole.
The rest frame of the white hole in comoving coordinates is the only
absolutely inertial frame of reference. This deviation might be observed
on galactic scales.
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arXiv:2007.11556 gr-qc astro-ph.CO
*The universe as a closed anisotropic universe born in a black hole *
*Authors*: Nikodem Popawski
Abstract: We consider a universe formed in a black hole in the
Einstein--Cartan theory of gravity. The interior of a Schwarzschild
black hole can be represented by the Kantowski--Sachs metric that
describes a closed anisotropic universe. We use this metric to derive
the field equations with a relativistic spin fluid as a source. We show
that torsion may prevent a singularity and replace it with a nonsingular
bounce if particle production dominates over shear. Particle production
after the last bounce can generate a finite period of inflation, during
which the universe expands and isotropizes to the currently observed
state. Our universe might have therefore originated from a black hole.
Journal reference: Gen. Relativ. Gravit. 53, 18 (2021)
----------------------------------------------------------------
arXiv:2008.02136 gr-qc astro-ph.CO
*Gravitational collapse of a fluid with torsion into a universe in a
black hole *
*Authors*: Nikodem Popawski
Abstract: We consider gravitational collapse of a spherically symmetric
sphere of a fluid with spin and torsion into a black hole. We use the
Tolman metric and the Einstein--Cartan field equations with a
relativistic spin fluid as a source. We show that gravitational
repulsion of torsion prevents a singularity and replaces it with a
nonsingular bounce. Quantum particle production during contraction helps
torsion to dominate over shear. Particle production during expansion can
generate a finite period of inflation and produce enormous amounts of
matter. The resulting closed universe on the other side of the event
horizon may have several bounces. Such a universe is oscillatory, with
each cycle larger in size then the previous cycle, until it reaches the
cosmological size and expands indefinitely. Our universe might have
therefore originated from a black hole.
Journal reference: Zh. Eksp. Teor. Fiz. 159, 448 (2021)
----------------------------------------------------------------
arXiv:2101.04212 gr-qc quant-ph
*Relativistic wave--particle duality for spinors *
*Authors*: Nikodem Popawski
Abstract: We propose that relativistic wave--particle duality can be
embodied in a relation u^i =¯^i /¯, which determines the mean
four-velocity of the fermion particle associated with a Dirac wave
function. We use the Einstein--Cartan theory of gravity with torsion,
which incorporates the spin-orbit interaction in curved spacetime. This
relation is satisfied by a spinor plane wave and it is consistent with
the energy-momentum tensor for particles. We suggest that spacetime
guides the evolution of a wave function, that in turn guides the mean
motion of the associated particle. Consequently, spacetime guides the
motion of particles. The exact motion is limited by the uncertainty
principle.
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arXiv:2107.01612 hep-th gr-qc
*Torsional Regularization of Self-Energy and Bare Mass of Electron *
*Authors*: Michael Del Grosso, Nikodem Popawski
Abstract: In the presence of spacetime torsion, the momentum components
do not commute; therefore, in quantum field theory, summation over the
momentum eigenvalues will replace integration over the momentum. In the
Einstein--Cartan theory of gravity, in which torsion is coupled to spin,
the separation between the eigenvalues increases with the magnitude of
the momentum. Consequently, this replacement regularizes divergent
integrals in Feynman diagrams with loops by turning them into convergent
sums. In this article, we apply torsional regularization to the
self-energy of a charged lepton in quantum electrodynamics. We show that
this procedure eliminates the ultraviolet divergence. We also show that
torsion gives a photon a small nonzero mass, which regularizes the
infrared divergence. In the end, we calculate the finite bare masses of
the electron, muon, and tau lepton: 0.4329MeV, 90.95MeV, and 1543MeV,
respectively. These values constitute about 85% of the observed,
re-normalized masses.
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arXiv:2102.07353 astro-ph.IM
*SkyMapper Optical Follow-up of Gravitational Wave Triggers: Alert
Science Data Pipeline and LIGO/Virgo O3 Run *
*Authors*: Seo-Won Chang, Christopher A. Onken, Christian Wolf, Lance
Luvaul, Anais Möller, Richard Scalzo, Brian P. Schmidt, Susan M. Scott,
Nikunj Sura, Fang Yuan
Abstract: We present an overview of the SkyMapper optical follow-up
program for gravitational-wave event triggers from the LIGO/Virgo
observatories, which aims at identifying early GW170817-like kilonovae
out to 200 Mpc distance. We describe our robotic facility for rapid
transient follow-up, which can target most of the sky at <+10° to a
depth of iAB20 mag. We have implemented a new software pipeline to
receive LIGO/Virgo alerts, schedule observations and examine the
incoming real-time data stream for transient candidates. We adopt a
real-bogus classifier using ensemble-based machine learning techniques,
attaining high completeness (98%) and purity (91%) over our whole
magnitude range. Applying further filtering to remove common image
artefacts and known sources of transients, such as asteroids and
variable stars, reduces the number of candidates by a factor of more
than 10. We demonstrate the system performance with data obtained for
GW190425, a binary neutron star merger detected during the LIGO/Virgo O3
observing campaign. In time for the LIGO/Virgo O4 run, we will have
deeper reference images allowing transient detection to iAB21 mag.
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arXiv:2103.15984 gr-qc
*The Endpoint Theorem *
*Authors*: Susan M Scott, Ben E Whale
Abstract: The Endpoint Theorem links the existence of a sequence
(curve), without accumulation points, in a manifold to the existence of
an open embedding of that manifold so that the image of the given
sequence (curve) has a unique endpoint. It plays a fundamental role in
the theory of the Abstract Boundary as it implies that there is always
an Abstract Boundary boundary point to represent the endpoint of such
sequences and curves. The Endpoint Theorem will be of interest to
researchers analysing specific spacetimes as it shows how to construct a
chart in the original manifold which contains the sequence (curve). In
particular, it has application to the study of singularities predicted
by the singularity theorems.
Journal reference: Class. Quantum Grav. 38 065012 (2021)
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arXiv:2110.10870 gr-qc
*Enhanced Frequency noise suppression for LISA by combining cavity and
arm locking control systems *
*Authors*: Jobin Thomas Valliyakalayil, Andrew J. H. Sutton, Robert E.
Spero, Daniel A. Shaddock, Kirk McKenzie
Abstract: This paper presents a novel method for laser frequency
stabilisation in the Laser Interferometer Space Antenna (LISA) mission
by locking a laser to two stable length references - the arms of the
interferometer and an on-board optical cavity. The two references are
digitally fused using carefully designed control systems, ensuring no
changes to the baseline LISA mission hardware are required. The
interferometer arm(s) provides the most stable reference available in
the LISA science band (0.1 mHz - 1 Hz), while the cavity sensor's
wide-band and linear readout enables additional control system gain
below and above the LISA band. The main technical issue with this dual
sensor approach is the undesirable slow laser frequency pulling which
couples into the control system with the imperfect knowledge of the
Doppler shift of the light due to relative spacecraft motion along the
LISA arm. This paper outlines requirements on the Doppler shift
knowledge to maintain the cavity well within the resonance when
activating the fused control system. Two Doppler shift estimation
methods are presented that use the already on-board measurements, the
inter-spacecraft interferometer link (the main science measurement), and
the absolute inter-spacecraft laser ranging system. Both methods reach
the required precision after a few thousand seconds of measurement
integration. The paper demonstrates an approach to initialise and engage
the proposed laser stabilization system, starting from free-running
laser and ending with the dual sensor frequency control system. The
results show that the technique lowers the residual laser frequency
noise in the LISA science band by over 3 orders of magnitude,
potentially allowing the requirements on Time-Delay-Interferometry (TDI)
to be relaxed - possibly to the point where first-generation TDI may be
sufficient.
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arXiv:2001.10889 gr-qc
*Observation of a potential future sensitivity limitation from ground
motion at LIGO Hanford *
*Authors*: Jan Harms, Edgard Bonilla, Michael Coughlin, Jenne Driggers,
Sheila Dwyer, David McManus, Michael Ross, Bram Slagmolen, Krishna
Venkateswara
Abstract: A first detection of terrestrial gravity noise in
gravitational-wave detectors is a formidable challenge. With the help of
environmental sensors, it can in principle be achieved before the noise
becomes dominant by estimating correlations between environmental
sensors and the detector. The main complication is to disentangle
different coupling mechanisms between the environment and the detector.
In this paper, we analyze the relations between physical couplings and
correlations that involve ground motion and LIGO strain data h(t)
recorded during its second science run in 2016 and 2017. We find that
all noise correlated with ground motion was more than an order of
magnitude lower than dominant low-frequency instrument noise, and the
dominant coupling over part of the spectrum between ground and h(t) was
residual coupling through the seismic-isolation system. We also present
the most accurate gravitational coupling model so far based on a
detailed analysis of data from a seismic array. Despite our best
efforts, we were not able to unambiguously identify gravitational
coupling in the data, but our improved models confirm previous
predictions that gravitational coupling might already dominate linear
ground-to-h(t) coupling over parts of the low-frequency,
gravitational-wave observation band.
Journal reference: Phys. Rev. D 101, 102002 (2020)
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arXiv:2012.03608 gr-qc astro-ph.IM
*Gravitational-wave physics with Cosmic Explorer: limits to
low-frequency sensitivity *
*Authors*: Evan D. Hall, Kevin Kuns, Joshua R. Smith, Yuntao Bai,
Christopher Wipf, Sebastien Biscans, Rana X Adhikari, Koji Arai, Stefan
Ballmer, Lisa Barsotti, Yanbei Chen, Matthew Evans, Peter Fritschel, Jan
Harms, Brittany Kamai, Jameson Graef Rollins, David Shoemaker, Bram
Slagmolen, Rainer Weiss, Hiro Yamamoto
Abstract: Cosmic Explorer (CE) is a next-generation ground-based
gravitational-wave observatory concept, envisioned to begin operation in
the 2030s, and expected to be capable of observing binary neutron star
and black hole mergers back to the time of the first stars. Cosmic
Explorer's sensitive band will extend below 10 Hz, where the design is
predominantly limited by geophysical, thermal, and quantum noises. In
this work, thermal, seismic, gravity-gradient, quantum, residual gas,
scattered-light, and servo-control noises are analyzed in order to
motivate facility and vacuum system design requirements, potential test
mass suspensions, Newtonian noise reduction strategies, improved
inertial sensors, and cryogenic control requirements. Our analysis shows
that with improved technologies, Cosmic Explorer can deliver a strain
sensitivity better than 10^23 /Hz1/2 down to 5 Hz. Our work refines and
extends previous analysis of the Cosmic Explorer concept and outlines
the key research areas needed to make this observatory a reality.
Journal reference: Phys. Rev. D 103, 122004 (2021)
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arXiv:2109.09882 astro-ph.IM astro-ph.HE gr-qc
*A Horizon Study for Cosmic Explorer: Science, Observatories, and
Community *
*Authors*: Matthew Evans, Rana X Adhikari, Chaitanya Afle, Stefan W.
Ballmer, Sylvia Biscoveanu, Ssohrab Borhanian, Duncan A. Brown, Yanbei
Chen, Robert Eisenstein, Alexandra Gruson, Anuradha Gupta, Evan D. Hall,
Rachael Huxford, Brittany Kamai, Rahul Kashyap, Jeff S. Kissel, Kevin
Kuns, Philippe Landry, Amber Lenon, Geoffrey Lovelace, Lee McCuller, Ken
K. Y. Ng, Alexander H. Nitz, Jocelyn Read, B. S. Sathyaprakash , et al.
(7 additional authors not shown)
Abstract: This Horizon Study describes a next-generation ground-based
gravitational-wave observatory: Cosmic Explorer. With ten times the
sensitivity of Advanced LIGO, Cosmic Explorer will push
gravitational-wave astronomy towards the edge of the observable universe
(z100). The goals of this Horizon Study are to describe and evaluate
design concepts for Cosmic Explorer; to plan for the United States'
leadership in gravitational-wave astronomy; and to envisage the role of
Cosmic Explorer in the international effort to build a
"Third-Generation" (3G) observatory network that will make discoveries
transformative across astronomy, physics, and cosmology.
----------------------------------------------------------------
arXiv:2007.04022 gr-qc
*Spherical orbits around a Kerr black hole *
*Authors*: Edward Teo
Abstract: A special class of orbits known to exist around a Kerr black
hole are spherical orbits -- orbits with constant coordinate radii that
are not necessarily confined to the equatorial plane. Spherical
time-like orbits were first studied by Wilkins almost 50 years ago. In
the present paper, we perform a systematic and thorough study of these
orbits, encompassing and extending previous works on them. We first
present simplified forms for the parameters of these orbits. The
parameter space of these orbits is then analysed in detail; in
particular, we delineate the boundaries between stable and unstable
orbits, bound and unbound orbits, and prograde and retrograde orbits.
Finally, we provide analytic solutions of the geodesic equations, and
illustrate a few representative examples of these orbits.
Journal reference: Gen. Rel. Grav. 53 (2021) 10
----------------------------------------------------------------
arXiv:2004.06984 physics.ins-det astro-ph.IM gr-qc hep-ex
*Broadband Electrical Action Sensing Techniques with conducting wires
for low-mass dark matter axion detection *
*Authors*: Michael Edmund Tobar, Ben T. McAllister, Maxim Goryachev
Abstract: Due to the inverse Primakoff effect it has been shown that
when axions interact with a DC magnetic B-field the resulting electrical
action will produce an AC electromotive force which oscillates at the
Compton frequency of the axion, and may be modeled as an oscillating
effective impressed magnetic current boundary source. We use this result
to calculate the sensitivity of new experiments to low-mass axions using
the quasi-static technique. First, we calculate the current induced in
an electric dipole antenna (straight conducting wire) when the DC
B-field is spatially constant and show that it has a sensitivity
proportional to the axion mass. Following this we extend the topology by
making use of the full extent of the spatially varying DC B-field. This
extension is achieved by transforming the 1D conducting wire to a 2D
winding, to fully link the effective magnetic current boundary source
and thus couple to the full axion induced electrical action. In this
case the conductor becomes a coil winding where the voltage induced
across the winding increases proportionally to the number of windings.
We investigate two different topologies: The 1st uses a single winding,
and couples to the effective short circuit current generated in the
winding, which is read out using a sensitive low impedance SQUID
amplifier: The 2nd uses multiple windings, with every turn effectively
increasing the the voltage output proportional to the winding number.
The read out of this configuration is optimised by implementing a
cryogenic low-noise high input impedance voltage amplifier. The end
result is a new Broadband Electrical Action Sensing Techniques with
orders of magnitude improved sensitivity, which is linearly proportional
to the axion photon coupling and capable of detecting QCD dark matter
axions.
Journal reference: Physics of the Dark Universe 30 (2020) 100624
----------------------------------------------------------------
arXiv:2011.12414 gr-qc astro-ph.CO astro-ph.IM hep-ex hep-ph
*Challenges and Opportunities of Gravitational Wave Searches at MHz to
GHz Frequencies *
*Authors*: N. Aggarwal, O. D. Aguiar, A. Bauswein, G. Cella, S. Clesse,
A. M. Cruise, V. Domcke, D. G. Figueroa, A. Geraci, M. Goryachev, H.
Grote, M. Hindmarsh, F. Muia, N. Mukund, D. Ottaway, M. Peloso, F.
