Subject: ASGRG Newsletter #19
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AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION
Electronic Newsletter -- #19, Winter 2011
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Items for this newsletter should be emailed to the editor:
asgrg *AT* hotmail *DOT* com
The deadline for the next issue is 30 June, 2012.
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CONTENTS:
* REPORT ON ACGRG5, Christchurch, 16-18 December, 2009
* MINUTES OF THE 6TH BIENNIAL GENERAL MEETING OF THE ASGRG
16 December 2009
* ACGRG6, University of Adelaide, February 2012
* 7th BIENNIAL GENERAL MEETING OF THE ASGRG
Febrary 2012
* 20th CONGRESS OF THE AUSTRALIAN INSTITUTE OF PHYSICS
Sydney Convention Centre, 9-13 December 2012
* MEMBERSHIP DETAILS ONLINE at
http://www.physics.adelaide.edu.au/ASGRG/members.html
* SUBSCRIPTIONS
* FORTHCOMING MEETINGS
* MEMBERS' ABSTRACTS at gr-qc, December 2008 - June 2011
* ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc,
December 2008 - June 2011
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REPORT ON ACGRG5, University of Canterbury, Christchurch, December 16-18 2009
The 5th Australasian Conference on General Relativity and Gravitation (ACGRG5)
was held at the University of Canterbury in Christchurch, New Zealand from 16
to 18 December 2009. ACGRG5 was the fifth in a series of approximately
biennial conferences on general relativity and gravitation organised by the
ASGRG.
A total of 42 presentations were given over the three days of ACGRG5,
including plenary talks from Ju Li ("Towards the southern hemisphere
gravitational wave detector: Technology, the science case for AIGO and recent
progress"), Leo Brewin ("Non-standard computational methods in numerical
relativity"), Matt Visser ("Who's afraid of Lorentz symmetry breaking"),
Susan Scott ("Encoding cosmological futures with conformal structure"), Dick
Manchester ("Detection of gravitational waves with pulsar timing"), Joerg
Frauendiener ("Conceptual issues in numerical relativity"), Ra Inta ("Catching
a wave: Interesting science discovered en route to the detection of
gravitational waves using ground-based laser interferometers"), David
Wiltshire ("Dark energy without dark energy") and Lev Titarchuk
("Determination of black hole masses in galactic black hole binaries").
In addition, Roy Kerr delivered a public lecture on the evening of December
16 entitled "Cracking the Einstein code", which was full of interesting
anecdotes about his discovery of the Kerr metric in 1963.
The more specialised talks at ACGRG5 covered topics as diverse as gravitational
wave detection technology, Kodama time, the Alcubierre warp drive, the Holst
formulation of gravity, warped compactification, Brans-Dicke cosmology,
Kerr-Newman-de Sitter spacetimes, Krolak strong curvature conditions, numerical
differential geometry, impulsive vacuum spacetimes, accelerated objects,
neutrino oscillations, fermionic dark matter, Snyder geometry, the integrated
Sachs-Wolfe effect, supernovae, cluster formation, measuring the solar diameter,
the Kerr-Schild ansatz and black holes in cosmological backgrounds.
The final event on the closing day, December 18, was the first ever award of
the Kerr Prize, to mark the best student presentation at an ACGRG. The judges
decided on this occasion to split the prize between Maya Watanabe of Monash
University, who spoke about "Electrodynamics around Schwarzschild and Reissner-
Nordstrom black holes", and Richard Barry of the Australian National
University, whose talk was entitled "A topology for the abstract boundary
construction for space-time". The two winners shared the $100 prize, and
enjoyed a photo opportunity with Roy Kerr.
The conference banquet was held at the University of Canterbury Staff Club
(the Ilam Homestead) on the evening of December 17, and made for a very
pleasant interlude. Particular thanks should go to the local organisers
(David Wiltshire, Roy Kerr, Maria Mattsson, Teppo Mattsson, Ishwaree
Neupane and Peter Smale) for making ACGRG5 such an enjoyable experience.
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MINUTES OF THE 6TH BIENNIAL GENERAL MEETING OF THE ASGRG
held at the University of Christchurch, Canterbury, 16 December, 2009
The meeting opened at 5.35 p.m.
[16 ASGRG members were present. At the time of the BGM 58 of the members
were financial, so the meeting was quorate.]
Apologies: John Schutz
1. The minutes of the 5th Biennial General Meeting, held at the Sydney
Convention and Exhibition Centre, 12 July 2007, were presented to the
meeting. John Steele moved that the minutes be accepted, and Leo Brewin
seconded. The motion was approved.
2. President's Report: Susan Scott described the period from 2007 to 2009
as "the most happening three years" in the history of the ASGRG. THe
highlight was the hosting of the combined GR18 and Amaldi7 meetings at
the Sydney Convention and Exhibition Centre from 8 to 14 July 2007. The
two conferences together drew 520 participants, and there wre public
lectures from such luminaries as Prof Sir Roger Penrose and Prof Kip Thorne.
The only downside of the event was that it made a financial loss. The
budgeted minimum number of participants was 600, and the main reason cited
by the ISGRG for the shortfall was the high cost of air travel to Australia.
The overall deficit was $35,000, of which $20,000 was underwritten by the
Australian Institute of Physics and another $5,000 by the ASGRG. Total
sponsorship came to $150,000, with money from the ANU, BHP, Maple, Springer
and the AMSI, but there was no support from the Australian Government.
The proceedings of the two meetings have now been published. For GR18, the
proceedings have appeared as Class. Quant. Grav. 25, 110201 (2008), while
the proceedings of Amaldi7 are in J. Phys. Conf. Ser. 122, 011001 (2008).
The editors of both volumes are Susan Scott and David McClelland.
Other events mentioned by Susan included the Australian Mathematical
Sciences Institute (AMSI) Workshop on Mathematical General Relativity held
at Melbourne University in July 2008, whose chief organiser was Con
Lozanovski, and the 18th Biennial Congress of the AIP in Adelaide in
December 2008, at which Steve Carlip was a plenary speaker and the ASGRG
ran three parallel sessions.
In addition, the Australian Consortium for Interferometric Gravitational
Astronomy (ACIGA) has been very active over the last three years, with
ACIGA members participating in the final year of the S5 science run of the
LIGO gravitational wave detectors, and winning a LIEF grant to develop
AIGO in Gingin in 2007. ACIGA became a full partner in Advanced LIGO in
2008, and in the same year LIGO and VIRGO joined forces to form the LIG0-
VIRGO Collaboration.
Finally, Susan reported that the AIP Women in Physics Lecturer for 2010
would be Prof. Elizabeth Winstanley of the University of Sheffield, and
bade everyone to make her welcome.
3. Treasurer's Report: John Steele reported that immediately before
the start of ACGRG5 the Society had a total of 58 financial members, of
which 40 were life members, 5 were ordinary members and 11 were student
members, plus 50 to 55 non-financial members.
The Society's current account contained $13,098, and there was a debt
residue from GR18/Amaldi7 of $4,982.
John also reported that the main expense of the Society was bank fees. A
number of suggestions were made from the floor to remedy this problem.
One was to use Statepay (statepay.com.au) to process card payments
(although ASGRG has no ABN), and another was to use PayPal. It was also
suggested that the Society put $5,000 of its funds in a term deposit. John
promised to investigate all these possibilities.
4. Auditor's Report: The Auditor, John Schutz, certified in an email that he
was satisfied with the Society's accounts. David Wiltshire moved that the
ASGRG accept the accounts, and Matt Visser seconded. The motion was approved.
5. Appointment of Auditor for the next session: John Steele nominated John
Schutz to remain the Auditor of the Society's accounts, and Leo Brewin
seconded. The Secretary was asked to check that John Schutz is happy to
continue as Auditor.
6. Date and venue for ACGRG6: The meeting decided (tentatively) that ACGRG6
would be held at the University of Adelaide in the summer of 2011-12. The
Secretary was asked to contact Peter Veitch at the University of Adelaide
and confirm that he is willing to chair the Local Organising Committee.