Quevedo, A. Ricciardone, J. Steinlechner, S. Steinlechner, S. Sun, M. E.
Tobar, F. Torrenti, C. Unal, G. White
Abstract: The first direct measurement of gravitational waves by the
LIGO and Virgo collaborations has opened up new avenues to explore our
Universe. This white paper outlines the challenges and gains expected in
gravitational wave searches at frequencies above the LIGO/Virgo band,
with a particular focus on Ultra High-Frequency Gravitational Waves
(UHF-GWs), covering the MHz to GHz range. The absence of known
astrophysical sources in this frequency range provides a unique
opportunity to discover physics beyond the Standard Model operating both
in the early and late Universe, and we highlight some of the most
promising gravitational sources. We review several detector concepts
which have been proposed to take up this challenge, and compare their
expected sensitivity with the signal strength predicted in various
models. This report is the summary of the workshop "Challenges and
opportunities of high-frequency gravitational wave detection" held at
ICTP Trieste, Italy in October 2019, that set up the stage for the
recently launched Ultra-High-Frequency Gravitational Wave (UHF-GW)
initiative.
Journal reference: Living Reviews in Relativity volume 24, Article
number: 4 (2021)
----------------------------------------------------------------
arXiv:2102.05859 gr-qc astro-ph.HE hep-ex physics.ins-det
*Rare Events Detected with a Bulk Acoustic Wave High Frequency
Gravitational Wave Antenna *
*Authors*: Maxim Goryachev, William M. Campbell, Ik Siong Heng, Serge
Galliou, Eugene N. Ivanov, Michael E. Tobar
Abstract: This work describes the operation of a High Frequency
Gravitational Wave detector based on a cryogenic Bulk Acoustic Wave
(BAW) cavity and reports observation of rare events during 153 days of
operation over two seperate experimental runs (Run 1 and Run 2). In both
Run 1 and Run 2 two modes were simultaneously monitored. Across both
runs, the 3rd overtone of the fast shear mode (3B) operating at 5.506
MHz was monitored, while in Run 1 the second mode was chosen to be the
5th OT of the slow shear mode (5C) operating at 8.392 MHz. However, in
Run 2 the second mode was selected to be closer in frequency to the
first mode, and chosen to be the 3rd overtone of the slow shear mode
(3C) operating at 4.993 MHz. Two strong events were observed as
transients responding to energy deposition within acoustic modes of the
cavity. The first event occurred during Run 1 on the 12/05/2019 (UTC),
and was observed in the 5.506 MHz mode, while the second mode at 8.392
MHz observed no event. During Run 2, a second event occurred on the
27/11/2019(UTC) and was observed by both modes. Timing of the events
were checked against available environmental observations as well as
data from other detectors. Various possibilities explaining the origins
of the events are discussed.
Journal reference: Phys. Rev. Lett. 127, 071102 (2021)
----------------------------------------------------------------
arXiv:2109.04056 hep-ph astro-ph.IM gr-qc hep-ex
*Abraham and Minkowski Poynting vector controversy in axion modified
electrodynamics *
*Authors*: Michael E Tobar, Ben T McAllister, Maxim Goryachev
Abstract: The most sensitive haloscopes that search for axion dark
matter through the two photon electromagnetic anomaly, convert axions
into photons through the mixing of axions with a large DC magnetic
field. In this work we apply Poynting theorem to the resulting axion
modified electrodynamics and identify two possible Poynting vectors, one
similar to the Abraham Poynting vector and the other to the Minkowski
Poynting vector in electrodynamics. The latter picks up the extra
non-conservative terms while the former does not. To understand the
source of energy conversion and power flow in the detection systems, we
apply the two Poynting theorems to axion modified electrodynamics, for
both the resonant cavity and broadband low-mass axion detectors. We show
that both Poynting theorems give the same sensitivity for a resonant
cavity axion haloscope, but predict markedly different sensitivity for a
low-mass broadband capacitive haloscope. Hence we ask the question, can
understanding which one is the correct one for axion dark matter
detection, be considered under the framework of the Abraham-Minkowski
controversy? In reality, this should be confirmed by experiment when the
axion is detected. However, many electrodynamic experiments have ruled
in favour of the Minkowski Poynting vector when considering the
canonical momentum in dielectric media. In light of this, we show that
the axion modified Minkowski Poynting vector should indeed be taken
seriously for sensitivity calculation for low-mass axion haloscope
detectors in the quasi static limit, and predict orders of magnitude
better sensitivity than the Abraham Poynting vector equivalent.
----------------------------------------------------------------
arXiv:2009.06517 astro-ph.CO gr-qc hep-ph hep-th
*Screening anisotropy via energy-momentum squared gravity: CDM model
with hidden anisotropy *
*Authors*: Ozgur Akarsu, John D. Barrow, N. Merve Uzun
Abstract: We construct a generalization of the standard CDM model,
wherein we simultaneously replace the spatially flat Robertson-Walker
metric with its simplest anisotropic generalization (LRS Bianchi I
metric), and couple the cold dark matter to the gravity in accordance
with the energy-momentum squared gravity (EMSG) of the form f(T_ T^
)T_ T^ . These two modifications -- namely, two new stiff
fluid-like terms of different nature -- can mutually cancel out, i.e.,
the shear scalar can be screened completely, and reproduce
mathematically exactly the same Friedmann equation of the standard CDM
model. This evades the BBN limits on the anisotropy, and thereby
provides an opportunity to manipulate the cosmic microwave background
quadrupole temperature fluctuation at the desired amount. We further
discuss the consequences of the model on the very early times and far
future of the Universe. This study presents also an example of that the
EMSG of the form f(T_ T^ )T_ T^ , as well as similar type other
constructions, is not necessarily relevant only to very early Universe
but may even be considered in the context of a major problem of the
current cosmology related to the present-day Universe, the so-called H_0
problem.
Journal reference: Phys. Rev. D 102, 124059 (2020)
----------------------------------------------------------------
arXiv:2001.11964 gr-qc astro-ph.CO
*Cosmographic analysis of redshift drift *
*Authors*: Francisco S. N. Lobo, Jose Pedro Mimoso, Matt Visser
Abstract: Redshift drift is the phenomenon whereby the observed redshift
between an emitter and observer comoving with the Hubble flow in an
expanding FLRW universe will slowly evolve --- on a timescale comparable
to the Hubble time. There are nevertheless serious astrometric proposals
for actually observing this effect. We shall however pursue a more
abstract theoretical goal, and perform a general cosmographic analysis
of this effect, eschewing (for now) dynamical considerations in favour
of purely kinematic symmetry considerations based on FLRW spacetimes. We
shall develop various exact results and series expansions for the
redshift drift in terms of the present day Hubble, deceleration, jerk,
snap, crackle, and pop parameters, as well as the present day redshift
of the source. In particular, potential observation of this redshift
drift effect is intimately related to the universe exhibiting a nonzero
deceleration parameter.
Journal reference: JCAP 04 (2020) 043
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arXiv:2002.10659 gr-qc hep-th
*Relativistic combination of non-collinear 3-velocities using quaternions *
*Authors*: Thomas Berry, Matt Visser
Abstract: Quaternions have an (over a century-old) extensive and quite
complicated interaction with special relativity. Since quaternions are
intrinsically 4-dimensional, and do such a good job of handling
3-dimensional rotations, the hope has always been that the use of
quaternions would simplify some of the algebra of the Lorentz
transformations. Herein we report a relatively nice result for the
relativistic combination of non-collinear 3-velocities. If we work with
the relativistic half-velocities w defined by v=2w/(1+w^2 ), and promote
them to quaternions using w=wn^, where n^ is a unit quaternion, then we
shall show
w_1 _ _2= w_1 w_2 =(1w_1 w_2 )^1 (w_1 +w_2 )=(w_1 +w_2 )(1w_2 w_1
)^1.
All of the complicated angular dependence for relativistic combination
of non-collinear 3-velocities is now encoded in the quaternion
multiplication of w1 with w2. This result can furthermore be extended to
obtain an elegant and compact formula for the associated Wigner angle:
e^ =e^^ =(1w_1 w_2 )^1 (1w_2 w_1 ),
in terms of which
n^_1 _ _2 =e^/2 (w1+w_2 )/|w_1 +w_2 |;n^_2 _ _1 =e^/2 (w_1 +w_2
)/|w_1 +w_2 |.
Thus, we would argue, many key results that are ultimately due to the
non-commutativity of non-collinear boosts can be easily rephrased in
terms of the algebra of quaternions.
----------------------------------------------------------------
arXiv:2003.09419 gr-qc
*Dynamic thin-shell black-bounce traversable wormholes *
*Authors*: Francisco S. N. Lobo, Alex Simpson, Matt Visser
Abstract: Based on the recently introduced black-bounce spacetimes, we
shall consider the construction of the related spherically symmetric
thin-shell traversable wormholes within the context of standard general
relativity. All of the really unusual physics is encoded in one simple
parameter a which characterizes the scale of the bounce. Keeping the
discussion as close as possible to standard general relativity is the
theorist's version of only adjusting one feature of the model at a time.
We shall modify the standard thin-shell traversable wormhole
construction, each bulk region now being a black-bounce spacetime, and
with the physics of the thin shell being (as much as possible) derivable
from the Einstein equations. Furthermore, we shall apply a dynamical
analysis to the throat by considering linearized radial perturbations
around static solutions, and demonstrate that the stability of the
wormhole is equivalent to choosing suitable properties for the exotic
material residing on the wormhole throat. The construction is
sufficiently novel to be interesting, and sufficiently straightforward
to be tractable
Journal reference: Phys. Rev. D 101, 124035 (2020)
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arXiv:2005.08533 gr-qc
*Causal hierarchy in modified gravity *
*Authors*: Raul Carballo-Rubio, Francesco Di Filippo, Stefano Liberati,
Matt Visser
Abstract: We investigate the causal hierarchy in various modified
theories of gravity. In general relativity the standard causal
hierarchy, (key elements of which are chronology, causality, strong
causality, stable causality, and global hyperbolicity), is
well-established. In modified theories of gravity there is typically
considerable extra structure, (such as: multiple metrics, aether fields,
modified dispersion relations, Horava-like gravity, parabolic
propagation, etcetera), requiring a reassessment and rephrasing of the
usual causal hierarchy. We shall show that in this extended framework
suitable causal hierarchies can indeed be established, and discuss the
implications for the interplay between "superluminal" propagation and
causality. The key distinguishing feature is whether the signal velocity
is finite or infinite. Preserving even minimal notions of causality in
the presence of infinite signal velocity requires the aether field to be
both unique and hypersurface orthogonal, leading us to introduce the
notion of global parabolicity.
----------------------------------------------------------------
arXiv:2006.14258 gr-qc
*Painleve-Gullstrand form of the Lense-Thirring spacetime *
*Authors*: Joshua Baines, Thomas Berry, Alex Simpson, Matt Visser
Abstract: The standard Lense-Thirring metric is a century-old
slow-rotation large-distance approximation to the gravitational field
outside a rotating massive body, depending only on the total mass and
angular momentum of the source. Although it is not an exact solution to
the vacuum Einstein equations, asymptotically the Lense-Thirring metric
approaches the Kerr metric at large distances. Herein we shall discuss a
specific variant of the standard Lense-Thirring metric, carefully chosen
for simplicity, clarity, and various forms of "improved" behaviour, (to
be more carefully defined in the body of the article). In particular we
shall construct an explicit unit-lapse Painleve-Gullstrand variant of
the Lense-Thirring spacetime, that has flat spatial slices, a very
simple and physically intuitive tetrad, and extremely simple curvature
tensors. We shall verify that this variant of the Lense-Thirring
spacetime is Petrov type I, (so it is not algebraically special), but
nevertheless possesses some very straightforward timelike geodesics,
(the "rain" geodesics). We shall also discuss on-axis and equatorial
geodesics, ISCOs and circular photon orbits. Finally, we wrap up by
discussing some astrophysically relevant estimates, and analyze what
happens if we extrapolate down to small values of r.
----------------------------------------------------------------
arXiv:2008.03817 gr-qc
*Unit-lapse versions of the Kerr spacetime *
*Authors*: Joshua Baines, Thomas Berry, Alex Simpson, Matt Visser
Abstract: The Kerr spacetime is perhaps the most astrophysically
important of the currently known exact solutions to the Einstein field
equations. Whenever spacetimes can be put in unit-lapse form it becomes
possible to identify some very straightforward timelike geodesics, (the
"rain" geodesics), making the physical interpretation of these
spacetimes particularly clean and elegant. The most well-known of these
unit-lapse formulations is the Painleve-Gullstrand form of the
Schwarzschild spacetime, though there is also a Painleve-Gullstrand form
of the Lense-Thirring (slow rotation) spacetime. More radically there
are also two known unit-lapse forms of the Kerr spacetime -- the Doran
and Natario metrics -- though these are not precisely in
Painleve-Gullstrand form. Herein we shall seek to explicate the most
general unit-lapse form of the Kerr spacetime. While at one level this
is "merely" a choice of coordinates, it is a strategically and
tactically useful choice of coordinates, thereby making the technically
challenging but astrophysically crucial Kerr spacetime somewhat easier
to deal with.
----------------------------------------------------------------
arXiv:2008.07046 gr-qc
*Thin-shell traversable wormhole crafted from a regular black hole with
asymptotically Minkowski core *
*Authors*: Thomas Berry, Francisco S. N. Lobo, Alex Simpson, Matt Visser
Abstract: Recently, a novel model for a regular black hole was advocated
which possesses an asymptotically Minkowski core implemented via an
exponential suppression (in the core region) of the Misner-Sharp
quasi-local mass. Using this regular black hole as a template, we shall
construct a spherically symmetric thin-shell traversable wormhole using
the "cut-and-paste" technique, thereby constructing yet another black
hole mimicker. The surface stress-energy at the wormhole throat is
calculated, and the stability of the wormhole is analyzed. An important
result is that, (as compared to their Schwarzschild thin-shell
counterparts), increasing the exponential suppression of the
Misner-Sharp quasi-local mass by increasing the suppression parameter
"a", also considerably increases the stability regions for these
thin-shell wormholes, and furthermore minimizes the amount of energy
condition violating exotic matter required to keep the wormhole throat
open.
Journal reference: Phys. Rev. D 102, 064054 (2020)
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arXiv:2008.13308 gr-qc
*Photon spheres, ISCOs, and OSCOs: Astrophysical observables for regular
black holes with asymptotically Minkowski cores *
*Authors*: Thomas Berry, Alex Simpson, Matt Visser
Abstract: Classical black holes contain a singularity at their core.
This has prompted various researchers to propose a multitude of modified
spacetimes that mimic the physically observable characteristics of
classical black holes as best as possible, but that crucially do not
contain singularities at their cores. Due to recent advances in
near-horizon astronomy, the ability to observationally distinguish
between a classical black hole and a potential black hole mimicker is
becoming increasingly feasible. Herein, we calculate some physically
observable quantities for a recently proposed regular black hole with an
asymptotically Minkowski core -- the radius of the photon sphere and the
extremal stable timelike circular orbit (ESCO). The manner in which the
photon sphere and ESCO relate to the presence (or absence) of horizons
is much more complex than for the Schwarzschild black hole. We find
situations in which photon spheres can approach arbitrarily close to
(near extremal) horizons, situations in which some photon spheres become
stable, and situations in which the locations of both photon spheres and
ESCOs become multi-valued, with both ISCOs (innermost stable circular
orbits) and OSCOs (outermost stable circular orbits). This provides an
extremely rich phenomenology of potential astrophysical interest.