7. Election of officers: The following people were elected officers of
the ASGRG Committee by acclamation (the mover and seconder are
shown in brackets):
President: David Wiltshire (Scott, Steele)
Treasurer: John Steele (McClelland, Scott)
Secretary: Malcolm Anderson (McClelland, Scott)
Officer: Ju Li (McClelland, Scott)
Officer: Susan Scott (Wiltshire, Steele)
8. Other business:
John Steele moved that the fee for life membership for retired members of
the ASGRG over the age of 65 be reduced to $125, and Ishwaree Neupane
seconded. The motion was approved.
The meeting closed at 6.20 pm with a vote of thanks for the outgoing
president, Susan Scott.
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6TH AUSTRALASIAN CONFERENCE ON GENERAL RELATIVITY AND GRAVITATION (ACGRG6)
University of Adelaide, February 2012
FIRST ANNOUNCEMENT
ACGRG6 is the sixth in a series of biennial conferences run by the ASGRG
with the aim of bringing together researchers from around the world to
discuss new findings in mathematical, theoretical, numerical and
experimental gravitation, to make contacts and consolidate ideas.
ACGRG6 will be held on the campus of the University of Adelaide, over a
three-day period in February 2012. The exact dates will be announced when
they have been finalised.
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7th BIENNIAL GENERAL MEETING OF THE ASGRG
The 2012 Biennial General Meeting of the ASGRG will be held in conjunction
with ACGRG6, at a date in February 2012 to be determined.
All ASGRG Executive Committee positions will be filled by election at the
BGM. The outgoing Executive Committee members are:
President - David Wiltshire
Treasurer - John Steele
Secretary - Malcolm Anderson
Officer - Susan Scott
Officer - Ju Li
Co-Opted committee members: Peter Veitch, Jesper Munch
Nominations will be called for as soon as the arrangements for ACGRG6 have
been finalised.
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20th CONGRESS OF THE AUSTRALIAN INSTITUTE OF PHYSICS
Sydney Convention Centre, 9-13 December 2012
FIRST ANNOUNCEMENT
The next AIP Congress is scheduled to be held at the Sydney Convention Centre
from 9 to 13 December 2012. It will coincide with celebrations of the 50th
anniversary of the AIP.
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MEMBERSHIP DETAILS ONLINE:
Due to requests from members, David Wiltshire has written some HTML
scripts which generate membership details online from our records. If you
click on
http://www.physics.adelaide.edu.au/ASGRG/members.html
you will find a members' list. Clicking on individual members gives their
current contact details. By following a further link private details of the
subscription status of any member will be sent to their registered email.
This feature should enable us to update our records more frequently in
response to members' input, and to allow members to keep track of their
subscriptions.
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SUBSCRIPTIONS:
The membership script programs are intended to be run automatically once
a year, at the end of July, to give members other than life members
details of their current subscription status.
The new version of the subscription form, at
http://www2.phys.canterbury.ac.nz/ASGRG/subsform.html
has been simplified so that it does not need to be updated each year.
Given that our annual fee is modest, members are encouraged to pay for
multiple years, and to fill in the years they are paying for. E.g., when
the July 2009 - June 2010 subscriptions are requested, if you wish to
pay for July 2010 - June 2011 at the same time, it may simplify matters.
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FORTHCOMING MEETINGS
September 12-16, 2011: Third Galileo-Xu Guangqi Meeting
"The Sun, the Stars, the Universe and General Relativity"
National Astronomical Observatories, Beijing, China
http://www.icranet.org/index.php?option=com_content&task=view&id=544
December 14-19, 2011: Seventh International Conference on Gravitation and Cosmology (ICGC 2011)
Goa, India
http://www.icts.res.in/program/details/211/
February 2012: Sixth Australasian Conference on General Relativity and Gravitation (ACGRG6)
University of Adelaide, Australia
July 1-7, 2012: Thirteenth Marcel Grossmann Meeting on General Relativity (MG13)
Stockholm, Sweden
http://www.icra.it/mg/mg13/
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MEMBERS' ABSTRACTS at gr-qc, December 2008 - June 2011
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 Los Alamos archives which
are not crosslinked 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.
The 179 papers listed here and in the LIGO section represent 1.9% of the
9524 papers posted or cross-linked to gr-qc between December 2008 and June
2011.
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arXiv:1002.3581
Quantum corrections to the entropy of charged rotating black holes
Authors: M. Akbar, K. Saifullah
(Submitted on 18 Feb 2010)
Hawking radiation from a black hole can be viewed as quantum tunneling of particles through the event horizon. Using this approach we provide a general framework for studying corrections to the entropy of black holes beyond semiclassical approximations. Applying the properties of exact differentials for three variables to the first law thermodynamics, we study charged rotating black holes and explicitly work out the corrections to entropy and horizon area for the Kerr-Newman and charged rotating BTZ black holes. It is shown that the results for other geometries like the Schwarzschild, Reissner-Nordstr\"{o}m and anti-de Sitter Schwarzschild spacetimes follow easily.
Journal reference: Eur. Phys. J. C Vol 67 (2010) 205
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arXiv:1002.3901
Quantum corrections to the entropy of Einstein-Maxwell dilaton-axion black holes
Authors: M. Akbar, K. Saifullah
(Submitted on 20 Feb 2010)
We study the corrections to the entropy of Einstein-Maxwell dilaton-axion black holes beyond semiclassical approximations. We consider the entropy of the black hole as a state variable and derive these corrections using the exactness criteria of the first law of thermodynamics. We note that from this general frame-work the entropy corrections for "simpler" black holes like Schwarzschild, Reissner-Nordstr\"{o}m and anti-de Sitter-Schwarzschild black holes follow easily. This procedure gives us the modified area law as well.
Journal reference: Gen. Relativ. Gravit. 43 (2011) 933
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arXiv:1005.1388
Exact differential and quantum corrections of entropy for axially symmetric black holes
Authors: M. Akbar, K. Saifullah
(Submitted on 9 May 2010)
Using the exactness criteria of entropy from the first law of black hole thermodynamics, we study quantum corrections for axially symmetric black holes.
Journal reference: Proc. 12th Marcel Grossmann Meeting on General Relativity, World Scientific, 2010
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arXiv:1005.3444
Generalized second law of thermodynamics for a phantom energy accreting BTZ black hole
Authors: Mubasher Jamil, M. Akbar
(Submitted on 19 May 2010 (v1), last revised 1 Jun 2010 (this version, v2))
In this paper, we have studied the accretion of phantom energy on a (2+1)-dimensional stationary Banados-Teitelboim-Zanelli (BTZ) black hole. It has already been shown by Babichev et al that for the accretion of phantom energy onto a Schwarzschild black hole, the mass of black hole would decrease and the rate of change of mass would be dependent on the mass of the black hole. However, in the case of (2+1)-dimensional BTZ black hole, the mass evolution due to phantom accretion is independent of the mass of the black hole and is dependent only on the pressure and density of the phantom energy. We also study the generalized second law of thermodynamics at the event horizon and construct a condition that puts an lower bound on the pressure of the phantom energy.
Journal reference: Gen.Rel.Grav.43:1061-1068,2011
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arXiv:1009.3749
Charged Rotating BTZ Black Hole and Thermodynamic Behavior of Field Equations at its Horizon
Authors: M. Akbar, Azad A. Siddiqui
(Submitted on 20 Sep 2010)
12 pages, 3 figures
In this paper, we study different cases of the charged rotating BTZ black hole with reference to their horizons. For the existence of these cases conditions on mass, charge and angular momentum of the black hole are obtained. It is also shown that the Einstein field equations for the charged rotating BTZ black hole at the horizon can be expressed as first law of thermodynamics, $dE=TdS+\Omega dJ+\Phi dq+P_{r}dA$.