----------------------------------------------------------------
arXiv:2009.01397 gr-qc
*Darboux diagonalization of the spatial 3-metric in Kerr spacetime *
*Authors*: Joshua Baines, Thomas Berry, Alex Simpson, Matt Visser
Abstract: The astrophysical importance of the Kerr spacetime cannot be
overstated. Of the currently known exact solutions to the Einstein field
equations, the Kerr spacetime stands out in terms of its direct
applicability to describing astronomical black hole candidates. In
counterpoint, purely mathematically, there is an old classical result of
differential geometry, due to Darboux, that all 3-manifolds can have
their metrics recast into diagonal form. In the case of the Kerr
spacetime the Boyer-Lindquist coordinates provide an explicit example of
a diagonal spatial 3-metric. Unfortunately, as we demonstrate herein,
Darboux diagonalization of the spatial 3-slices of the Kerr spacetime is
incompatible with simultaneously putting the Kerr metric into unit-lapse
form while retaining manifest axial symmetry. This no-go theorem is
somewhat reminiscent of the no-go theorem to the effect that the spatial
3-slices of the Kerr spacetime cannot be chosen to be conformally flat.
----------------------------------------------------------------
arXiv:2009.12057 gr-qc
*Novel black-bounce spacetimes: wormholes, regularity, energy
conditions, and causal structure *
*Authors*: Francisco S. N. Lobo, Manuel E. Rodrigues, Marcos V. de S.
Silva, Alex Simpson, Matt Visser
Abstract: We develop a number of novel "black-bounce" spacetimes. These
are specific regular black holes where the "area radius" always remains
non-zero, thereby leading to a "throat" that is either timelike
(corresponding to a traversable wormhole), spacelike (corresponding to a
"bounce" into a future universe), or null (corresponding to a "one-way
wormhole"). We shall first perform a general analysis of the regularity
conditions for such a spacetime, and then consider a number of specific
examples. The examples are constructed using a mass function similar to
that of Fan--Wang, and fall into several particular cases, such as the
original Simpson--Visser model, a Bardeen-type model, and other
generalizations thereof. We shall analyse the regularity, the energy
conditions, and the causal structure of these models. The main results
are several new geometries, more complex than before, with two or more
horizons, with the possibility of an extremal case. We shall derive a
general theorem regarding static space-time regularity, and another
general theorem regarding (non)-satisfaction of the classical energy
conditions.
Journal reference: Phys. Rev. D 103, 084052 (2021)
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arXiv:2101.05006 gr-qc
*Inner horizon instability and the unstable cores of regular black holes *
*Authors*: Raúl Carballo-Rubio, Francesco Di Filippo, Stefano Liberati,
Costantino Pacilio, Matt Visser
Abstract: Regular black holes with nonsingular cores have been
considered in several approaches to quantum gravity, and as agnostic
frameworks to address the singularity problem and Hawking's information
paradox. While in a recent work we argued that the inner core is
destabilized by linear perturbations, opposite claims were raised that
regular black holes have in fact stable cores. To reconcile these
arguments, we discuss a generalization of the geometrical framework,
originally applied to Reissner--Nordtsröm black holes by Ori, and show
that regular black holes have an exponentially growing Misner--Sharp
mass at the inner horizon. This result can be taken as an indication
that stable nonsingular black hole spacetimes are not the definitive
endpoint of a quantum gravity regularization mechanism, and that
nonperturbative backreaction effects must be taken into account in order
to provide a consistent description of the quantum-gravitational
endpoint of gravitational stellar collapse.
----------------------------------------------------------------
arXiv:2101.05971 gr-qc math-ph
*Lorentz boosts and Wigner rotations: self-adjoint complexified
quaternions *
*Authors*: Thomas Berry, Matt Visser
Abstract: Herein we shall consider Lorentz boosts and Wigner rotations
from a (complexified) quaternionic point of view. We shall demonstrate
that for a suitably defined self-adjoint complex quaternionic
4-velocity, pure Lorentz boosts can be phrased in terms of the
quaternion square root of the relative 4-velocity connecting the two
inertial frames. Straightforward computations then lead to quite
explicit and relatively simple algebraic formulae for the composition of
4-velocities and the Wigner angle. We subsequently relate the Wigner
rotation to the generic non-associativity of the composition of three
4-velocities, and develop a necessary and sufficient condition for
associativity to hold. Finally, we relate the composition of
4-velocities to a specific implementation of the
Baker-Campbell-Hausdorff theorem. As compared to ordinary 4x4 Lorentz
transformations, the use of self-adjoint complexified quaternions leads,
from a computational view, to storage savings and more rapid
computations, and from a pedagogical view to to relatively simple and
explicit formulae.
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arXiv:2102.01831 gr-qc
*Counterexamples to the maximum force conjecture *
*Authors*: Aden Jowsey, Matt Visser
Abstract: Dimensional analysis shows that the speed of light and
Newton's constant of gravitation can be combined to define a quantity
F_ =c^4 /G_N with the dimensions of force (equivalently, tension). Then
in any physical situation we must have F_physical =fF_ , where the
quantity f is some dimensionless function of dimensionless parameters.
In many physical situations explicit calculation yields f=O(1), and
quite often f1/4. This has lead multiple authors to suggest a (weak or
strong) maximum force/maximum tension conjecture. Working within the
framework of standard general relativity, we will instead focus on
counter-examples to this conjecture, paying particular attention to the
extent to which the counter-examples are physically reasonable. The
various counter-examples we shall explore strongly suggest that one
should not put too much credence into any universal maximum
force/maximum tension conjecture. Specifically, fluid spheres on the
verge of gravitational collapse will generically violate the weak (and
strong) maximum force conjectures. If one wishes to retain any general
notion of "maximum force" then one will have to very carefully specify
precisely which forces are to be allowed within the domain of discourse.
----------------------------------------------------------------
arXiv:2102.02471 gr-qc hep-th
*General class of "quantum deformed" regular black holes *
*Authors*: Thomas Berry, Alex Simpson, Matt Visser
Abstract: We discuss the "quantum deformed Schwarzschild spacetime" as
originally introduced by Kazakov and Solodukhin in 1993, and investigate
the precise sense in which it does and does not satisfy the desiderata
for being a "regular black hole". We shall carefully distinguish (i)
regularity of the metric components, (ii) regularity of the Christoffel
components, and (iii) regularity of the curvature. We shall then embed
the Kazakov-Solodukhin spacetime in a more general framework where these
notions are clearly and cleanly separated. Finally we analyze aspects of
the classical physics of these "quantum deformed Schwarzschild
spacetimes". We shall discuss the surface gravity, the classical energy
conditions, null and timelike geodesics, and the appropriate variant of
Regge--Wheeler equation.
----------------------------------------------------------------
arXiv:2104.11376 gr-qc
*Charged black-bounce spacetimes *
*Authors*: Edgardo Franzin, Stefano Liberati, Jacopo Mazza, Alex
Simpson, Matt Visser
Abstract: Given the recent development of rotating black-bounce-Kerr
spacetimes, for both theoretical and observational purposes it becomes
interesting to see whether it might be possible to construct
black-bounce variants of the entire Kerr-Newman family. Specifically,
herein we shall consider black-bounce-Reissner-Nordström and
black-bounce-Kerr-Newman spacetimes as particularly simple and clean
everywhere-regular black hole "mimickers" that deviate from the
Kerr-Newman family in a precisely controlled and minimal manner, and
smoothly interpolate between regular black holes and traversable
wormholes. While observationally the electric charges on astrophysical
black holes are likely to be extremely low, |Q|/m1, introducing any
non-zero electric charge has a significant theoretical impact. In
particular, we verify the existence of a Killing tensor (and associated
Carter-like constant) but without the full Killing tower of principal
tensor and Killing-Yano tensor, also we discuss how, assuming general
relativity, the black-bounce-Kerr-Newman solution requires an
interesting, non-trivial matter/energy content.
Journal reference: JCAP07(2021)036
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arXiv:2105.03079 gr-qc
*Generic warp drives violate the null energy condition *
*Authors*: Jessica Santiago, Sebastian Schuster, Matt Visser
Abstract: Three very recent articles have claimed that it is possible
to, at least in theory, either set up positive energy warp drives
satisfying the weak energy condition (WEC), or at the very least, to
minimize the WEC violations. These claims are at best incomplete, since
the arguments presented only demonstrate the existence of one set of
timelike observers, the co-moving Eulerian observers, who see "nice"
physics. While these observers might see a positive energy density, the
WEC requires all timelike observers to see positive energy density.
Therefore, one should revisit this issue. A more careful analysis shows
that the situation is actually much grimmer than advertised -- all
physically reasonable warp drives will violate the null energy
condition, and so also automatically violate the WEC, and both the
strong and dominant energy conditions. While warp drives are certainly
interesting examples of speculative physics, the violation of the energy
conditions, at least within the framework of standard general
relativity, is unavoidable. Even in modified gravity, physically
reasonable warp drives will still violate the purely geometrical null
convergence condition and the timelike convergence condition which, in
turn, will place very strong constraints on any modified-gravity warp
drive.
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arXiv:2105.06650 gr-qc
*Reconsidering maximum luminosity *
*Authors*: Aden Jowsey, Matt Visser
Abstract: The suggestion that there is a maximum luminosity (maximum
power) in nature has a long and somewhat convoluted history. Though this
idea is commonly attributed to Freeman Dyson, he was actually much more
circumspect in his views. What is certainly true is that dimensional
analysis shows that the speed of light and Newton's constant of
gravitation can be combined to define a quantity P_* = c^5/G_N with the
dimensions of luminosity (equivalently, power). Then in any physical
situation we must have P_{physical} =P_*, where the quantity is some
dimensionless function of dimensionless parameters. This has lead some
authors to suggest a maximum luminosity/maximum power conjecture.
Working within the framework of standard general relativity, we will
re-assess this conjecture, paying particular attention to the extent to
which various examples and counter-examples are physically reasonable.
We focus specifically on Vaidya spacetimes, and on an evaporating
version of Schwarzschild's constant density star. For both of these
spacetimes luminosity can be arbitrarily large. We argue that any
luminosity bound must depend on delicate internal features of the
radiating object.
----------------------------------------------------------------
arXiv:2106.05002 gr-qc
*Tractor beams, pressor beams, and stressor beams in general relativity *
*Authors*: Jessica Santiago, Sebastian Schuster, Matt Visser
Abstract: The metrics of general relativity generally fall into two
categories: Those which are solutions of the Einstein equations for a
given source energy-momentum tensor, and the "reverse engineered"
metrics -- metrics bespoke for a certain purpose. Their energy-momentum
tensors are then calculated by inserting these into the Einstein
equations. This latter approach has found frequent use when confronted
with creative input from fiction, wormholes and warp drives being the
most famous examples. In this paper, we shall again take inspiration
from fiction, and see what general relativity can tell us about the
possibility of a gravitationally induced tractor beam. We will base our
construction on warp drives and show how versatile this ansatz alone
proves to be. Not only can we easily find tractor beams (attracting
objects); repulsor/pressor beams are just as attainable, and a
generalization to "stressor" beams is seen to present itself quite
naturally. We show that all of these metrics would violate various
energy conditions. This will provide an opportunity to ruminate on the
meaning of energy conditions as such, and what we can learn about
whether an arbitrarily advanced civilization might have access to such
beams.
----------------------------------------------------------------
arXiv:2107.00343 math-ph gr-qc
*Explicit Baker-Campbell-Hausdorff-Dynkin formula for Spacetime via
Geometric Algebra *
*Authors*: Joseph Wilson, Matt Visser
Abstract: We present a compact Baker-Campbell-Hausdorff-Dynkin formula
for the composition of Lorentz transformations ei in the spin
representation (a.k.a. Lorentz rotors) in terms of their generators _i :
ln(e^1 e^2 )=tanh^1 (tanh1+tanh_2 +(1/2)[tanh_1 ,tanh_2
]1+(1/2){tanh_1 ,tanh_2 })
This formula is general to geometric algebras (a.k.a. real Clifford
algebras) of dimension 4, naturally generalising Rodrigues' formula for
rotations in R^3 . In particular, it applies to Lorentz rotors within
the framework of Hestenes' spacetime algebra, and provides an efficient
method for composing Lorentz generators. Computer implementations are
possible with a complex 2×2 matrix representation realised by the Pauli
spin matrices. The formula is applied to the composition of relativistic
3-velocities yielding simple expressions for the resulting boost and the
concomitant Wigner angle.
----------------------------------------------------------------
arXiv:2110.01814 gr-qc
*Killing tensor and Carter constant for Painleve-Gullstrand form of
Lense-Thirring spacetime *
*Authors*: Joshua Baines, Thomas Berry, Alex Simpson, Matt Visser
Abstract: Recently, the authors have formulated and explored a novel
Painleve-Gullstrand variant of the Lense-Thirring spacetime, which has
some particularly elegant features -- including unit-lapse,
intrinsically flat spatial 3-slices, and some particularly simple
geodesics, the "rain" geodesics. At linear level in the rotation
parameter this spacetime is indistinguishable from the usual
slow-rotation expansion of Kerr. Herein, we shall show that this
spacetime possesses a nontrivial Killing tensor, implying separability
of the Hamilton-Jacobi equation. Furthermore, we shall show that the
Klein-Gordon equation is also separable on this spacetime. However,
while the Killing tensor has a 2-form square root, we shall see that
this 2-form square root of the Killing tensor is not a Killing-Yano
tensor. Finally, the Killing-tensor-induced Carter constant is easily
extracted, and now, with a fourth constant of motion, the geodesics
become (in principle) explicitly integrable.
Journal reference: Universe 7 (2021) 473
----------------------------------------------------------------
arXiv:2110.14926 gr-qc
*Tractor beams, pressor beams, and stressor beams within the context of
general relativity *
*Authors*: Matt Visser, Jessica Santiago, Sebastian Schuster
Abstract: Both traversable wormholes and warp drives, concepts
originally developed within the context of science fiction, have now
(for some 30 odd years) been studied, debated, and carefully analyzed
within the framework of general relativity. An overarching theme of the
general relativistic analysis is unavoidable violations of the classical
point-wise energy conditions. Another science fiction trope, now over 80
years old, is the tractor beam and/or pressor beam. We shall discuss how
to formulate both tractor beams and/or pressor beams, and a variant to
be called a stressor beam, within the context of reverse engineering the
spacetime metric. (While such reverse engineering is certainly well
beyond our civilization's current capabilities, we shall be more
interested in asking what an arbitrarily advanced civilization might be
able to accomplish.) We shall see that tractor beams and/or pressor
beams can be formulated by suitably modifying the notion of warp drives,
and that, as for wormholes and warp drives, violations of the classical
point-wise energy conditions are utterly unavoidable.