Journal reference: Physics Letters B 656 (2007) 217-220
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arXiv:1011.5703
Dynamics and Thermodynamics of (2+1)-Dimensional Evolving Lorentzian Wormhole
Authors: M. Umar Farooq, M. Akbar, Mubasher Jamil
(Submitted on 26 Nov 2010)
20 pages, 4 figures
In this paper we study the relationship between the Einstein field equations for the (2+1)-dimensional evolving wormhole and the first law of thermodynamics. It has been shown that the Einstein field equations can be rewritten as a similar form of the first law of thermodynamics at the dynamical trapping horizon (as proposed by Hayward) for the dynamical spacetime which describes intrinsic thermal properties associated with the trapping horizon. For a particular choice of the shape and potential functions we are able to express field equations as a similar form of first law of thermodynamics $dE=-TdS+WdA$ at the trapping horizons. Here $E=\rho A$, $T=-\kappa /2\pi $, $S=4\pi \tilde{r}_{A}$, $W=(\rho -p)/2$%, and $A=\pi \tilde{r}_{A}^{2}$, are the total matter energy, horizon temperature, wormhole entropy, work density and volume of the evolving wormhole respectively.
Journal reference: AIP Conf. Proc. 1295 (2010) 176-190
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arXiv:1101.2722
Thermodynamic Geometry Of Charged Rotating BTZ Black Holes
Authors: M. Akbar, H. Quevedo, K. Saifullah, A. Sanchez, S. Taj
(Submitted on 14 Jan 2011)
We study the thermodynamics and the thermodynamic geometries of charged rotating BTZ (CR-BTZ) black holes in (2+1)-gravity. We investigate the thermodynamics of these systems within the context of the Weinhold and Ruppeiner thermodynamic geometries and the recently developed formalism of geometrothermodynamics (GTD). Considering the behavior of the heat capacity and the Hawking temperature, we show that Weinhold and Ruppeiner geometries cannot describe completely the thermodynamics of these black holes and of their limiting case of vanishing electric charge. In contrast, the Legendre invariance imposed on the metric in GTD allows one to describe the CR-BTZ black holes and their limiting cases in a consistent and invariant manner.
Journal reference: Phys.Rev.D83:084031,2011
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arXiv:0812.2523
Continuous self-similar evaporation of a rotating cosmic string loop
Authors: Malcolm Anderson
(Submitted on 13 Dec 2008)
80 pages, 13 figures
A solution of the linearized Einstein and Nambu-Goto equations is constructed which describes the evaporation of a certain type of rotating cosmic string - the Allen-Casper-Ottewill loop - under the action of its own self-gravity. The solution evaporates self-similarly, and radiates away all its mass-energy and momentum in a finite time. Furthermore, the corresponding weak-field metric can be matched to a remnant Minkowski spacetime at all points on the future light cone of the final evaporation point of the loop.
Journal reference: Class.Quant.Grav.26:025006,2009
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arXiv:0903.4943
Gravitational waveforms from the evaporating ACO cosmic string loop
Authors: Malcolm Anderson
(Submitted on 28 Mar 2009)
30 pages, 16 figures
he linearly polarized gravitational waveforms from a certain type of rotating, evaporating cosmic string - the Allen-Casper-Ottewill loop - are constructed and plotted over the lifetime of the loop. The formulas for the waveforms are simple and exact, and describe waves which attenuate self-similarly, with the amplitude and period of the waves falling off linearly with time.
Journal reference: Class.Quant.Grav.26:075018,2009
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arXiv:0907.3816
Comment on `The Newtonian force experienced by a point mass near a finite cylindrical source'
Authors: M Azreg-Aïnou
(Submitted on 22 Jul 2009)
2 pages
We compare the computation times and precisions of three expansions for the gravitational potential. The evaluation of the series by Selvaggi et al (2008 \textit{Class. Quantum Grav.} \textbf{25} 015013) is time-consuming to be applied to the gravitational constant ($G$) or STEP experiments.
Journal reference: Class.Quant.Grav.26:158001,2009
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arXiv:0912.1722
Selection criteria for two-parameter solutions to scalar-tensor gravity
Authors: Mustapha Azreg-Aïnou
(Submitted on 9 Dec 2009)
24 pages, 7 figures, 2 tables
We make a systematic investigation of the generic properties of static, spherically symmetric, asymptotically flat solutions to the field equations describing gravity minimally coupled to a nonlinear self-gravitating real scalar field. Seven corollaries and a theorem on selection criteria for two- and one-parametric solutions are proven and conditions for obtaining particle-like solution, black holes or naked singularities are derived. A series of exact solutions in closed forms describing different black holes, naked singularities and particle-like solutions are provided.
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Developed Adomian method for quadratic Kaluza-Klein relativity
Authors: Mustapha Azreg-Aïnou
(Submitted on 16 Dec 2009)
17 pages
We develop and modify the Adomian decomposition method (ADecM) to work for a new type of nonlinear matrix differential equations (MDE's) which arise in general relativity (GR) and possibly in other applications. The approach consists in modifying both the ADecM linear operator with highest order derivative and ADecM polynomials. We specialize in the case of a 4$\times$4 nonlinear MDE along with a scalar one describing stationary cylindrically symmetric metrics in quadratic 5-dimensional GR, derive some of their properties using ADecM and construct the \textit{most general unique power series solutions}. However, because of the constraint imposed on the MDE by the scalar one, the series solutions terminate in closed forms exhausting all possible solutions.
Journal reference: Class.Quant.Grav.27:015012,2010
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arXiv:1102.4093
Phantom Black Holes and Sigma Models
Authors: Mustapha Azreg-Aïnou, Gérard Clément, Júlio C. Fabris, Manuel E. Rodrigues
(Submitted on 20 Feb 2011)
19 pages
We construct static multicenter solutions of phantom Einstein-Maxwell-dilaton theory from null geodesics of the target space, leading to regular black holes without spatial symmetry for certain discrete values of the dilaton coupling constant. We also discuss the three-dimensional gravitating sigma models obtained by reduction of phantom Einstein-Maxwell, phantom Kaluza-Klein and phantom Einstein-Maxwell-dilaton-axion theories. In each case, we generate by group transformations phantom charged black hole solutions from a neutral seed.
Journal reference: Phys.Rev.D83:124001,2011
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arXiv:1106.0970
Comment on `Spinning loop black holes' [arXiv:1006.0232]
Authors: Mustapha Azreg-Aïnou
(Submitted on 6 Jun 2011)
2 pages, 1 figure
We review the derivations and conclusions made in Caravelli and Modesto (2010 \textit{Class. Quantum Grav.} \textbf{27} 245022, arXiv:1006.0232) and show that most of the analysis performed there is not valid.
Journal reference: Class. Quantum Grav. 28 (2011) 148001
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arXiv:0907.3975
Static Spherically Symmetric Solutions of the SO(5) Einstein Yang-Mills Equations
Authors: Robert A. Bartnik, Mark Fisher, Todd A. Oliynyk
(Submitted on 23 Jul 2009)
11 pages, 5 figures, 1 table
Globally regular (ie. asymptotically flat and regular interior), spherically symmetric and localised ("particle-like") solutions of the coupled Einstein Yang-Mills (EYM) equations with gauge group SU(2) have been known for more than 20 years, yet their properties are still not well understood. Spherically symmetric Yang--Mills fields are classified by a choice of isotropy generator and SO(5) is distinguished as the simplest model with a \emph{non-Abelian} residual (little) group, $SU(2)\times U(1)$, and which admits globally regular particle-like solutions. We exhibit an algebraic gauge condition which normalises the residual gauge freedom to a finite number of discrete symmetries. This generalises the well-known reduction to the real magnetic potential $w(r,t)$ in the original SU(2) YM model. Reformulating using gauge invariant polynomials dramatically simplifies the system and makes numerical search techniques
feasible. We find three families of embedded SU(2) EYM equations within the SO(5) system, one of which was first detected only within the gauge-invariant polynomial reduced system. Numerical solutions representing mixtures of the three SU(2) sub-systems are found, classified by a pair of positive integers.