----------------------------------------------------------------
arXiv:2111.03113 gr-qc hep-th
*Geodesically complete black holes in Lorentz-violating gravity *
*Authors*: Raúl Carballo-Rubio, Francesco Di Filippo, Stefano Liberati,
Matt Visser
Abstract: We present a systematic study of the geometric structure of
non-singular spacetimes describing black holes in Lorentz-violating
gravity. We start with a review of the definition of trapping horizons,
and the associated notions of trapped and marginally trapped surfaces,
and then study their significance in frameworks with modified dispersion
relations. This leads us to introduce the notion of universally
marginally trapped surfaces, as the direct generalization of marginally
trapped surfaces for frameworks with infinite signal velocities
(Hoava-like frameworks), which then allows us to define universal
trapping horizons. We find that trapped surfaces cannot be generalized
in the same way, and discuss in detail why this does not prevent using
universal trapping horizons to define black holes in Hoava-like
frameworks. We then explore the interplay between the kinematical part
of Penrose's singularity theorem, which implies the existence of
incomplete null geodesics in the presence of a focusing point, and the
existence of multiple different metrics. This allows us to present a
complete classification of all possible geometries that neither display
incomplete physical trajectories nor curvature singularities. Our main
result is that not all classes that exist in frameworks in which all
signal velocities are realized in Hoava-like frameworks. However, the
taxonomy of geodesically complete black holes in Ho\v rava-like
frameworks includes diverse scenarios such as evaporating regular black
holes, regular black holes bouncing into regular white holes, and hidden
wormholes.
----------------------------------------------------------------
arXiv:2111.12329 gr-qc
*The eye of the storm: A regular Kerr black hole *
*Authors*: Alex Simpson, Matt Visser
Abstract: We present a highly tractable non-singular modification of the
Kerr geometry, dubbed the "eye of the storm" -- a rotating regular black
hole with an asymptotically Minkowski core. This is achieved by
"exponentially suppressing" the mass parameter in the Kerr spacetime:
mme^/r . The single parameter quantifies the deviation from the
usual Kerr spacetime. Some of the classical energy conditions are
globally satisfied, whilst certain choices for force any
energy-condition-violating physics into the deep core. The geometry
possesses the full "Killing tower'" of principal tensor, Killing--Yano
tensor, and nontrivial Killing tensor, with associated Carter constant;
hence the Hamilton--Jacobi equations are separable, and the geodesics
integrable. The Klein--Gordon equation is also separable on this
candidate spacetime. The tightly controlled deviation from Kerr renders
the physics extraordinarily tractable when compared with analogous
results in the current literature. This spacetime will be amenable to
straightforward extraction of astrophysical observables falsifiable/
verifiable by the experimental community.
----------------------------------------------------------------
arXiv:2111.14016 gr-qc hep-th
*Feynman's i-epsilon prescription, almost real spacetimes, and
acceptable complex spacetimes *
*Authors*: Matt Visser
Abstract: Feynman's i-epsilon prescription for quantum field theoretic
propagators has a quite natural reinterpretation in terms of a slight
complex deformation of the Minkowski spacetime metric. Though originally
a strictly flat-space result, once reinterpreted in this way, these
ideas can be naturally extended first to semi-classical curved-spacetime
QFT on a fixed background geometry and then, (with more work), to
fluctuating spacetime geometries. There are intimate connections with
variants of the weak energy condition. We shall take the Lorentzian
signature metric as primary, but note that allowing the complex
deformation to become large leads to a variant of Wick rotation, and
more importantly leads to physically motivated constraints on the
configuration space of acceptable off-shell geometries to include in
Feynman's functional integral when attempting to quantize gravity.
Ultimately this observation allows one to connect the discussion back to
recent ideas on "acceptable" complex metrics, in the Louko-Sorkin and
Kontsevich-Segal-Witten sense, with Lorentzian signature spacetimes
occurring exactly on the boundary of the set of "acceptable" complex
metrics. By adopting the tetrad formalism we explicitly construct the
most general set of acceptable complex metrics satisfying the 0-form,
1-form, and 2-form acceptability conditions.
----------------------------------------------------------------
arXiv:2005.04027 gr-qc cond-mat.other quant-ph
*The next generation of analogue gravity experiments *
*Authors*: Maxime J Jacquet, Silke Weinfurtner, Friedrich Koenig
Abstract: This article is an introduction for a theme issue following a
Scientific Discussion Meeting on \emph{The next generation of analogue
gravity experiments} held at the Royal Society in December 2019. This
theme issue comprises a collection of recent advances of the research
programme, as well as their philosophical implications, that were
presented at the meeting.
----------------------------------------------------------------
arXiv:1802.09807
gr-qc
*Boyer-Lindquist space-times and beyond: Meta-material analogues *
* *
*Authors:* Sebastian Schuster
, Matt Visser
Abstract: Physically reasonable stationary axisymmetric spacetimes can
(under very mild technical conditions) be put into Boyer-Lindquist form.
Unfortunately a metric presented in Boyer-Lindquist form is not
well-adapted to the "quasi-Cartesian" meta-material analysis we
developed in our previous article on "bespoke analogue spacetimes"
(arXiv:1801.05549 [gr-qc]). In the current article we first focus
specifically on spacetime metrics presented in Boyer-Lindquist form, and
determine the equivalent meta-material susceptibility tensors in a
laboratory setting. We then turn to analyzing generic stationary
spacetimes, again determining the equivalent meta-material
susceptibility tensors. While the background laboratory metric is always
taken to be Riemann-flat, we now allow for arbitrary curvilinear
coordinate systems. Finally, we reconsider static spherically symmetric
spacetimes, but now in general spherical polar rather than
quasi-Cartesian coordinates. The article provides a set of general tools
for mimicking various interesting spacetimes by using non-trivial
susceptibility tensors in general laboratory settings.
----------------------------------------------------------------
arXiv:2007.03769 gr-qc physics.flu-dyn
*Superradiance in dispersive black hole analogues *
*Authors*: Sam Patrick, Silke Weinfurtner
Abstract: Wave equations containing spatial derivatives which are higher
than second order arise naturally in the context of condensed matter
systems. The solutions of such equations contain more than two modes and
consequently, the range of possible interactions between the different
modes is significantly enhanced compared to the two mode case. We
develop a framework for analysing the different mode interactions based
on the classical turning points of the dispersion relation. We then
apply this framework to the scattering of deep water gravity waves with
a draining bathtub vortex, a system which constitutes the analogue of a
rotating black hole in the non-dispersive limit. In particular, we show
that the different scattering outcomes are controlled by the light-ring
frequencies, a concept routinely applied in black hole physics, and two
new frequencies which are related to the strength of dispersion. We find
that the frequency range in which the reflected wave is superradiantly
amplified appears as a simple modification to the non-dispersive case.
However, the condition to observe this amplification is complicated by
the fact that a superradiant mode can be reflected back into the system
by scattering with one of the additional modes. We provide estimates for
the reflection coefficients in the full dispersive regime.
Journal reference: Phys. Rev. D 102, 084041 (2020)
----------------------------------------------------------------
arXiv:2007.07160 gr-qc cond-mat.quant-gas
*Interferometric Unruh detectors for Bose-Einstein condensates *
*Authors*: Cisco Gooding, Steffen Biermann, Sebastian Erne, Jorma Louko,
William G. Unruh, Joerg Schmiedmayer, Silke Weinfurtner
Abstract: The Unruh effect predicts a thermal response for an
accelerated detector moving through the vacuum. Here we propose an
interferometric scheme to observe an analogue of the circular Unruh
effect using a localized laser coupled to a Bose-Einstein condensate
(BEC). Quantum fluctuations in the condensate are governed by an
effective relativistic field theory, and as demonstrated, the coupled
laser field acts as an effective Unruh-DeWitt detector thereof. The
effective speed of light is lowered by 12 orders of magnitude to the
sound velocity in the BEC. For detectors traveling close to the sound
speed, observation of the Unruh effect in the analogue system becomes
experimentally feasible.
Journal reference: Phys. Rev. Lett. 125, 213603 (2020)
----------------------------------------------------------------
arXiv:2007.09523 gr-qc cond-mat.quant-gas
*Unruh and analogue Unruh temperatures for circular motion in 3+1 and
2+1 dimensions *
*Authors*: Steffen Biermann, Sebastian Erne, Cisco Gooding, Jorma Louko,
Jörg Schmiedmayer, William G. Unruh, Silke Weinfurtner
Abstract: The Unruh effect states that a uniformly linearly accelerated
observer with proper acceleration a experiences Minkowski vacuum as a
thermal state in the temperature T_lin =a/(2), operationally measurable
via the detailed balance condition between excitation and de-excitation
probabilities. An observer in uniform circular motion experiences a
similar Unruh-type temperature Tcirc, operationally measurable via the
detailed balance condition, but T_circ depends not just on the proper
acceleration but also on the orbital radius and on the excitation
energy. We establish analytic results for T_circ for a massless scalar
field in 3+1 and 2+1 spacetime dimensions in several asymptotic regions
of the parameter space, and we give numerical results in the
interpolating regions. In the ultrarelativistic limit, we verify that in
3+1 dimensions T_circ is of the order of T_lin uniformly in the energy,
as previously found by Unruh, but in 2+1 dimensions T_circ is
significantly lower at low energies. We translate these results to an
analogue spacetime nonrelativistic field theory in which the circular
acceleration effects may become experimentally testable in the near
future. We establish in particular that the circular motion analogue
Unruh temperature grows arbitrarily large in the near-sonic limit,
encouragingly for the experimental prospects, but the growth is weaker
in effective spacetime dimension 2+1 than in 3+1.
Journal reference: Phys. Rev. D 102, 085006 (2020)
----------------------------------------------------------------
arXiv:2105.11509 gr-qc cond-mat.quant-gas physics.flu-dyn
*The sound-ring radiation of expanding vortex clusters *
*Authors*: August Geelmuyden, Sebastian Erne, Sam Patrick, Carlo
Barenghi, Silke Weinfurtner
Abstract: We investigate wave-vortex interaction emerging from an
expanding compact vortex cluster in a two-dimensional Bose-Einstein
condensate. We adapt techniques developed for compact gravitational
objects to derive the characteristic modes of the wave-vortex
interaction perturbatively around an effective vortex flow field. We
demonstrate the existence of orbits or sound-rings, in analogy to
gravitational light-rings, and compute the characteristic spectrum for
the out-of-equilibrium vortex cluster. The spectrum obtained from
numerical simulations of a stochastic Gross-Pitaevskii equation
exhibiting an expanding vortex cluster is in excellent agreement with
analytical predictions. Our findings are relevant for 2d-quantum
turbulence, the semi-classical limit around fluid flows, and rotating
compact objects exhibiting discrete circulation.
----------------------------------------------------------------
arXiv:2011.06787 gr-qc
*The SPIIR online coherent pipeline to search for gravitational waves
from compact binary coalescences *
*Authors*: Qi Chu, Manoj Kovalam, Linqing Wen, Teresa Slaven-Blair, Joel
Bosveld, Yanbei Chen, Patrick Clearwater, Alex Codoreanu, Zhihui Du,
Xiangyu Guo, Xiaoyang Guo, Kyungmin Kim, Tjonnie G. F. Li, Victor
Oloworaran, Fiona Panther, Jade Powell, Anand S. Sengupta, Karl Wette,
Xingjiang Zhu
Abstract: This paper presents the SPIIR pipeline used for public alerts
during the third advanced LIGO and Virgo observation run (O3 run). The
SPIIR pipeline uses infinite impulse response (IIR) filters to perform
extremely low-latency matched filtering and this process is further
accelerated with graphics processing units (GPUs). It is the first
online pipeline to select candidates from multiple detectors using a
coherent statistic based on the maximum network likelihood ratio
statistic principle. Here we simplify the derivation of this statistic
using the singular-value-decomposition (SVD) technique and show that
single-detector signal-to-noise ratios from matched filtering can be
directly used to construct the statistic for each sky direction.
Coherent searches are in general more computationally challenging than
coincidence searches due to extra search over sky direction parameters.
The search over sky directions follows an embarrassing parallelization
paradigm and has been accelerated using GPUs. The detection performance
is reported using a segment of public data from LIGO-Virgo's second
observation run. We demonstrate that the median latency of the SPIIR
pipeline is less than 9 seconds, and present an achievable roadmap to
reduce the latency to less than 5 seconds. During the O3 online run,
SPIIR registered triggers associated with 38 of the 56 non-retracted
public alerts. The extreme low-latency nature makes it a competitive
choice for joint time-domain observations, and offers the tantalizing
possibility of making public alerts prior to the merger phase of binary
coalescence systems involving at least one neutron star.
----------------------------------------------------------------
arXiv:2012.09552 stro-ph.IM gr-qc
*SWIGLAL: Python and Octave interfaces to the LALSuite
gravitational-wave data analysis libraries *
*Authors*: Karl Wette
Abstract: The LALSuite data analysis libraries, written in C, implement
key routines critical to the successful detection of gravitational
waves, such as the template waveforms describing the merger of two black
holes or two neutron stars. SWIGLAL is a component of LALSuite which
provides interfaces for Python and Octave, making LALSuite routines
accessible directly from scripts written in those languages. It has
enabled modern gravitational-wave data analysis software, used in the
first detection of gravitational waves, to be written in Python, thereby
benefiting from its ease of development and rich feature set, while
still having access to the computational speed and scientific
trustworthiness of the routines provided by LALSuite.
Journal reference: SoftwareX 12 (2020) 100634
----------------------------------------------------------------
arXiv:2104.14829 gr-qc astro-ph.IM
*Geometric Approach to Analytic Marginalisation of the Likelihood Ratio
for Continuous Gravitational Wave Searches *
*Authors*: Karl Wette
Abstract: The likelihood ratio for a continuous gravitational wave
signal is viewed geometrically as a function of the orientation of two
vectors; one representing the optimal signal-to-noise ratio, the other
representing the maximised likelihood ratio or F-statistic. Analytic
marginalisation over the angle between the vectors yields a marginalised
likelihood ratio which is a function of the F-statistic. Further
analytic marginalisation over the optimal signal-to-noise ratio is
explored using different choices of prior. Monte-Carlo simulations show
that the marginalised likelihood ratios have identical detection power
to the F-statistic. This approach demonstrates a route to viewing the
F-statistic in a Bayesian context, while retaining the advantages of its
efficient computation.
Journal reference: Universe 2021, 7(6), 174
----------------------------------------------------------------
arXiv:2106.16142 gr-qc astro-ph.HE
*Template Lattices for a Cross-Correlation Search for Gravitational
Waves from Scorpius X-1 *
*Authors*: Katelyn J. Wagner, John T. Whelan, Jared K. Wofford, Karl Wette
Abstract: We describe the application of the lattice covering problem to
the placement of templates in a search for continuous gravitational
waves from the low-mass X-Ray binary Scorpius X-1. Efficient placement
of templates to cover the parameter space at a given maximum mismatch is
an application of the sphere covering problem, for which an
implementation is available in the LatticeTiling software library. In
the case of Sco X-1, potential correlations, in both the prior
uncertainty and the mismatch metric, between the orbital period and
orbital phase, lead to complications in the efficient construction of
the lattice. We define a shearing coordinate transformation which
simultaneously minimizes both of these sources of correlation, and
allows us to take advantage of the small prior orbital period
uncertainty. The resulting lattices have a factor of about 3 fewer
templates than the corresponding parameter space grids constructed by
the prior straightforward method, allowing a more sensitive search at
the same computing cost and maximum mismatch.