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arXiv:0904.0773
An emergent universe supported by a nonlinear sigma model
Authors: A. Beesham, S. V. Chervon, S. D. Maharaj
(Submitted on 5 Apr 2009)
10 pages
We suggest the use of a nonlinear sigma model as the source which supports an emergent universe. The two-component nonlinear sigma model is considered as the simplest model containing inflaton and auxiliary chiral fields.
Journal reference: Class.Quant.Grav.26:075017,2009
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arXiv:0906.4175
Application of Graphics Processing Units to Search Pipeline for Gravitational Waves from Coalescing Binaries of Compact Objects
Authors: Shin Kee Chung, Linqing Wen, David Blair, Kipp Cannon, Amitava Datta
(Submitted on 23 Jun 2009 (v1), last revised 17 May 2010 (this version, v2))
15 pages, 7 figures
We report a novel application of graphics processing units (GPUs) for the purpose of accelerating the search pipelines for gravitational waves from coalescing binaries of compact objects. A speed-up of 16 fold has been achieved compared with a single central processing unit (CPU). We show that substantial improvements are possible and discuss the reduction in CPU count required for the detection of inspiral sources afforded by the use of GPUs.
Journal reference: Class.Quant.Grav.27:135009,2010
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arXiv:1007.4289
Using temporal distributions of transient events to characterize cosmological source populations
Authors: E. Howell, D. Coward, R. Burman, D. Blair
(Submitted on 25 Jul 2010)
The brightest events in a time series of cosmological transients obey an observation time dependence which is often overlooked. This dependence can be exploited to probe the global properties of electromagnetic and gravitational wave transients (Howell et al. 2007a, Coward & Burman 2005). We describe a new relation based on a peak flux--observation time distribution and show that it is invariant to the luminosity distribution of the sources (Howell et al. 2007b). Applying this relation, in combination with a new data analysis filter, to \emph{Swift} gamma-ray burst data, we demonstrate that it can constrain their rate density.
Journal reference: AIP (2010),1246,203
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arXiv:1008.0472
Observational upper limits on the gravitational wave production of core collapse supernovae
Authors: Xing-Jiang Zhu, Eric Howell, David Blair
(Submitted on 3 Aug 2010 (v1), last revised 4 Oct 2010 (this version, v3))
The upper limit on the energy density of a stochastic gravitational wave (GW) background obtained from the two-year science run (S5) of the Laser Interferometer Gravitational-wave Observatory (LIGO) is used to constrain the average GW production of core collapse supernovae (ccSNe). We assume that the ccSNe rate tracks the star formation history of the universe and show that the stochastic background energy density depends only weakly on the assumed average source spectrum. Using the ccSNe rate for $z\leq10$, we scale the generic source spectrum to obtain an observation-based upper limit on the average GW emission. We show that the mean energy emitted in GWs can be constrained within $< (0.49-1.98){1mm} M_{\odot} c^{2}$ depending on the average source spectrum. While these results are higher than the total available gravitational energy in a core collapse event, second and third generation GW detectors will enable
tighter constraints to be set on the GW emission from such systems.
Journal reference: Mon.Not.Roy.Astron.Soc.409:L132-L136,2010
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arXiv:1104.3565
Stochastic Gravitational Wave Background from Coalescing Binary Black Holes
Authors: Xing-Jiang Zhu, Eric Howell, Tania Regimbau, David Blair, Zong-Hong Zhu
(Submitted on 18 Apr 2011 (v1), last revised 8 Jul 2011 (this version, v3))
22 pages, 5 figures, 2 tables, Accepted for publication by ApJ
We estimate the stochastic gravitational wave (GW) background signal from the field population of coalescing binary stellar mass black holes (BHs) throughout the Universe. This study is motivated by recent observations of BH-Wolf-Rayet star systems and by new estimates in the metallicity abundances of star forming galaxies that imply BH-BH systems are more common than previously assumed. Using recent analytical results of the inspiral-merger-ringdown waveforms for coalescing binary BH systems, we estimate the resulting stochastic GW background signal. Assuming average quantities for the single source energy emissions, we explore the parameter space of chirp mass and local rate density required for detection by advanced and third generation interferometric GW detectors. For an average chirp mass of 8.7$M_{\odot}$, we find that detection through 3 years of cross-correlation by two advanced detectors will require a rate density, $r_0
\geq 0.5 \rm{Mpc}^{-3} \rm{Myr}^{-1}$. Combining data from multiple pairs of detectors can reduce this limit by up to 40%. Investigating the full parameter space we find that detection could be achieved at rates $r_0 \sim 0.1 \rm{Mpc}^{-3} \rm{Myr}^{-1}$ for populations of coalescing binary BH systems with average chirp masses of $\sim 15M_{\odot}$ which are predicted by recent studies of BH-Wolf-Rayet star systems. While this scenario is at the high end of theoretical estimates, cross-correlation of data by two Einstein Telescopes could detect this signal under the condition $r_0 \geq 10^{-3} \rm{Mpc}^{-3} \rm{Myr}^{-1}$. Such a signal could potentially mask a primordial GW background signal of dimensionless energy density, $\Omega_{\rm{GW}}\sim 10^{-10}$, around the (1--500) Hz frequency range.
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arXiv:0903.2085
A brief introduction to Cadabra: a tool for tensor computations in General Relativity
Authors: Leo Brewin
(Submitted on 12 Mar 2009)
15 pages
Cadabra is a powerful computer program for the manipulation of tensor equations. It was designed for use in high energy physics but its rich structure and ease of use lends itself well to the routine computations required in General Relativity. Here we will present a series of simple examples showing how Cadabra may be used, including verifying that the Levi-Civita connection is a metric connection and a derivation of the Gauss equation between induced and ambient curvatures.
Journal reference: Comput.Phys.Commun.181:489-498,2010
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arXiv:0903.2087
Riemann Normal Coordinate expansions using Cadabra
Authors: Leo Brewin
(Submitted on 12 Mar 2009)
27 pages
We present the results of using the computer algebra program Cadabra to develop Riemann normal coordinate expansions of the metric and other geometrical quantities, in particular the geodesic arc-length. All of the results are given to sixth-order in the curvature tensor.
Journal reference: Class.Quant.Grav.26:175017,2009
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arXiv:0903.5365
Deriving the ADM 3+1 evolution equations from the second variation of arc length
Authors: Leo Brewin
(Submitted on 31 Mar 2009)
We will show that the ADM 3+1 evolution equations, for a zero shift vector, arise naturally from the equations for the second variation of arc-length.
Journal reference: Phys.Rev.D80:084030,2009
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arXiv:0903.5367
A Smooth Lattice construction of the Oppenheimer-Snyder spacetime
Authors: Leo Brewin, Jules Kajtar
(Submitted on 31 Mar 2009)
60 pages, 28 figures
We present test results for the smooth lattice method using an Oppenheimer-Snyder spacetime. The results are in excellent agreement with theory and numerical results from other authors.
Journal reference: Phys.Rev.D80:104004,2009
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arXiv:1011.1885
Fast algorithms for computing defects and their derivatives in the Regge calculus
Authors: Leo Brewin
(Submitted on 8 Nov 2010)
38 pages, 10 figures
Any practical attempt to solve the Regge equations, these being a large system of non-linear algebraic equations, will almost certainly employ a Newton-Raphson like scheme. In such cases it is essential that efficient algorithms be used when computing the defect angles and their derivatives with respect to the leg-lengths. The purpose of this paper is to present details of such an algorithm.