----------------------------------------------------------------
arXiv:1912.08988 gr-qc hep-th
*Positive Energy Functional for Massless Scalars in Rotating Black Hole
Backgrounds of Maximal Ungauged Supergravity *
*Authors*: M. Cvetic, G. W. Gibbons, C. N. Pope, B. F. Whiting
Abstract: We outline a proof of the stability of a massless neutral
scalar field in the background of a wide class of four dimensional
asymptotically flat rotating and ``electrically charged'' solutions of
supergravity, and the low energy limit of string theory, known as STU
metrics. Despite their complexity, we find it possible to circumvent the
difficulties presented by the existence of ergo-regions and the related
phenomenon of super-radiance in the original metrics by following a
strategy due to Whiting, and passing to an auxiliary metric admitting an
everywhere lightlike Killing field and constructing a scalar field
(related to a possible unstable mode by a non-local transformation)
which satisfies the massless wave equation with respect to the auxiliary
metric. By contrast with the case for , the associated energy density
of is not only conserved but is also non-negative.
Journal reference: Phys. Rev. Lett. 124, 231102 (2020)
----------------------------------------------------------------
arXiv:2002.02501 gr-qc quant-ph
*Classical Tools for Antipodal Identification in Reissner-Nordström
Spacetime *
*Authors*: Nathaniel A. Strauss, Bernard F. Whiting, Anne T. Franzen
Abstract: We extend the discussion of the antipodal identification of
black holes to the Reissner-Nordström (RN) spacetime by developing the
classical tools necessary to define the corresponding quantum field
theory (QFT). We solve the massless Klein-Gordon equation in the RN
background in terms of scattering coefficients and provide a procedure
for constructing a solution for an arbitrary analytic extension of RN.
The behavior of the maximally extended solution is highly dependent upon
the coefficients of scattering between the inner and outer horizons, so
we present the low-frequency behavior of, and numerical solutions for,
these quantities. We find that, for low enough frequency, field
amplitudes of solutions with purely positive or negative frequency at
each horizon will acquire only a phase after passing both the inner and
outer horizons, while at higher frequencies the amplitudes will tend to
grow exponentially either to the future or to the past, and decay
exponentially in the other direction. Regardless, we can always
construct a basis of globally antipodal symmetric and antisymmetric
solutions for any finite analytic extension of RN. We have characterized
this basis in terms of positive and negative frequency solutions for
future use in constructing the corresponding QFT.
Journal reference: Class. Quant. Grav. 37 (2020) 18, 185006
----------------------------------------------------------------
arXiv:2101.00856 gr-qc math-ph
*On the geometry of Petrov type II spacetimes *
*Authors*: Steffen Aksteiner, Lars Andersson, Bernardo Araneda, Bernard
Whiting
Abstract: In general, geometries of Petrov type II do not admit
symmetries in terms of Killing vectors or spinors. We introduce a weaker
form of Killing equations which do admit solutions. In particular, there
is an analog of the Penrose-Walker Killing spinor. Some of its
properties, including associated conservation laws, are discussed.
Perturbations of Petrov type II Einstein geometries in terms of a
complex scalar Debye potential yield complex solutions to the linearized
Einstein equations. The complex linearized Weyl tensor is shown to be
half Petrov type N. The remaining curvature component on the
algebraically special side is reduced to a first order differential
operator acting on the potential.
----------------------------------------------------------------
arXiv:2106.05163 gr-qc
*The First-Order Velocity Memory Effect from Compact Binary Coalescing
Sources *
*Authors*: Atul K. Divakarla, Bernard F. Whiting
Abstract: It has long been known that gravitational waves from compact
binary coalescing sources are responsible for a first-order displacement
memory effect experienced by a pair of freely falling test masses. This
constant displacement is sourced from the non-vanishing final
gravitational-wave strain present in the wave's after-zone, often
referred to as the non-linear memory effect, and is of the same order of
magnitude as the strain from the outgoing quadrupole radiation. Hence,
this prediction of general relativity is verifiable experimentally by
measurement of the final relative separation between test masses that
comprise gravitational-wave detectors. In a separate context,
independent calculations have demonstrated that exact, sandwich, plane
wave spacetimes exhibit a velocity memory effect: a non-zero relative
velocity, gained by a pair of test masses in free fall, after the
passage of a gravitational wave. In this paper, we find that in addition
to the known constant displacement memory effect test masses experience,
a velocity memory effect at leading order arises due to the non-linear
nature of gravitational waves from compact binary sources. We discuss
the magnitude of the first-order velocity memory effect in the context
of observing gravitational-wave radiation from super massive binary
black hole mergers in LISA.
Journal reference: Phys. Rev. D 104, 064001 (2021)
----------------------------------------------------------------
arXiv:2109.03254 gr-qc hep-th
Supergravity Black Holes, Love Numbers and Harmonic Coordinates
Authors: M. Cvetic, G. W. Gibbons, C. N. Pope, B. F. Whiting
Abstract: To perform realistic tests of theories of gravity, we need to
be able to look beyond general relativity and evaluate the consistency
of alternative theories with observational data from, especially,
gravitational wave detections using, for example, an agnostic Bayesian
approach. In this paper we further examine properties of one class of
such viable, alternative theories, based on metrics arising from
ungauged supergravity. In particular, we examine the massless, neutral,
minimally coupled scalar wave equation in a general stationary,
axisymmetric background metric such as that of a charged rotating black
hole, when the scalar field is either time independent or in the
low-frequency, near-zone limit, with a view to calculating the Love
numbers of tidal perturbations, and of obtaining harmonic coordinates
for the background metric. For a four-parameter family of charged
asymptotically flat rotating black hole solutions of ungauged
supergravity theory known as STU black holes, which includes
Kaluza-Klein black holes and the Kerr-Sen black hole as special cases,
we find that all time-independent solutions, and hence the harmonic
coordinates of the metrics, are identical to those of the Kerr solution.
In the low-frequency limit we find the scalar fields exhibit the same
SL(2,R) symmetry as holds in the case of the Kerr solution. We point out
extensions of our results to a wider class of metrics, which includes
solutions of Einstein-Maxwell-Dilaton theory.
******************************************************************************
ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc,
December 2019 - November 2021
The LIGO Scientific Collaboration is a consortium of scientific
institutions doing work on the Laser Interferometer Gravitational-Wave
Observatory (LIGO), which consists of two laser interferometers 3030 km
apart, one at Hanford, Washington State and the other at Livingston,
Louisiana. The LIGO Scientific Collaboration includes ASGRG members
David Blair, Philip Charlton, Neil Cornish, Brynmor Haskell, Jörg
Hennig, Paul Lasky, Ju Li, David McClelland, Andrew Melatos, Susan
Scott, Daniel Shaddock, Bram Slagmolen, Peter Veitch, Karl Wette,
Bernard Whiting and Chunnong Zhao.
Listed below are all the abstracts listed on gr-qc from December 2019 to
November 2021 from consortia that include at leastone ASGRG member as a
co-author these are mostly LIGO abstracts, but there are occasionally
some from eLISA and Virgo.
----------------------------------------------------------------
arXiv:1912.11716 gr-qc astro-ph.IM
*Open data from the first and second observing runs of Advanced LIGO and
Advanced Virgo *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration.
Abstract: Advanced LIGO and Advanced Virgo are actively monitoring the
sky and collecting gravitational-wave strain data with sufficient
sensitivity to detect signals routinely. In this paper we describe the
data recorded by these instruments during their first and second
observing runs. The main data products are the gravitational-wave strain
arrays, released as time series sampled at 16384 Hz. The datasets that
include this strain measurement can be freely accessed through the
Gravitational Wave Open Science Center at http://gw-openscience.org,
together with data-quality information essential for the analysis of
LIGO and Virgo data, documentation, tutorials, and supporting software.
Journal reference: SoftwareX 13 (2021) 100658
----------------------------------------------------------------
arXiv:2001.01761 astro-ph.HE gr-qc
*GW190425: Observation of a Compact Binary Coalescence with Total Mass
****3.4M**** *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration.
Abstract: On 2019 April 25, the LIGO Livingston detector observed a
compact binary coalescence with signal-to-noise ratio 12.9. The Virgo
detector was also taking data that did not contribute to detection due
to a low signal-to-noise ratio, but were used for subsequent parameter
estimation. The 90% credible intervals for the component masses range
from 1.12 to 2.52 M(1.45 to 1.88 Mif we restrict the dimensionless
component spin magnitudes to be smaller than 0.05). These mass
parameters are consistent with the individual binary components being
neutron stars. However, both the source-frame chirp mass 1.44^+0.02
_0.02 Mand the total mass 3.4^+0.3 _0.1 Mof this system are
significantly larger than those of any other known binary neutron star
system. The possibility that one or both binary components of the system
are black holes cannot be ruled out from gravitational-wave data. We
discuss possible origins of the system based on its inconsistency with
the known Galactic binary neutron star population. Under the assumption
that the signal was produced by a binary neutron star coalescence, the
local rate of neutron star mergers is updated to 2502810Gpc^3 yr^1 .
Journal reference: Astrophysical Journal Letters 892 (2020) L3
----------------------------------------------------------------
arXiv:2001.00923 astro-ph.HE
*A Joint Fermi-GBM and LIGO/Virgo Analysis of Compact Binary Mergers
From the First and Second Gravitational-wave Observing Runs *
*Authors*: The Fermi Gamma-ray Burst Monitor Team, the LIGO Scientific
Collaboration, the Virgo Collaboration.
Abstract: We present results from offline searches of Fermi Gamma-ray
Burst Monitor (GBM) data for gamma-ray transients coincident with the
compact binary coalescences observed by the gravitational-wave (GW)
detectors Advanced LIGO and Advanced Virgo during their first and second
observing runs. In particular, we perform follow-up for both confirmed
events and low significance candidates reported in the LIGO/Virgo
catalog GWTC-1. We search for temporal coincidences between these GW
signals and GBM triggered gamma-ray bursts (GRBs). We also use the GBM
Untargeted and Targeted subthreshold searches to find coincident
gamma-rays below the on-board triggering threshold. This work implements
a refined statistical approach by incorporating GW astrophysical source
probabilities and GBM visibilities of LIGO/Virgo sky localizations to
search for cumulative signatures of coincident subthreshold gamma-rays.
All search methods recover the short gamma-ray burst GRB 170817A
occurring ~1.7 s after the binary neutron star merger GW170817. We also
present results from a new search seeking GBM counterparts to LIGO
single-interferometer triggers. This search finds a candidate joint
event, but given the nature of the GBM signal and localization, as well
as the high joint false alarm rate of 1.1×10^6 Hz, we do not consider
it an astrophysical association. We find no additional coincidences.
Journal reference: The Astrophysical Journal, 893:100 (14pp), 2020 April 20
----------------------------------------------------------------
arXiv:2004.08342 astro-ph.HE gr-qc
*GW190412: Observation of a Binary-Black-Hole Coalescence with
Asymmetric Masses *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration.
Abstract: We report the observation of gravitational waves from a
binary-black-hole coalescence during the first two weeks of LIGO's and
Virgo's third observing run. The signal was recorded on April 12, 2019
at 05:30:44 UTC with a network signal-to-noise ratio of 19. The binary
is different from observations during the first two observing runs most
notably due to its asymmetric masses: a ~30 solar mass black hole merged
with a ~8 solar mass black hole companion. The more massive black hole
rotated with a dimensionless spin magnitude between 0.22 and 0.60 (90%
probability). Asymmetric systems are predicted to emit gravitational
waves with stronger contributions from higher multipoles, and indeed we
find strong evidence for gravitational radiation beyond the leading
quadrupolar order in the observed signal. A suite of tests performed on
GW190412 indicates consistency with Einstein's general theory of
relativity. While the mass ratio of this system differs from all
previous detections, we show that it is consistent with the population
model of stellar binary black holes inferred from the first two
observing runs.
Journal reference: Phys. Rev. D 102, 043015 (2020)
----------------------------------------------------------------
arXiv:2006.00714 astro-ph.IM gr-qc
*Bayesian inference for compact binary coalescences with BILBY:
Validation and application to the first LIGO--Virgo gravitational-wave
transient catalogue *
*Authors*: I. M. Romero-Shaw, C. Talbot, S. Biscoveanu, V. D'Emilio, G.
Ashton, C. P. L. Berry, S. Coughlin, S. Galaudage, C. Hoy, M. Huebner,
K. S. Phukon, M. Pitkin, M. Rizzo, N. Sarin, R. Smith, S. Stevenson, A.
Vajpeyi, M. Arene, K. Athar, S. Banagiri, N. Bose, M. Carney, K.
Chatziioannou, J. A. Clark, M. Colleoni , et al. (34 additional authors
not shown)
Abstract: Gravitational waves provide a unique tool for observational
astronomy. While the first LIGO--Virgo catalogue of gravitational-wave
transients (GWTC-1) contains eleven signals from black hole and neutron
star binaries, the number of observations is increasing rapidly as
detector sensitivity improves. To extract information from the observed
signals, it is imperative to have fast, flexible, and scalable inference
techniques. In a previous paper, we introduced BILBY: a modular and
user-friendly Bayesian inference library adapted to address the needs of
gravitational-wave inference. In this work, we demonstrate that BILBY
produces reliable results for simulated gravitational-wave signals from
compact binary mergers, and verify that it accurately reproduces results
reported for the eleven GWTC-1 signals. Additionally, we provide
configuration and output files for all analyses to allow for easy
reproduction, modification, and future use. This work establishes that
BILBY is primed and ready to analyse the rapidly growing population of
compact binary coalescence gravitational-wave signals.
----------------------------------------------------------------
arXiv:2006.12611 astro-ph.HE gr-qc
*GW190814: Gravitational Waves from the Coalescence of a 23 M****Black
Hole with a 2.6 M****Compact Object *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration.
Abstract: We report the observation of a compact binary coalescence
involving a 22.2 - 24.3 Mblack hole and a compact object with a mass of
2.50 - 2.67 M(all measurements quoted at the 90% credible level). The
gravitational-wave signal, GW190814, was observed during LIGO's and
Virgo's third observing run on August 14, 2019 at 21:10:39 UTC and has a
signal-to-noise ratio of 25 in the three-detector network. The source
was localized to 18.5 deg^2 at a distance of 241^+41 _45 Mpc; no
electromagnetic counterpart has been confirmed to date. The source has
the most unequal mass ratio yet measured with gravitational waves,
0.112^+0.008 _0.009 , and its secondary component is either the
lightest black hole or the heaviest neutron star ever discovered in a
double compact-object system. The dimensionless spin of the primary
black hole is tightly constrained to 0.07. Tests of general relativity
reveal no measurable deviations from the theory, and its prediction of
higher-multipole emission is confirmed at high confidence. We estimate a
merger rate density of 1-23 Gpc^3 yr^1 for the new class of binary
coalescence sources that GW190814 represents. Astrophysical models
predict that binaries with mass ratios similar to this event can form
through several channels, but are unlikely to have formed in globular
clusters. However, the combination of mass ratio, component masses, and
the inferred merger rate for this event challenges all current models
for the formation and mass distribution of compact-object binaries.
Accepted by ApJ Letters
----------------------------------------------------------------
arXiv:2007.14251 astro-ph.HE gr-qc
*Gravitational-wave constraints on the equatorial ellipticity of
millisecond pulsars *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration.
Abstract: We present a search for continuous gravitational waves from
five radio pulsars, comprising three recycled pulsars (PSR J0437-4715,
PSR J0711-6830, and PSR J0737-3039A) and two young pulsars: the Crab
pulsar (J0534+2200) and the Vela pulsar (J0835-4510). We use data from
the third observing run of Advanced LIGO and Virgo combined with data
from their first and second observing runs. For the first time we are
able to match (for PSR J0437-4715) or surpass (for PSR J0711-6830) the
indirect limits on gravitational-wave emission from recycled pulsars
inferred from their observed spin-downs, and constrain their equatorial
ellipticities to be less than 10^8 . For each of the five pulsars, we
perform targeted searches that assume a tight coupling between the
gravitational-wave and electromagnetic signal phase evolution. We also
present constraints on PSR J0711-6830, the Crab pulsar and the Vela
pulsar from a search that relaxes this assumption, allowing the
gravitational-wave signal to vary from the electromagnetic expectation
within a narrow band of frequencies and frequency derivatives.
Journal reference: 2020 ApJL 902 L21
----------------------------------------------------------------
arXiv:2009.01190 astro-ph.HE gr-qc
*Properties and astrophysical implications of the 150 Msun binary black
hole merger GW190521 *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration.
Abstract: The gravitational-wave signal GW190521 is consistent with a
binary black hole merger source at redshift 0.8 with unusually high
component masses, 85^+21 _14 Mand 66^+17 _18 M, compared to
previously reported events, and shows mild evidence for spin-induced
orbital precession. The primary falls in the mass gap predicted by
(pulsational) pair-instability supernova theory, in the approximate
range 65120M. The probability that at least one of the black holes in
GW190521 is in that range is 99.0%. The final mass of the merger
(142^+28 _16 M) classifies it as an intermediate-mass black hole.
Under the assumption of a quasi-circular binary black hole coalescence,
we detail the physical properties of GW190521's source binary and its
post-merger remnant, including component masses and spin vectors. Three
different waveform models, as well as direct comparison to numerical
solutions of general relativity, yield consistent estimates of these
properties. Tests of strong-field general relativity targeting the
merger-ringdown stages of coalescence indicate consistency of the
observed signal with theoretical predictions. We estimate the merger
rate of similar systems to be 0.13^+0.30 _0.11 Gpc^3 yr^1 . We
discuss the astrophysical implications of GW190521 for stellar collapse,
and for the possible formation of black holes in the pair-instability
mass gap through various channels: via (multiple) stellar coalescence,
or via hierarchical merger of lower-mass black holes in star clusters or
in active galactic nuclei. We find it to be unlikely that GW190521 is a
strongly lensed signal of a lower-mass black hole binary merger. We also
discuss more exotic possible sources for GW190521, including a highly
eccentric black hole binary, or a primordial black hole binary.
Journal reference: Astrophys. J. Lett. 900, L13 (2020)
----------------------------------------------------------------
arXiv:2010.14527 gr-qc astro-ph.HE
*GWTC-2: Compact Binary Coalescences Observed by LIGO and Virgo During
the First Half of the Third Observing Run *
*Authors*: R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, K. Ackley,
A. Adams, C. Adams, R. X. Adhikari, V. B. Adya, C. Affeldt, M. Agathos,
K. Agatsuma, N. Aggarwal, O. D. Aguiar, L. Aiello, A. Ain, P. Ajith, S.
Akcay, G. Allen, A. Allocca, P. A. Altin, A. Amato, S. Anand, A.
Ananyeva, S. B. Anderson , et al. (1327 additional authors not shown)
Abstract: We report on gravitational wave discoveries from compact
binary coalescences detected by Advanced LIGO and Advanced Virgo in the
first half of the third observing run (O3a) between 1 April 2019 15:00
UTC and 1 October 2019 15:00. By imposing a false-alarm-rate threshold
of two per year in each of the four search pipelines that constitute our
search, we present 39 candidate gravitational wave events. At this
threshold, we expect a contamination fraction of less than 10%. Of
these, 26 candidate events were reported previously in near real-time
through GCN Notices and Circulars; 13 are reported here for the first
time. The catalog contains events whose sources are black hole binary
mergers up to a redshift of ~0.8, as well as events whose components
could not be unambiguously identified as black holes or neutron stars.
For the latter group, we are unable to determine the nature based on
estimates of the component masses and spins from gravitational wave data
alone. The range of candidate events which are unambiguously identified
as binary black holes (both objects 3 M) is increased compared to
GWTC-1, with total masses from 14 Mfor GW190924_021846 to 150 Mfor
GW190521. For the first time, this catalog includes binary systems with
significantly asymmetric mass ratios, which had not been observed in
data taken before April 2019. We also find that 11 of the 39 events
detected since April 2019 have positive effective inspiral spins under
our default prior (at 90% credibility), while none exhibit negative
effective inspiral spin. Given the increased sensitivity of Advanced
LIGO and Advanced Virgo, the detection of 39 candidate events in ~26
weeks of data (~1.5 per week) is consistent with GWTC-1.
Journal reference: Phys. Rev. X 11, 021053 (2021)
----------------------------------------------------------------
arXiv:2010.14529 gr-qc astro-ph.HE
*Tests of General Relativity with Binary Black Holes from the second
LIGO-Virgo Gravitational-Wave Transient Catalog *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration.
Abstract: Gravitational waves enable tests of general relativity in the
highly dynamical and strong-field regime. Using events detected by
LIGO-Virgo up to 1 October 2019, we evaluate the consistency of the data
with predictions from the theory. We first establish that residuals from
the best-fit waveform are consistent with detector noise, and that the
low- and high-frequency parts of the signals are in agreement. We then
consider parametrized modifications to the waveform by varying
post-Newtonian and phenomenological coefficients, improving past
constraints by factors of 2; we also find consistency with Kerr black
holes when we specifically target signatures of the spin-induced
quadrupole moment. Looking for gravitational-wave dispersion, we tighten
constraints on Lorentz-violating coefficients by a factor of 2.6 and
bound the mass of the graviton to mg1.76×10^23 eV/c^2 with 90%
credibility. We also analyze the properties of the merger remnants by
measuring ringdown frequencies and damping times, constraining
fractional deviations away from the Kerr frequency to f_220 =0.03^+0.38
_0.35 for the fundamental quadrupolar mode, and f_221 =0.04^+0.27
_0.32 for the first overtone; additionally, we find no evidence for
postmerger echoes. Finally, we determine that our data are consistent
with tensorial polarizations through a template-independent method. When
possible, we assess the validity of general relativity based on
collections of events analyzed jointly. We find no evidence for new
physics beyond general relativity, for black hole mimickers, or for any
unaccounted systematics.
Journal reference: Phys. Rev. D 103, 122002 (2021)
----------------------------------------------------------------
arXiv:2010.14533 astro-ph.HE gr-qc
*Population Properties of Compact Objects from the Second LIGO-Virgo
Gravitational-Wave Transient Catalog *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration.
Abstract: We report on the population of the 47 compact binary mergers
detected with a false-alarm rate 1/yr in the second LIGO--Virgo
Gravitational-Wave Transient Catalog, GWTC-2. We observe several
characteristics of the merging binary black hole (BBH) population not
discernible until now. First, we find that the primary mass spectrum
contains structure beyond a power-law with a sharp high-mass cut-off; it
is more consistent with a broken power law with a break at 39.7^+20.3
_9.1 M, or a power law with a Gaussian feature peaking at 33.1^+4.0
_5.6 M(90% credible interval). While the primary mass distribution
must extend to 65Mor beyond, only 2.9^+3.5 _-1.7 % of systems have
primary masses greater than 45M. Second, we find that a fraction of BBH
systems have component spins misaligned with the orbital angular
momentum, giving rise to precession of the orbital plane. Moreover, 12%
to 44% of BBH systems have spins tilted by more than 90, giving rise to
a negative effective inspiral spin parameter _eff . Under the
assumption that such systems can only be formed by dynamical
interactions, we infer that between 25% and 93% of BBH with
non-vanishing |_eff |>0.01 are dynamically assembled. Third, we
estimate merger rates, finding RBBH=23.9^+14.3 _-8.6 Gpc^3 yr^1 for
BBH and RBNS=320^+490 _240 Gpc^3 yr^1 for binary neutron stars. We
find that the BBH rate likely increases with redshift (85% credibility),
but not faster than the star-formation rate (86% credibility).
Additionally, we examine recent exceptional events in the context of our
population models, finding that the asymmetric masses of GW190412 and
the high component masses of GW190521 are consistent with our models,
but the low secondary mass of GW190814 makes it an outlier.
----------------------------------------------------------------
arXiv:2010.14550 astro-ph.HE gr-qc
*Search for Gravitational Waves Associated with Gamma-Ray Bursts
Detected by Fermi and Swift During the LIGO-Virgo Run O3a *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration.
Abstract: We search for gravitational-wave transients associated with
gamma-ray bursts detected by the Fermi and Swift satellites during the
first part of the third observing run of Advanced LIGO and Advanced
Virgo (1 April 2019 15:00 UTC - 1 October 2019 15:00 UTC). 105 gamma-ray
bursts were analyzed using a search for generic gravitational-wave
transients; 32 gamma-ray bursts were analyzed with a search that
specifically targets neutron star binary mergers as short gamma-ray
burst progenitors. We describe a method to calculate the probability
that triggers from the binary merger targeted search are astrophysical
and apply that method to the most significant gamma-ray bursts in that
search. We find no significant evidence for gravitational-wave signals
associated with the gamma-ray bursts that we followed up, nor for a
population of unidentified subthreshold signals. We consider several
source types and signal morphologies, and report for these lower bounds
on the distance to each gamma-ray burst.
Journal reference: Astrophys. J. 915, 86 (2021)
----------------------------------------------------------------
arXiv:2012.12128 gr-qc astro-ph.HE
*All-sky search in early O3 LIGO data for continuous gravitational-wave
signals from unknown neutron stars in binary systems *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration.
Abstract: Rapidly spinning neutron stars are promising sources of
persistent, continuous gravitational waves. Detecting such a signal
would allow probing of the physical properties of matter under extreme
conditions. A significant fraction of the known pulsar population
belongs to binary systems. Searching for unknown neutron stars in binary
systems requires specialized algorithms to address unknown orbital
frequency modulations. We present a search for continuous gravitational
waves emitted by neutron stars in binary systems in early data from the
third observing run of the Advanced LIGO and Advanced Virgo detectors
using the semicoherent, GPU-accelerated, BinarySkyHough pipeline. The
search analyzes the most sensitive frequency band of the LIGO detectors,
50 - 300 Hz. Binary orbital parameters are split into four regions,
comprising orbital periods of 3 - 45 days and projected semimajor axes
of 2 - 40 light-seconds. No detections are reported. We estimate the
sensitivity of the search using simulated continuous wave signals,
achieving the most sensitive results to date across the analyzed
parameter space.
Journal reference: Phys. Rev. D 103, 064017 (2021)
----------------------------------------------------------------
arXiv:2012.12926 astro-ph.HE gr-qc
Diving below the spin-down limit: Constraints on gravitational waves
from the energetic young pulsar PSR J0537-6910
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration.
Abstract: We present a search for continuous gravitational-wave signals
from the young, energetic X-ray pulsar PSR J0537-6910 using data from
the second and third observing runs of LIGO and Virgo. The search is
enabled by a contemporaneous timing ephemeris obtained using NICER data.
The NICER ephemeris has also been extended through 2020 October and
includes three new glitches. PSR J0537-6910 has the largest spin-down
luminosity of any pulsar and is highly active with regards to glitches.
Analyses of its long-term and inter-glitch braking indices provided
intriguing evidence that its spin-down energy budget may include
gravitational-wave emission from a time-varying mass quadrupole moment.
Its 62 Hz rotation frequency also puts its possible gravitational-wave
emission in the most sensitive band of LIGO/Virgo detectors. Motivated
by these considerations, we search for gravitational-wave emission at
both once and twice the rotation frequency. We find no signal, however,
and report our upper limits. Assuming a rigidly rotating triaxial star,
our constraints reach below the gravitational-wave spin-down limit for
this star for the first time by more than a factor of two and limit
gravitational waves from the l=m=2 mode to account for less than 14% of
the spin-down energy budget. The fiducial equatorial ellipticity is
limited to less than about 3e-5, which is the third best constraint for
any young pulsar.
----------------------------------------------------------------
arXiv:2101.11673 astro-ph.IM gr-qc
*LIGO Detector Characterization in the Second and Third Observing Runs *
*Authors*: D. Davis, J. S. Areeda, B. K. Berger, R. Bruntz, A. Effler,
R. C. Essick, R. P. Fisher, P. Godwin, E. Goetz, A. F. Helmling-Cornell,
B. Hughey, E. Katsavounidis, A. P. Lundgren, D. M. Macleod, Z. Márka, T.
J. Massinger, A. Matas, J. McIver, G. Mo, K. Mogushi, P. Nguyen, L. K.
Nuttall, R. M. S. Schofield, D. H. Shoemaker, S. Soni , et al. (262
additional authors not shown)
Abstract: The characterization of the Advanced LIGO detectors in the
second and third observing runs has increased the sensitivity of the
instruments, allowing for a higher number of detectable
gravitational-wave signals, and provided confirmation of all observed
gravitational-wave events. In this work, we present the methods used to
characterize the LIGO detectors and curate the publicly available
datasets, including the LIGO strain data and data quality products. We
describe the essential role of these datasets in LIGO-Virgo
Collaboration analyses of gravitational-waves from both transient and
persistent sources and include details on the provenance of these
datasets in order to support analyses of LIGO data by the broader
community. Finally, we explain anticipated changes in the role of
detector characterization and current efforts to prepare for the high
rate of gravitational-wave alerts and events in future observing runs.
Journal reference: Class. Quantum Grav. 38 135014 (2021)
----------------------------------------------------------------
arXiv:2101.12130 gr-qc astro-ph.CO
*Upper Limits on the Isotropic Gravitational-Wave Background from
Advanced LIGO's and Advanced Virgo's Third Observing Run *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: We report results of a search for an isotropic
gravitational-wave background (GWB) using data from Advanced LIGO's and
Advanced Virgo's third observing run (O3) combined with upper limits
from the earlier O1 and O2 runs. Unlike in previous observing runs in
the advanced detector era, we include Virgo in the search for the GWB.