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arXiv:1101.3171
An Einstein-Bianchi system for Smooth Lattice General Relativity. I. The Schwarzschild spacetime
Authors: Leo Brewin
(Submitted on 17 Jan 2011 (v1), last revised 7 Apr 2011 (this version, v2))
The second Bianchi identity can be recast as an evolution equation for the Riemann curvatures. Here we will report on such a system for a vacuum static spherically symmetric spacetime. This is the first of two papers. In the following paper we will extend the ideas developed here to general vacuum spacetimes. In this paper we will demonstrate our ideas on a Schwarzschild spacetime and give detailed numerical results. For suitable choices of lapse function we find that the system gives excellent results with long term stability.
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arXiv:1104.1356
An Einstein-Bianchi system for Smooth Lattice General Relativity. II. 3+1 vacuum spacetimes
Authors: Leo Brewin
(Submitted on 7 Apr 2011)
We will present a complete set of equations, in the form of an Einstein-Bianchi system, that describe the evolution of generic smooth lattices in spacetime. All 20 independent Riemann curvatures will be evolved in parallel with the leg-lengths of the lattice. We will show that the evolution equations for the curvatures forms a hyperbolic system and that the associated constraints are preserved. This work is a generalisation of our previous paper arXiv:1101.3171 on the Einstein-Bianchi system for the Schwarzschild spacetime to general 3+1 vacuum spacetimes.
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arXiv:0812.1590
Characterizing the Gravitational Wave Signature from Cosmic String Cusps
Authors: Joey Shapiro Key, Neil J. Cornish
(Submitted on 8 Dec 2008)
10 pages, 10 figures
Cosmic strings are predicted to form kinks and cusps that travel along the string at close to the speed of light. These disturbances are radiated away as highly beamed gravitational waves that produce a burst like pulse as the cone of emission sweeps past an observer. Gravitational wave detectors such as the Laser Interferometer Space Antenna (LISA) and the Laser Interferometer Gravitational wave Observatory (LIGO) will be capable of detecting these bursts for a wide class of string models. Such a detection would illuminate the fields of string theory, cosmology, and relativity. Here we develop template based Markov Chain Monte Carlo (MCMC) techniques that can efficiently detect and characterize the signals from cosmic string cusps. We estimate how well the signal parameters can be recovered by the advanced LIGO-Virgo network and the LISA detector using a combination of MCMC and Fisher matrix techniques. We also consider
joint detections by the ground and space based instruments. We show that a parallel tempered MCMC approach can detect and characterize the signals from cosmic string cusps, and we demonstrate the utility of this approach on simulated data from the third round of Mock LISA Data Challenges (MLDCs).
Journal reference: Phys.Rev.D79:043014,2009
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arXiv:0902.0368
A Bayesian Approach to the Detection Problem in Gravitational Wave Astronomy
Authors: Tyson B. Littenberg, Neil J. Cornish
(Submitted on 2 Feb 2009 (v1), last revised 16 Jul 2009 (this version, v2))
19 pages, 12 figures
The analysis of data from gravitational wave detectors can be divided into three phases: search, characterization, and evaluation. The evaluation of the detection - determining whether a candidate event is astrophysical in origin or some artifact created by instrument noise - is a crucial step in the analysis. The on-going analyses of data from ground based detectors employ a frequentist approach to the detection problem. A detection statistic is chosen, for which background levels and detection efficiencies are estimated from Monte Carlo studies. This approach frames the detection problem in terms of an infinite collection of trials, with the actual measurement corresponding to some realization of this hypothetical set. Here we explore an alternative, Bayesian approach to the detection problem, that considers prior information and the actual data in hand. Our particular focus is on the computational techniques used to implement
the Bayesian analysis. We find that the Parallel Tempered Markov Chain Monte Carlo (PTMCMC) algorithm is able to address all three phases of the anaylsis in a coherent framework. The signals are found by locating the posterior modes, the model parameters are characterized by mapping out the joint posterior distribution, and finally, the model evidence is computed by thermodynamic integration. As a demonstration, we consider the detection problem of selecting between models describing the data as instrument noise, or instrument noise plus the signal from a single compact galactic binary. The evidence ratios, or Bayes factors, computed by the PTMCMC algorithm are found to be in close agreement with those computed using a Reversible Jump Markov Chain Monte Carlo algorithm.
Journal reference: Phys.Rev.D80:063007,2009
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arXiv:0910.4372
Alternative derivation of the response of interferometric gravitational wave detectors
Authors: Neil J. Cornish
(Submitted on 22 Oct 2009)
2 pages
It has recently been pointed out by Finn that the long-standing derivation of the response of an interferometric gravitational wave detector contains several errors. Here I point out that a contemporaneous derivation of the gravitational wave response for spacecraft doppler tracking and pulsar timing avoids these pitfalls, and when adapted to describe interferometers, recovers a simplified version of Finn's derivation. This simplified derivation may be useful for pedagogical purposes.
Journal reference: Phys.Rev.D80:087101,2009
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arXiv:1002.1291
Discriminating between a Stochastic Gravitational Wave Background and Instrument Noise
Authors: Matthew R. Adams, Neil J. Cornish
(Submitted on 5 Feb 2010)
10 Pages, 10 Figures
The detection of a stochastic background of gravitational waves could significantly impact our understanding of the physical processes that shaped the early Universe. The challenge lies in separating the cosmological signal from other stochastic processes such as instrument noise and astrophysical foregrounds. One approach is to build two or more detectors and cross correlate their output, thereby enhancing the common gravitational wave signal relative to the uncorrelated instrument noise. When only one detector is available, as will likely be the case with the Laser Interferometer Space Antenna (LISA), alternative analysis techniques must be developed. Here we show that models of the noise and signal transfer functions can be used to tease apart the gravitational and instrument noise contributions. We discuss the role of gravitational wave insensitive "null channels" formed from particular
combinations of the time delay interferometry, and derive a new combination that maintains this insensitivity for unequal arm length detectors. We show that, in the absence of astrophysical foregrounds, LISA could detect signals with energy densities as low as $\Omega_{\rm gw} = 6 \times 10^{-13}$ with just one month of data. We describe an end-to-end Bayesian analysis pipeline that is able to search for, characterize and assign confidence levels for the detection of a stochastic gravitational wave background, and demonstrate the effectiveness of this approach using simulated data from the third round of Mock LISA Data Challenges.
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arXiv:1004.5322
Computing waveforms for spinning compact binaries in quasi-eccentric orbits
Authors: Neil J. Cornish, Joey Shapiro Key
(Submitted on 29 Apr 2010 (v1), last revised 9 Jul 2010 (this version, v4))
11 pages
Several scenarios have been proposed in which the orbits of binary black holes enter the band of a gravitational wave detector with significant eccentricity. To avoid missing these signals or biasing parameter estimation it is important that we consider waveform models that account for eccentricity. The ingredients needed to compute post-Newtonian (PN) waveforms produced by spinning black holes inspiralling on quasi-eccentric orbits have been available for almost two decades at 2 PN order, and this work has recently been extended to 2.5 PN order. However, the computational cost of directly implementing these waveforms is high, requiring many steps per orbit to evolve the system of coupled differential equations. Here we employ the standard techniques of a separation of timescales and a generalized Keplerian parameterization of the orbits to produce efficient waveforms describing spinning black hole binaries with
arbitrary masses and spins on quasi-eccentric orbits to 1.5 PN order. We separate the fast orbital timescale from the slow spin-orbit precession timescale by solving for the orbital motion in a non-interial frame of reference that follows the orbital precession. We outline a scheme for extending our approach to higher post-Newtonian order.
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arXiv:1006.3759
Characterizing Spinning Black Hole Binaries in Eccentric Orbits with LISA
Authors: Joey Shapiro Key, Neil J. Cornish
(Submitted on 18 Jun 2010 (v1), last revised 12 Feb 2011 (this version, v3))
11 pages, 13 figures
The Laser Interferometer Space Antenna (LISA) is designed to detect gravitational wave signals from astrophysical sources, including those from coalescing binary systems of compact objects such as black holes. Colliding galaxies have central black holes that sink to the center of the merged galaxy and begin to orbit one another and emit gravitational waves. Some galaxy evolution models predict that the binary black hole system will enter the LISA band with significant orbital eccentricity, while other models suggest that the orbits will already have circularized. Using a full seventeen parameter waveform model that includes the effects of orbital eccentricity, spin precession and higher harmonics, we investigate how well the source parameters can be inferred from simulated LISA data. Defining the reference eccentricity as the value one year before merger, we find that for typical LISA sources, it will be possible to measure the
eccentricity to an accuracy of parts in a thousand. The accuracy with which the eccentricity can be measured depends only very weakly on the eccentricity, making it possible to distinguish circular orbits from those with very small eccentricities. LISA measurements of the orbital eccentricity can help constraints theories of galaxy mergers in the early universe. Failing to account for the eccentricity in the waveform modeling can lead to a loss of signal power and bias the estimation of parameters such as the black hole masses and spins.
Journal reference: Phys.Rev.D83:083001,2011
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arXiv:1007.4820
Fast Fisher Matrices and Lazy Likelihoods
Authors: Neil J. Cornish
(Submitted on 27 Jul 2010 (v1), last revised 11 Aug 2010 (this version, v2))
5 pages, 1 figure
Theoretical studies in gravitational wave astronomy often require the calculation of Fisher Information Matrices and Likelihood functions, which in a direct approach entail the costly step of computing gravitational waveforms. Here I describe an alternative technique that sidesteps the need to compute full waveforms, resulting in significant computational savings. I describe how related techniques can be used to speed up Bayesian inference applied to real gravitational wave data.
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arXiv:1008.1577
Separating Gravitational Wave Signals from Instrument Artifacts
Authors: Tyson B. Littenberg, Neil J. Cornish
(Submitted on 9 Aug 2010)
21 pages, 18 figures
Central to the gravitational wave detection problem is the challenge of separating features in the data produced by astrophysical sources from features produced by the detector. Matched filtering provides an optimal solution for Gaussian noise, but in practice, transient noise excursions or ``glitches'' complicate the analysis. Detector diagnostics and coincidence tests can be used to veto many glitches which may otherwise be misinterpreted as gravitational wave signals. The glitches that remain can lead to long tails in the matched filter search statistics and drive up the detection threshold. Here we describe a Bayesian approach that incorporates a more realistic model for the instrument noise allowing for fluctuating noise levels that vary independently across frequency bands, and deterministic ''glitch fitting'' using wavelets as ''glitch templates'', the number of which is determined by a trans-dimensional
Markov chain Monte Carlo algorithm. We demonstrate the method's effectiveness on simulated data containing low amplitude gravitational wave signals from inspiraling binary black hole systems, and simulated non-stationary and non-Gaussian noise comprised of a Gaussian component with the standard LIGO/Virgo spectrum, and injected glitches of various amplitude, prevalence, and variety. Glitch fitting allows us to detect significantly weaker signals than standard techniques.
Journal reference: Phys.Rev.D82:103007,2010
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arXiv:1008.1782
Pulsar Timing Array Observations of Massive Black Hole Binaries
Authors: Vincent Corbin, Neil J. Cornish
(Submitted on 10 Aug 2010 (v1), last revised 16 Aug 2010 (this version, v2))
10 pages, 9 figures
Pulsar timing is a promising technique for detecting low frequency sources of gravitational waves. Historically the focus has been on the detection of diffuse stochastic backgrounds, such as those formed from the superposition of weak signals from a population of binary black holes. More recently, attention has turned to members of the binary population that are nearer and brighter, which stand out from the crowd and can be individually resolved. Here we show that the timing data from an array of pulsars can be used to recover the physical parameters describing an individual black hole binary to good accuracy, even for moderately strong signals. A novel aspect of our analysis is that we include the distance to each pulsar as a search parameter, which allows us to utilize the full gravitational wave signal. This doubles the signal power, improves the sky location determination by an order of magnitude, and allows us to extract
the mass and the distance to the black hole binary.
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arXiv:1101.3591
Measuring parameters of massive black hole binaries with partially aligned spins
Authors: Ryan N. Lang, Scott A. Hughes, Neil J. Cornish
(Submitted on 19 Jan 2011)
19 pages, 16 figures, submitted to PRD
The future space-based gravitational wave detector LISA will be able to measure parameters of coalescing massive black hole binaries, often to extremely high accuracy. Previous work has demonstrated that the black hole spins can have a strong impact on the accuracy of parameter measurement. Relativistic spin-induced precession modulates the waveform in a manner which can break degeneracies between parameters, in principle significantly improving how well they are measured. Recent studies have indicated, however, that spin precession may be weak for an important subset of astrophysical binary black holes: those in which the spins are aligned due to interactions with gas. In this paper, we examine how well a binary's parameters can be measured when its spins are partially aligned and compare results using waveforms that include higher post-Newtonian harmonics to those that are truncated at leading quadrupole
order. We find that the weakened precession can substantially degrade parameter estimation, particularly for the "extrinsic" parameters sky position and distance. Absent higher harmonics, LISA typically localizes the sky position of a nearly aligned binary about an order of magnitude less accurately than one for which the spin orientations are random. Our knowledge of a source's sky position will thus be worst for the gas-rich systems which are most likely to produce electromagnetic counterparts. Fortunately, higher harmonics of the waveform can make up for this degradation. By including harmonics beyond the quadrupole in our waveform model, we find that the accuracy with which most of the binary's parameters are measured can be substantially improved. In some cases, the improvement is such that they are measured almost as well as when the binary spins are randomly aligned.
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arXiv:1105.2088
Gravitational Wave Tests of General Relativity with the Parameterized Post-Einsteinian Framework
Authors: Neil Cornish, Laura Sampson, Nico Yunes, Frans Pretorius
(Submitted on 11 May 2011)
17 pages, 17 figures
Gravitational wave astronomy has tremendous potential for studying extreme astrophysical phenomena and exploring fundamental physics. The waves produced by binary black hole mergers will provide a pristine environment in which to study strong field, dynamical gravity. Extracting detailed information about these systems requires accurate theoretical models of the gravitational wave signals. If gravity is not described by General Relativity, analyses that are based on waveforms derived from Einstein's field equations could result in parameter biases and a loss of detection efficiency. A new class of "parameterized post-Einsteinian" (ppE) waveforms has been proposed to cover this eventuality. Here we apply the ppE approach to simulated data from a network of advanced ground based interferometers (aLIGO/aVirgo) and from a future spaced based interferometer (LISA). Bayesian inference and model selection are used to investigate
parameter biases, and to determine the level at which departures from general relativity can be detected. We find that in some cases the parameter biases from assuming the wrong theory can be severe. We also find that gravitational wave observations will beat the existing bounds on deviations from general relativity derived from the orbital decay of binary pulsars by a large margin across a wide swath of parameter space.
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arXiv:0907.0696
The Effect of Negative-Energy Shells on the Schwarzschild Black Hole
Authors: Jeffrey S Hazboun, Tevian Dray
(Submitted on 3 Jul 2009)
12 pages, 10 figures
We construct Penrose diagrams for Schwarzschild spacetimes joined by massless shells of matter, in the process correcting minor flaws in the similar diagrams drawn by Dray and 't Hooft, and confirming their result that such shells generate a horizon shift. We then consider shells with negative energy density, showing that the horizon shift in this case allows for travel between the heretofore causally separated exterior regions of the Schwarzschild geometry. These drawing techniques are then used to investigate the properties of successive shells, joining multiple Schwarzschild regions. Again, the presence of negative-energy shells leads to a causal connection between the exterior regions, even in (some) cases with two successive shells of equal but opposite total energy.