The results are consistent with uncorrelated noise, and therefore we
place upper limits on the strength of the GWB. We find that the
dimensionless energy density GW5.8×109 at the 95% credible level for
a flat (frequency-independent) GWB, using a prior which is uniform in
the log of the strength of the GWB, with 99% of the sensitivity coming
from the band 20-76.6 Hz; 3.4×109 at 25 Hz for a power-law GWB with a
spectral index of 2/3 (consistent with expectations for compact binary
coalescences), in the band 20-90.6 Hz; and 3.9×1010 at 25 Hz for a
spectral index of 3, in the band 20-291.6 Hz. These upper limits improve
over our previous results by a factor of 6.0 for a flat GWB. We also
search for a GWB arising from scalar and vector modes, which are
predicted by alternative theories of gravity; we place upper limits on
the strength of GWBs with these polarizations. We demonstrate that there
is no evidence of correlated noise of magnetic origin by performing a
Bayesian analysis that allows for the presence of both a GWB and an
effective magnetic background arising from geophysical Schumann
resonances. We compare our upper limits to a fiducial model for the GWB
from the merger of compact binaries. Finally, we combine our results
with observations of individual mergers andshow that, at design
sensitivity, this joint approach may yield stronger constraints on the
merger rate of binary black holes at z2 than can be achieved with
individually resolved mergers alone. [abridged]
Journal reference: Phys. Rev. D 104, 022004 (2021)
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arXiv:2101.12248 gr-qc astro-ph.CO hep-th
*Constraints on cosmic strings using data from the third Advanced
LIGO-Virgo observing run *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: We search for gravitational-wave signals produced by cosmic
strings in the Advanced LIGO and Virgo full O3 data set. Search results
are presented for gravitational waves produced by cosmic string loop
features such as cusps, kinks and, for the first time, kink-kink
collisions.cA template-based search for short-duration transient signals
does not yield a detection. We also use the stochastic
gravitational-wave background energy density upper limits derived from
the O3 data to constrain the cosmic string tension, G, as a function of
the number of kinks, or the number of cusps, for two cosmic string loop
distribution models.cAdditionally, we develop and test a third model
which interpolates between these two models. Our results improve upon
the previous LIGO-Virgo constraints on G by one to two orders of
magnitude depending on the model which is tested. In particular, for one
loop distribution model, we set the most competitive constraints to
date, G4×10^15 .
Journal reference: Phys. Rev. Lett. 126, 241102 (2021)
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arXiv:2103.08520 gr-qc
*Search for anisotropic gravitational-wave backgrounds using data from
Advanced LIGO and Advanced Virgo's first three observing runs *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: We report results from searches for anisotropic stochastic
gravitational-wave backgrounds using data from the first three observing
runs of the Advanced LIGO and Advanced Virgo detectors. For the first
time, we include Virgo data in our analysis and run our search with a
new efficient pipeline called {\tt PyStoch} on data folded over one
sidereal day. We use gravitational-wave radiometry (broadband and narrow
band) to produce sky maps of stochastic gravitational-wave backgrounds
and to search for gravitational waves from point sources. A spherical
harmonic decomposition method is employed to look for gravitational-wave
emission from spatially-extended sources. Neither technique found
evidence of gravitational-wave signals. Hence we derive 95\%
confidence-level upper limit sky maps on the gravitational-wave energy
flux from broadband point sources, ranging from F_, <(0.0137.6)×10^8
ergcm^2 s^1 Hz^1 , and on the (normalized) gravitational-wave energy
density spectrum from extended sources, ranging from _,
<(0.579.3)×10^9 sr^1 , depending on direction () and spectral index
(). These limits improve upon previous limits by factors of 2.93.5. We
also set 95% confidence level upper limits on the frequency-dependent
strain amplitudes of quasimonochromatic gravitational waves coming from
three interesting targets, Scorpius X-1, SN 1987A and the Galactic
Center, with best upper limits range from h_0 <(1.72.1)×10^25 , a
factor of 2.0 improvement compared to previous stochastic radiometer
searches.
Journal reference: Phys. Rev. D 104, 022005 (2021)
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arXiv:2104.14417 astro-ph.HE gr-qc
*Constraints from LIGO O3 data on gravitational-wave emission due to
r-modes in the glitching pulsar PSR J0537-6910 *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: We present a search for continuous gravitational-wave emission
due to r-modes in the pulsar PSR J0537-6910 using data from the
LIGO-Virgo Collaboration observing run O3. PSR J0537-6910 is a young
energetic X-ray pulsar and is the most frequent glitcher known. The
inter-glitch braking index of the pulsar suggests that
gravitational-wave emission due to r-mode oscillations may play an
important role in the spin evolution of this pulsar. Theoretical models
confirm this possibility and predict emission at a level that can be
probed by ground-based detectors. In order to explore this scenario, we
search for r-mode emission in the epochs between glitches by using a
contemporaneous timing ephemeris obtained from NICER data. We do not
detect any signals in the theoretically expected band of 86-97 Hz, and
report upper limits on the amplitude of the gravitational waves. Our
results improve on previous amplitude upper limits from r-modes in
J0537-6910 by a factor of up to 3 and place stringent constraints on
theoretical models for r-mode driven spin-down in PSR J0537-6910,
especially for higher frequencies at which our results reach below the
spin-down limit defined by energy conservation.
Journal reference: ApJ 922 71 (2021)
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arXiv:2105.06384 gr-qc astro-ph.HE
*Search for lensing signatures in the gravitational-wave observations
from the first half of LIGO-Virgo's third observing run *
Authors: The LIGO Scientific Collaboration, the Virgo Collaboration.
Abstract: We search for signatures of gravitational lensing in the
gravitational-wave signals from compact binary coalescences detected by
Advanced LIGO and Advanced Virgo during O3a, the first half of their
third observing run. We study: 1) the expected rate of lensing at
current detector sensitivity and the implications of a non-observation
of strong lensing or a stochastic gravitational-wave background on the
merger-rate density at high redshift; 2) how the interpretation of
individual high-mass events would change if they were found to be
lensed; 3) the possibility of multiple images due to strong lensing by
galaxies or galaxy clusters; and 4) possible wave-optics effects due to
point-mass microlenses. Several pairs of signals in the multiple-image
analysis show similar parameters and, in this sense, are nominally
consistent with the strong lensing hypothesis. However, taking into
account population priors, selection effects, and the prior odds against
lensing, these events do not provide sufficient evidence for lensing.
Overall, we find no compelling evidence for lensing in the observed
gravitational-wave signals from any of these analyses.
----------------------------------------------------------------
arXiv:2105.07455 gr-qc
*An all-sky search in early O3 LIGO data for continuous
gravitational-wave signals from unknown neutron stars in binary systems *
Authors: LIGO Scientific Collaboration, Virgo Collaboration
Abstract: We present a search for continuous gravitational waves emitted
by neutron stars in binary systems conducted on data from the early
third observing run of the Advanced LIGO and Advanced Virgo detectors
using the semicoherent, GPU-accelerated, BinarySkyHough pipeline. The
search analyzes the most sensitive frequency band of the LIGO detectors,
50 - 300 Hz. Binary orbital parameters are split into four regions,
comprising orbital periods of 3 - 45 days and projected semimajor axes
of 2 - 40 light-seconds. No detections are reported. We estimate the
sensitivity of the search using simulated continuous wave signals,
achieving the most sensitive results to date across the analyzed
parameter space.
----------------------------------------------------------------
arXiv:2105.13085 astro-ph.CO gr-qc hep-ph
*Constraints on dark photon dark matter using data from LIGO's and
Virgo's third observing run *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: We present a search for dark photon dark matter that could
couple to gravitational-wave interferometers using data from Advanced
LIGO and Virgo's third observing run. To perform this analysis, we use
two methods, one based on cross-correlation of the strain channels in
the two nearly aligned LIGO detectors, and one that looks for excess
power in the strain channels of the LIGO and Virgo detectors. The excess
power method optimizes the Fourier Transform coherence time as a
function of frequency, to account for the expected signal width due to
Doppler modulations. We do not find any evidence of dark photon dark
matter with a mass between m_A 10^14 10^11 eV/c^2 , which
corresponds to frequencies between 10-2000 Hz, and therefore provide
upper limits on the square of the minimum coupling of dark photons to
baryons, i.e. U(1)B dark matter. For the cross-correlation method, the
best median constraint on the squared coupling is 1.31×10^47 at m_A
4.2×10^13 eV/c^2 ; for the other analysis, the best constraint is
1.2×10^47 at m_A 5.7×10^13 eV/c^2 . These limits improve upon those
obtained in direct dark matter detection experiments by a factor of 100
for m_A [24]×10^13 eV/c^2 .
----------------------------------------------------------------
arXiv:2105.15120 astro-ph.HE gr-qc
*Search for intermediate mass black hole binaries in the third observing
run of Advanced LIGO and Advanced Virgo *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: Intermediate-mass black holes (IMBHs) span the approximate
mass range 100--105M, between black holes (BHs) formed by stellar
collapse and the supermassive BHs at the centers of galaxies. Mergers of
IMBH binaries are the most energetic gravitational-wave sources
accessible by the terrestrial detector network. Searches of the first
two observing runs of Advanced LIGO and Advanced Virgo did not yield any
significant IMBH binary signals. In the third observing run (O3), the
increased network sensitivity enabled the detection of GW190521, a
signal consistent with a binary merger of mass 150Mproviding direct
evidence of IMBH formation. Here we report on a dedicated search of O3
data for further IMBH binary mergers, combining both modelled (matched
filter) and model independent search methods. We find some marginal
candidates, but none are sufficiently significant to indicate detection
of further IMBH mergers. We quantify the sensitivity of the individual
search methods and of the combined search using a suite of IMBH binary
signals obtained via numerical relativity, including the effects of
spins misaligned with the binary orbital axis, and present the resulting
upper limits on astrophysical merger rates. Our most stringent limit is
for equal mass and aligned spin BH binary of total mass 200Mand
effective aligned spin 0.8 at 0.056Gpc^3 yr^1 (90 % confidence), a
factor of 3.5 more constraining than previous LIGO-Virgo limits. We also
update the estimated rate of mergers similar to GW190521 to 0.08Gpc^3
yr^1 .
----------------------------------------------------------------
arXiv:2107.00600 gr-qc astro-ph.HE
*All-sky Search for Continuous Gravitational Waves from Isolated Neutron
Stars in the Early O3 LIGO Data *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: We report on an all-sky search for continuous gravitational
waves in the frequency band 20-2000\,Hz and with a frequency time
derivative in the range of [1.0,+0.1]×10^8 Hz/s. Such a signal could
be produced by a nearby, spinning and slightly non-axisymmetric isolated
neutron star in our galaxy. This search uses the LIGO data from the
first six months of Advanced LIGO's and Advanced Virgo's third
observational run, O3. No periodic gravitational wave signals are
observed, and 95%\ confidence-level (CL) frequentist upper limits are
placed on their strengths. The lowest upper limits on worst-case
(linearly polarized) strain amplitude h_0 are 1.7×10^25 near 200 Hz.
For a circularly polarized source (most favorable orientation), the
lowest upper limits are 6.3×10^26 . These strict frequentist upper
limits refer to all sky locations and the entire range of frequency
derivative values. For a population-averaged ensemble of sky locations
and stellar orientations, the lowest 95\%\ CL upper limits on the strain
amplitude are 1.×10^25 . These upper limits improve upon our
previously published all-sky results, with the greatest improvement
(factor of 2) seen at higher frequencies, in part because quantum
squeezing has dramatically improved the detector noise level relative to
the second observational run, O2. These limits are the most constraining
to date over most of the parameter space searched.
Journal reference: Phys. Rev. D 104, 082004 (2021)
----------------------------------------------------------------
arXiv:2107.03294 gr-qc astro-ph.IM
*Calibration of Advanced Virgo and reconstruction of detector strain
h(t) during the Observing Run O3 *
*Authors*: Virgo Collaboration.
Abstract: The three Advanced Virgo and LIGO gravitational wave detectors
participated to the third observing run (O3) between 1 April 2019 15:00
UTC and 27 March 2020 17:00 UTC,leading to several gravitational wave
detections per month. This paper describes the Advanced Virgo detector
calibration and the reconstruction of the detector strain h(t) during
O3, as well as the estimation of the associated uncertainties. For the
first time, the photon calibration technique as been used as reference
for Virgo calibration, which allowed to cross-calibrate the strain
amplitude of the Virgo and LIGO detectors. The previous reference,
so-called free swinging Michelson technique, has still been used but as
an independent cross-check. h(t) reconstruction and noise subtraction
were processed online, with good enough quality to prevent the need for
offline reprocessing, except for the two last weeks of September 2019.
The uncertainties for the reconstructed h(t) strain, estimated in this
paper in a 20-2000~Hz frequency band, are frequency independent: 5% in
amplitude, 35 mrad in phase and 10 s in timing, with the exception of
larger uncertainties around 50 Hz.
----------------------------------------------------------------
arXiv:2107.03701 gr-qc astro-ph.HE
*All-sky search for short gravitational-wave bursts in the third
Advanced LIGO and Advanced Virgo run *
Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, the
KAGRA Collaboration.
Abstract: This paper presents the results of a search for generic
short-duration gravitational-wave transients in data from the third
observing run of Advanced LIGO and Advanced Virgo. Transients with
durations of milliseconds to a few seconds in the 24--4096 Hz frequency
band are targeted by the search, with no assumptions made regarding the
incoming signal direction, polarization or morphology. Gravitational
waves from compact binary coalescences that have been identified by
other targeted analyses are detected, but no statistically significant
evidence for other gravitational wave bursts is found. Sensitivities to
a variety of signals are presented. These include updated upper limits
on the source rate-density as a function of the characteristic frequency
of the signal, which are roughly an order of magnitude better than
previous upper limits. This search is sensitive to sources radiating as
little as 10^10 Mc^2 in gravitational waves at 70 Hz from a distance
of 10 kpc, with 50% detection efficiency at a false alarm rate of one
per century. The sensitivity of this search to two plausible
astrophysical sources is estimated: neutron star f-modes, which may be
excited by pulsar glitches, as well as selected core-collapse supernova
models.
----------------------------------------------------------------
arXiv:2107.13796 gr-qc astro-ph.HE
*All-sky search for long-duration gravitational-wave bursts in the third
Advanced LIGO and Advanced Virgo run *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: After the detection of gravitational waves from compact binary
coalescences, the search for transient gravitational-wave signals with
less well-defined waveforms for which matched filtering is not
well-suited is one of the frontiers for gravitational-wave astronomy.
Broadly classified into "short" 1 s and "long" 1 s duration signals,
these signals are expected from a variety of astrophysical processes,
including non-axisymmetric deformations in magnetars or eccentric binary
black hole coalescences. In this work, we present a search for
long-duration gravitational-wave transients from Advanced LIGO and
Advanced Virgo's third observing run from April 2019 to March 2020. For
this search, we use minimal assumptions for the sky location, event
time, waveform morphology, and duration of the source. The search covers
the range of 2 500 s in duration and a frequency band of 242048 Hz.
We find no significant triggers within this parameter space; we report
sensitivity limits on the signal strength of gravitational waves
characterized by the root-sum-square amplitude hrss as a function of
waveform morphology. These hrss limits improve upon the results from the
second observing run by an average factor of 1.8.
----------------------------------------------------------------
arXiv:2108.01045 gr-qc
*GWTC-2.1: Deep Extended Catalog of Compact Binary Coalescences Observed
by LIGO and Virgo During the First Half of the Third Observing Run *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
R. Abbott, T. D. Abbott, F. Acernese, K. Ackley, C. Adams, N. Adhikari,
R. X. Adhikari, V. B. Adya, C. Affeldt, D. Agarwal, M. Agathos, K.
Agatsuma, N. Aggarwal, O. D. Aguiar, L. Aiello, A. Ain, P. Ajith, S.