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arXiv:0907.5470
Tensor Generalizations of Affine Symmetry Vectors
Authors: Samuel A. Cook, Tevian Dray
(Submitted on 31 Jul 2009 (v1), last revised 14 Oct 2009 (this version, v2))
11 pages
A definition is suggested for affine symmetry tensors, which generalize the notion of affine vectors in the same way that (conformal) Killing tensors generalize (conformal) Killing vectors. An identity for these tensors is proved, which gives the second derivative of the tensor in terms of the curvature tensor, generalizing a well-known identity for affine vectors. Additionally, the definition leads to a good definition of homothetic tensors. The inclusion relations between these types of tensors are exhibited. The relationship between affine symmetry tensors and solutions to the equation of geodesic deviation is clarified, again extending known results about Killing tensors.
Journal reference: J.Math.Phys.50:122506,2009
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arXiv:1001.1252
On the Dynamics of Bianchi IX cosmological models
Authors: Hossein Farajollahi, Arvin Ravanpak
(Submitted on 8 Jan 2010)
11 pages, 1 figure
A cosmological description of the universe is proposed in the context of Hamiltonian formulation of a Bianchi IX cosmology minimally coupled to a massless scalar field. The classical and quantum results are studied with special attention to the case of closed Friedmann-Robertson-Walker model.
Journal reference: Int J Theor Phy, 48, 12, 3345-3352, 2009
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arXiv:1001.1255
Generalized Brans-Dicke cosmology in the presence of matter and dark energy
Authors: Hossein Farajollahi, Narges Mohamadi
(Submitted on 8 Jan 2010 (v1), last revised 8 Jun 2011 (this version, v2))
9 pages
We study the Generalized Brans-Dicke cosmology in the presence of matter and dark energy. Of particular interest for a constant Brans-Dicke parameter, the de Sitter space has also been investigated.
Journal reference: Int.J.Theor.Phys.49:72-78,2010
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arXiv:1004.3508
Cosmic Dynamics in the Chameleon Cosmology
Authors: H. Farajollahi, A. Salehi
(Submitted on 20 Apr 2010 (v1), last revised 8 Jun 2011 (this version, v2))
16 pages, 9 figures
We study in this paper chameleon cosmology applied to Friedmann-Robertson-Walker space, which gives rise to the equation of state (EoS) parameter larger than -1 in the past and less than -1 today, satisfying current observations. We also study cosmological constraints on the model using the time evolution of the cosmological redshift of distant sources which directly probes the expansion history of the universe. Due to the evolution of the universe's expansion rate, the model independent Cosmological Redshift Drift (CRD)test is expected to experience a small, systematic drift as a function of time. The model is supported by the observational data obtained from the test.
Journal reference: Int.J.Mod.Phys.D19:621-633,2010
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arXiv:1004.3512
Bouncing Universe and phantom crossing in Modified Gravity and its reconstruction
Authors: H. Farajollahi, F. Milani
(Submitted on 20 Apr 2010 (v1), last revised 8 Jun 2011 (this version, v2))
18 pages, 10 figures
In this paper we consider FRW cosmology in modified gravity which contain arbitrary functions $f(\phi)$. It is shown that the bouncing solution appears in the model whereas the equation of state (EoS) parameter crosses the phantom divider. The reconstruction of the model is also investigated with the aim to reconstruct the arbitrary functions and variables of the model.
Journal reference: Mod.Phys.Lett.A25:2349-2362,2010
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arXiv:1005.0062
Interacting Cosmic Fluids in Brans-Dicke Cosmology
Authors: H.Farajollahi, N. Mohamadi, H. Amiri
(Submitted on 1 May 2010 (v1), last revised 8 Jun 2011 (this version, v2))
13 pages, 8 figures
We provide a detailed description for power-law scaling FRW cosmological models in Brans-Dicke theory dominated by two interacting fluid components during the expansion of the universe.
Journal reference: Mod. Phys. Lett. A, 25, No. 30 (2010) 2579-2589
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arXiv:1005.2026
Cosmic Dynamics in $F(R,/phi)$ Gravity
Authors: H. Farajollahi, M. Setare, F. Milani, F. Tayebi
(Submitted on 12 May 2010 (v1), last revised 8 Jun 2011 (this version, v3))
15 pages, 12 figures
In this paper we consider FRW cosmology in $F(R,\phi)$ gravity. It is shown that in particular cases the bouncing behavior may appears in the model whereas the equation of state (EoS) parameter may crosses the phantom divider. For the dynamical universe, quantitatively we also find parameters in the model which satisfies two independent tests:the model independent Cosmological Redshift Drift (CRD) test and the type Ia supernova luminosity distances.
Journal reference: Gen.Rel.Grav.43:1657-1669,2011
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arXiv:1005.3140
A 5D noncompact Kaluza -Klein cosmology in the presence of Null perfect fluid
Authors: H. Farajollahi, H. Amiri
(Submitted on 18 May 2010 (v1), last revised 8 Jun 2011 (this version, v2))
9 pages
For the description of the early inflation, and acceleration expansion of the Universe, compatible with observational data, the 5D noncompact Kaluza--Klein cosmology is investigated. It is proposed that the 5D space is filled with a null perfect fluid, resulting a perfect fluid in 4D universe, plus one along the fifth dimension. By analyzing the reduced field equations for flat FRW model, we show the early inflationary behavior and current acceleration of the universe.
Journal reference: Int.J.Mod.Phys.D19:1823-1830,2010
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arXiv:1008.0910
On Dynamics of Brans--Dicke Theory of Gravitation
Authors: Hossein Farajollahi, Mehrdad Farhoudi, Hossein Shojaie
(Submitted on 5 Aug 2010 (v1), last revised 8 Jun 2011 (this version, v2))
15 pages
We study longstanding problem of cosmological clock in the context of Brans-Dicke theory of gravitation. We present the Hamiltonian formulation of the theory for a class of spatially homogenous cosmological models. Then, we show that formulation of the Brans-Dicke theory in the Einstein frame allows how an identification of an appropriate cosmological time variable, as a function of the scalar field in the theory, can be emerged in quantum cosmology. The classical and quantum results are applied to the Friedmann-Robertson-Walker cosmological models.
Journal reference: Int.J.Theor.Phys.49:2558-2568,2010
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arXiv:1009.5059
Chameleonic Generalized Brans--Dicke model and late-time acceleration
Authors: H.Farajollahi, M.Farhoudi, A.Salehi, H.Shojaie
(Submitted on 26 Sep 2010)
16 pages, 12 figures
In this paper we consider Chameleonic Generalized Brans--Dicke Cosmology in the framework of FRW universes. The bouncing solution and phantom crossing is investigated for the model. Two independent cosmological tests: Cosmological Redshift Drift (CRD) and distance modulus are applied to test the model with the observation.
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arXiv:1010.3589
Attractors, Statefinders and Observational Measurement for Chameleonic Brans--Dicke Cosmology
Authors: Hossein Farajollahi, Amin Salehi
(Submitted on 18 Oct 2010 (v1), last revised 8 Jun 2011 (this version, v4))
28 pages, 38 figures
We investigate chameleonic Brans--Dicke model applied to the FRW universes. A framework to study stability and attractor solutions in the phase space is developed for the model. We show that depending on the matter field and stability conditions, it is possible to realize phantom-like behavior without introducing phantom filed in the model while the stability is fulfilled and phantom crossing occurs. The statefinder parameters to the model for different kinds of matter interacting with the chameleon scalar field are studied. We also compare our model with present day observations.
Journal reference: JCAP 1011:006,2010
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Xiv:1103.3553
Stability analysis in Modified Non-Local Gravity
Authors: H. Farajollahi, F. Milani
(Submitted on 18 Mar 2011)
12 pages, 4 figures
In this paper we consider FRW cosmology in modified non-local gravity. The stability analysis shows that there is only one stable critical point for the model and the universe undergoes a quintessence dominated era.