Albanesi, A. Allocca, P. A. Altin, A. Amato, C. Anand, S. Anand , et al.
(1407 additional authors not shown)
Abstract: The second gravitational-wave transient catalog, GWTC-2,
reported on 39 compact binary coalescences observed by the Advanced LIGO
and Advanced Virgo detectors between 1 April 2019 15:00 UTC and 1
October 2019 15:00 UTC. Here, we present GWTC-2.1, which reports on a
deeper list of candidate events observed over the same period. We
analyze the final version of the strain data over this period, which is
now publicly released. We employ three matched-filter search pipelines
for candidate identification, and estimate the probability of
astrophysical origin for each candidate event. While GWTC-2 used a false
alarm rate threshold of 2 per year, we include in GWTC-2.1, 1201
candidates that pass a false alarm rate threshold of 2 per day. We
calculate the source properties of a subset of 44 high-significance
candidates that have a probability of astrophysical origin greater than
0.5, using the default priors. Of these candidates, 36 have been
reported in GWTC-2. If the 8 additional high-significance candidates
presented here are astrophysical, the mass range of candidate events
that are unambiguously identified as binary black holes (both objects
3M) is increased compared to GWTC-2, with total masses from 14Mfor
GW190924_021846 to 184Mfor GW190426_190642. The primary components of
two new candidate events (GW190403_051519 and GW190426_190642) fall in
the mass gap predicted by pair-instability supernova theory. We also
expand the population of binaries with significantly asymmetric mass
ratios reported in GWTC-2 by an additional two events (q<0.61 and q<0.62
at 90% credibility for GW190403_051519 and GW190917_114630
respectively), and find that 2 of the 8 new events have effective
inspiral spins _eff >0 (at 90% credibility), while no binary is
consistent with _eff <0 at the same significance.
----------------------------------------------------------------
arXiv:2109.09255 astro-ph.HE gr-qc
*Search for continuous gravitational waves from 20 accreting millisecond
X-ray pulsars in O3 LIGO data *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: Results are presented of searches for continuous gravitational
waves from 20 accreting millisecond X-ray pulsars with accurately
measured spin frequencies and orbital parameters, using data from the
third observing run of the Advanced LIGO and Advanced Virgo detectors.
The search algorithm uses a hidden Markov model, where the transition
probabilities allow the frequency to wander according to an unbiased
random walk, while the J-statistic maximum-likelihood matched filter
tracks the binary orbital phase. Three narrow sub-bands are searched for
each target, centered on harmonics of the measured spin frequency. The
search yields 16 candidates, consistent with a false alarm probability
of 30% per sub-band and target searched. These candidates, along with
one candidate from an additional target-of-opportunity search done for
SAX J1808.43658, which was in outburst during one month of the
observing run, cannot be confidently associated with a known noise
source. Additional follow-up does not provide convincing evidence that
any are a true astrophysical signal. When all candidates are assumed
non-astrophysical, upper limits are set on the maximum wave strain
detectable at 95% confidence, h^95% _0 . The strictest constraint is
h^95% _0 =4.7×10^26 from IGR J170626143. Constraints on the detectable
wave strain from each target lead to constraints on neutron star
ellipticity and r-mode amplitude, the strictest of which are ^95%
=3.1×10^7 and ^95% =1.8×10^5 respectively. This analysis is the most
comprehensive and sensitive search of continuous gravitational waves
from accreting millisecond X-ray pulsars to date.
----------------------------------------------------------------
arXiv:2109.12197 astro-ph.CO astro-ph.HE gr-qc
*Search for subsolar-mass binaries in the first half of Advanced LIGO
and Virgo's third observing run *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: We report on a search for compact binary coalescences where at
least one binary component has a mass between 0.2 Mand 1.0 Min
Advanced LIGO and Advanced Virgo data collected between 1 April 2019
1500 UTC and 1 October 2019 1500 UTC. We extend previous analyses in two
main ways: we include data from the Virgo detector and we allow for more
unequal mass systems, with mass ratio q0.1. We do not report any
gravitational-wave candidates. The most significant trigger has a false
alarm rate of 0.14 yr^1 . This implies an upper limit on the merger
rate of subsolar binaries in the range [22024200]Gpc^3 yr^1 ,
depending on the chirp mass of the binary. We use this upper limit to
derive astrophysical constraints on two phenomenological models that
could produce subsolar-mass compact objects. One is an isotropic
distribution of equal-mass primordial black holes. Using this model, we
find that the fraction of dark matter in primordial black holes is f_PBH
_PBH /_DM 6%. The other is a dissipative dark matter model, in which
fermionic dark matter can collapse and form black holes. The upper limit
on the fraction of dark matter black holes depends on the minimum mass
of the black holes that can be formed: the most constraining result is
obtained at M_min =1M, where f_DBH _PBH /_DM 0.003%. These are the
tightest limits on spinning subsolar-mass binaries to date.
----------------------------------------------------------------
arXiv:2110.09834 gr-qc
*All-sky, all-frequency directional search for persistent
gravitational-waves from Advanced LIGO's and Advanced Virgo's first
three observing runs *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: We present the first results from an all-sky all-frequency
(ASAF) search for an anisotropic stochastic gravitational-wave
background using the data from the first three observing runs of the
Advanced LIGO and Advanced Virgo detectors. Upper limit maps on
broadband anisotropies of a persistent stochastic background were
published for all observing runs of the LIGO-Virgo detectors. However, a
broadband analysis is likely to miss narrowband signals as the
signal-to-noise ratio of a narrowband signal can be significantly
reduced when combined with detector output from other frequencies. Data
folding and the computationally efficient analysis pipeline, {\tt
PyStoch}, enable us to perform the radiometer map-making at every
frequency bin. We perform the search at 3072 {\tt{HEALPix}} equal area
pixels uniformly tiling the sky and in every frequency bin of width
1/32~Hz in the range 201726~Hz, except for bins that are likely to
contain instrumental artefacts and hence are notched. We do not find any
statistically significant evidence for the existence of narrowband
gravitational-wave signals in the analyzed frequency bins. Therefore, we
place 95% confidence upper limits on the gravitational-wave strain for
each pixel-frequency pair, the limits are in the range
(0.0309.6)×10^24 . In addition, we outline a method to identify
candidate pixel-frequency pairs that could be followed up by a more
sensitive (and potentially computationally expensive) search, e.g., a
matched-filtering-based analysis, to look for fainter nearly
monochromatic coherent signals. The ASAF analysis is inherently
independent of models describing any spectral or spatial distribution of
power. We demonstrate that the ASAF results can be appropriately
combined over frequencies and sky directions to successfully recover the
broadband directional and isotropic results.
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arXiv:2111.03604 astro-ph.CO gr-qc
*Constraints on the cosmic expansion history from GWTC-3 *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: We use 47 gravitational-wave sources from the Third
LIGO-Virgo-KAGRA Gravitational-Wave Transient Catalog (GWTC-3) to
estimate the Hubble parameter H(z), including its current value, the
Hubble constant H_0 . Each gravitational-wave (GW) signal provides the
luminosity distance to the source and we estimate the corresponding
redshift using two methods: the redshifted masses and a galaxy catalog.
Using the binary black hole (BBH) redshifted masses, we simultaneously
infer the source mass distribution and H(z). The source mass
distribution displays a peak around 34M, followed by a drop-off.
Assuming this mass scale does not evolve with redshift results in a H(z)
measurement, yielding H_0 =68^+12 _7 kms^1 Mpc^1 (68% credible
interval) when combined with the H_0 measurement from GW170817 and its
electromagnetic counterpart. This represents an improvement of 17% with
respect to the H_0 estimate from GWTC-1. The second method associates
each GW event with its probable host galaxy in the catalog GLADE+,
statistically marginalizing over the redshifts of each event's potential
hosts. Assuming a fixed BBH population, we estimate a value of H_0
=68^+8 _6 kms^1 Mpc^1 with the galaxy catalog method, an improvement
of 42% with respect to our GWTC-1 result and 20% with respect to recent
H_0 studies using GWTC-2 events. However, we show that this result is
strongly impacted by assumptions about the BBH source mass distribution;
the only event which is not strongly impacted by such assumptions (and
is thus informative about H_0 ) is the well-localized event GW190814.
----------------------------------------------------------------
arXiv:2111.03606 gr-qc astro-ph.HE
*GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo During
the Second Part of the Third Observing Run *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: The third Gravitational-wave Transient Catalog (GWTC-3)
describes signals detected with Advanced LIGO and Advanced Virgo up to
the end of their third observing run. Updating the previous GWTC-2.1, we
present candidate gravitational waves from compact binary coalescences
during the second half of the third observing run (O3b) between 1
November 2019, 15:00 UTC and 27 March 2020, 17:00 UTC. There are 35
compact binary coalescence candidates identified by at least one of our
search algorithms with a probability of astrophysical origin p_astro
>0.5. Of these, 18 were previously reported as low-latency public
alerts, and 17 are reported here for the first time. Based upon
estimates for the component masses, our O3b candidates with p_astro >0.5
are consistent with gravitational-wave signals from binary black holes
or neutron star-black hole binaries, and we identify none from binary
neutron stars. However, from the gravitational-wave data alone, we are
not able to measure matter effects that distinguish whether the binary
components are neutron stars or black holes. The range of inferred
component masses is similar to that found with previous catalogs, but
the O3b candidates include the first confident observations of neutron
star-black hole binaries. Including the 35 candidates from O3b in
addition to those from GWTC-2.1, GWTC-3 contains 90 candidates found by
our analysis with p_astro >0.5 across the first three observing runs.
These observations of compact binary coalescences present an
unprecedented view of the properties of black holes and neutron stars.
----------------------------------------------------------------
arXiv:2111.03608 astro-ph.HE gr-qc
*Search for Gravitational Waves Associated with Gamma-Ray Bursts
Detected by Fermi and Swift During the LIGO-Virgo Run O3b *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: We search for gravitational-wave signals associated with
gamma-ray bursts detected by the Fermi and Swift satellites during the
second half of the third observing run of Advanced LIGO and Advanced
Virgo (1 November 2019 15:00 UTC-27 March 2020 17:00 UTC).We conduct two
independent searches: a generic gravitational-wave transients search to
analyze 86 gamma-ray bursts and an analysis to target binary mergers
with at least one neutron star as short gamma-ray burst progenitors for
17 events. We find no significant evidence for gravitational-wave
signals associated with any of these gamma-ray bursts. A weighted
binomial test of the combined results finds no evidence for
sub-threshold gravitational wave signals associated with this GRB
ensemble either. We use several source types and signal morphologies
during the searches, resulting in lower bounds on the estimated distance
to each gamma-ray burst. Finally, we constrain the population of low
luminosity short gamma-ray bursts using results from the first to the
third observing runs of Advanced LIGO and Advanced Virgo. The resulting
population is in accordance with the local binary neutron star merger rate.
----------------------------------------------------------------
arXiv:2111.03634 astro-ph.HE gr-qc
*The population of merging compact binaries inferred using gravitational
waves through GWTC-3 *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: We report on the population properties of 76 compact binary
mergers detected with gravitational waves below a false alarm rate of 1
per year through GWTC-3. The catalog contains three classes of binary
mergers: BBH, BNS, and NSBH mergers. We infer the BNS merger rate to be
between 13 Gpc^3 yr^1 and 1900 Gpc^3 yr^1 and the NSBH merger rate
to be between 7.4 Gpc^3 yr^1 and 320 Gpc^3 yr^1 , assuming a
constant rate density versus comoving volume and taking the union of 90%
credible intervals for methods used in this work. Accounting for the BBH
merger rate to evolve with redshift, we find the BBH merger rate to be
between 17.3 Gpc^3 yr^1 and 45 Gpc^3 yr^1 at a fiducial redshift
(z=0.2). We obtain a broad neutron star mass distribution extending from
1.2^+0.1 _0.2 Mto 2.0^+0.3 _0.2 M. We can confidently identify a
rapid decrease in merger rate versus component mass between neutron
star-like masses and black-hole-like masses, but there is no evidence
that the merger rate increases again before 10 M. We also find the BBH
mass distribution has localized over- and under-densities relative to a
power law distribution. While we continue to find the mass distribution
of a binary's more massive component strongly decreases as a function of
primary mass, we observe no evidence of a strongly suppressed merger
rate above 60M. The rate of BBH mergers is observed to increase with
redshift at a rate proportional to (1+z)^|| with =2.7^+1.8 _1.9 for
z1. Observed black hole spins are small, with half of spin magnitudes
below _i 0.26. We observe evidence of negative aligned spins in the
population, and an increase in spin magnitude for systems with more
unequal mass ratio.
----------------------------------------------------------------
arXiv:2111.13106 astro-ph.HE gr-qc
*Searches for Gravitational Waves from Known Pulsars at Two Harmonics in
the Second and Third LIGO-Virgo Observing Runs *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration,
the KAGRA Collaboration.
Abstract: We present a targeted search for continuous gravitational
waves (GWs) from 236 pulsars using data from the third observing run of
LIGO and Virgo (O3) combined with data from the second observing run
(O2). Searches were for emission from the l=m=2 mass quadrupole mode
with a frequency at only twice the pulsar rotation frequency (single
harmonic) and the l=2,m=1,2 modes with a frequency of both once and
twice the rotation frequency (dual harmonic). No evidence of GWs was
found so we present 95% credible upper limits on the strain amplitudes
h_0 for the single harmonic search along with limits on the pulsars'
mass quadrupole moments Q_22 and ellipticities . Of the pulsars
studied, 23 have strain amplitudes that are lower than the limits
calculated from their electromagnetically measured spin-down rates.
These pulsars include the millisecond pulsars J0437-4715 and J0711-6830
which have spin-down ratios of 0.87 and 0.57 respectively. For nine
pulsars, their spin-down limits have been surpassed for the first time.
For the Crab and Vela pulsars our limits are factors of 100 and 20
more constraining than their spin-down limits, respectively. For the
dual harmonic searches, new limits are placed on the strain amplitudes
C_21 and C_22 . For 23 pulsars we also present limits on the emission
amplitude assuming dipole radiation as predicted by Brans-Dicke theory.
----------------------------------------------------------------
arXiv:2111.15116 gr-qc
*Search of the Early O3 LIGO Data for Continuous Gravitational Waves
from the Cassiopeia A and Vela Jr. Supernova Remnants *
*Authors*: The LIGO Scientific Collaboration, the Virgo Collaboration.
Abstract: We present directed searches for continuous gravitational
waves from the neutron stars in the Cassiopeia A (Cas A) and Vela Jr.
supernova remnants. We carry out the searches in the LIGO data from the
first six months of the third Advanced LIGO and Virgo observing run,
using the Weave semi-coherent method, which sums matched-filter
detection-statistic values over many time segments spanning the
observation period. No gravitational wave signal is detected in the
search band of 20--976 Hz for assumed source ages greater than 300 years
for Cas A and greater than 700 years for Vela Jr. Estimates from
simulated continuous wave signals indicate we achieve the most sensitive
results to date across the explored parameter space volume, probing to
strain magnitudes as low as ~6.3×10^26 for Cas A and ~5.6×10^26 for
Vela Jr. at frequencies near 166 Hz at 95% efficiency.
******************************************************************************