Journal reference: Int. J. Theor. Phys. 50, 6, 1953-1961, 2011
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arXiv:1103.3554
The universe dynamics in the tachyon cosmology with non-minimal coupling to matter
Authors: H. Farajollahi, A. Ravanpak, G. F. Fadakar
(Submitted on 18 Mar 2011 (v1), last revised 8 Jun 2011 (this version, v2))
14 pages, 11 figures
Recently, the tachyon cosmology has been represented as dark energy model to support the current acceleration of the universe without phantom crossing. In this paper, we study the dynamics of the tachyon cosmology in which the field plays the role of tachyon field and also non--minimally coupled to the matter lagrangian. The model shows current universe acceleration and also phantom crossing in the future. Two cosmological tests are also performed to validate the model; the difference in the distance modulus and the model independent Cosmological Redshift Drift (CRD) test.
Journal reference: Mod. Phys. Lett. A, Vol. 26, No. 15 (2011) pp. 1125-1135
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arXiv:1105.4045
Stability Analysis in Tachyonic Potential Chameleon cosmology
Authors: H. Farajollahi, A. Salehi, F. Tayebi, A. Ravanpak
(Submitted on 20 May 2011 (v1), last revised 9 Jun 2011 (this version, v2))
20 pages, 13 figures
We study general properties of attractors for tachyonic potential chameleon scalar-field model which possess cosmological scaling solutions. An analytic formulation is given to obtain fixed points with a discussion on their stability. The model predicts a dynamical equation of state parameter with phantom crossing behavior for an accelerating universe. We constrain the parameters of the model by best fitting with the recent data-sets from supernovae and simulated data points for redshift drift experiment generated by Monte Carlo simulations.
Journal reference: JCAP 05(2011)017
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arXiv:1106.0091
A new approach in stability analysis: case study: tachyon cosmology with non-minimally coupled scalar field-matter
Authors: H. Farajollahi, A. Salehi
(Submitted on 1 Jun 2011 (v1), last revised 8 Jun 2011 (this version, v2))
21 pages, 30 figures; accepted for publication in Phys. Rev. D
Abstract: We study the general properties of attractors in a cosmological model with tachyonic potential and a scalar field non-minimally coupled to matter. A general analytic formulation is given to derive fixed points with a discussion on their stability. We also check the consistency of the model by fitting it to the supernovae type Ia data.
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arXiv:1106.1764
Entropy and statefinder diagnosis in chameleon cosmology
Authors: H. Farajollahi, A. Salehi, F. Tayebi
(Submitted on 9 Jun 2011)
11 pages, 5 figures. will be published in Astrophys. Space Sci
In this paper, the generalized second law (GSL) of thermodynamics and entropy is revisited in the context of cosmological models with bouncing behavior such as chameleon cosmology where the boundary of the universe is assumed to be enclosed by the dynamical apparent horizon. From a thermodynamic point of view, to link between thermodynamic and geometric parameters in cosmological models, we introduce "entropy rate of change multiplied by the temperature" as a model independent thermodynamic state parameter together with the well known $\{r,s \}$ statefinder to differentiate the dark energy models.
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arXiv:1106.1773
The generalized second law in chameleon cosmology
Authors: H. Farajollahi, A. Salehi, F. Tayebi
(Submitted on 9 Jun 2011)
10 pages, 6 figures; To be published in Can. J. Phys
In this paper, we investigate the validity of the generalized second law (GSL) of thermodynamics in flat FRW chameleon cosmology where the boundary of the universe is assumed to be enclosed by the dynamical apparent horizon. It has been shown that, in a bouncing scenario for the universe with phantom crossing, the total entropy decreases with time in the contracting epoch, whereas, the dynamics of the internal and horizon entropies depends on the behavior of both equation of state and hubble parameters.
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Xiv:1106.2211
Tachyon Field in Intermediate Inflation on the Brane
Authors: H. Farajollahi, A. Ravanpak
(Submitted on 11 Jun 2011)
7 pages, 4 figures
We propose a new model of inflation in the framework of brane cosmology in the presence of tachyonic field. we derive the expressions for the model parameters in brane inflation, and estimate the observable parameters numerically and find them to fit with the observational data.
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arXiv:1106.2659
Interacting Holographic dark energy in chameleon tachyon cosmology
Authors: H. Farajollahi, A. Ravanpak, G. Farpour Fadakar
(Submitted on 14 Jun 2011)
12 pages, 12 figures; will be published in Astrophys. Space Sci
We propose in this paper an interacting holographic dark energy (IHDE) model in chameleon--tachyon cosmology by interaction between the components of the dark sectors. In the formalism, the interaction term emerges from the scalar field coupling matter lagrangian in the model rather than being inserted into the formalism as an external source for the interaction. The correspondence between the tachyon field and the holographic dark energy (HDE) densities allows to reconstruct the tachyon scalar field and its potential in a flat FRW universe. The model can show the accelerated expansion of the universe and satisfies the observational data.
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arXiv:1106.4414
Dynamics of the universe as a "test 3-brane" in a 5D bulk
Authors: Hossein Farajollahi, Arvin Ravanpak
(Submitted on 22 Jun 2011)
11 pages, 12 figures; will be published in Can. J. Phys
In this paper we study the dynamics of a 5D bulk space-time with our universe as a "test 3-brane" located in the bulk, an idealized model of a topological object whose physical properties is negligible in comparison with that of the bulk. Our universe experiences acceleration and its equation of state parameter crosses the phantom divide line due to the geometry of the bulk space-time.
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arXiv:1010.1587
Dielectric Analog Space-Times
Authors: Robert T. Thompson, Jörg Frauendiener
(Submitted on 8 Oct 2010 (v1), last revised 7 Jan 2011 (this version, v2))
10 pages, 1 figure
We generalize the notion of a dielectric analog Schwarzschild black hole model to analog models of arbitrary space-times; in particular, the approach is not restricted to static space-times. This is done by establishing a correspondence between electrodynamics on a curved, vacuum manifold, with electrodynamics in a general linear dielectric residing in Minkowski space-time. The mapping is not unique, allowing for some freedom in the specification of equivalent materials, which could be useful for exploiting recent developments in the production of metamaterials. Some examples are considered, with special attention paid to the dielectric analog of the exterior Kerr geometry, which is found to be reproducible with regular, linear, dielectrics.
Journal reference: Phys.Rev.D82:124021,2010
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arXiv:1102.1867
A note on the post-Newtonian limit of quasi-local energy expressions
Authors: Jörg Frauendiener, László B Szabados
(Submitted on 9 Feb 2011)
10 pages
An 'effective' quasi-local energy expression, motivated by the (relativistically corrected) Newtonian theory, is suggested in static spacetimes. In asymptotically flat spacetimes this expression tends to the ADM energy at the spatial infinity as a {\em monotonically decreasing} set function. We prove its positivity in spherically symmetric spacetimes under certain energy conditions, and that its vanishing characterizes flatness.
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arXiv:1105.0109
Studying null and time-like geodesics in the classroom
Authors: Thomas Müller, Jörg Frauendiener
(Submitted on 30 Apr 2011)
13 pages, 9 figures
In a first course of general relativity it is usually quite difficult for students to grasp the concept of a geodesic. It is supposed to be straight (auto-parallel) and yet it 'looks' curved. In these situations it is very useful to have some explicit examples available which show the different behaviour of geodesics. In this paper we present the GeodesicViewer, an interactive tool for studying the behaviour of geodesics in many different space-times. The geodesics can be represented in several ways, depending on the space-time in question. The use of a local reference frame and 'Cartesian-like' coordinates helps the students to develop some intuition in various situations. We present the various features of the GeodesicViewer in the form of readily formulated exercises for the students.
Journal reference: Eur. J. Phys. 32, 747 (2011)
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arXiv:1105.5008
Witten spinors on maximal, conformally flat hypersurfaces
Authors: Jörg Frauendiener, James M. Nester, László B. Szabados
(Submitted on 25 May 2011)
22 pages
The boundary conditions that exclude zeros of the solutions of the Witten equation (and hence guarantee the existence of a 3-frame satisfying the so-called special orthonormal frame gauge conditions) are investigated. We determine the general form of the conformally invariant boundary conditions for the Witten equation, and find the boundary conditions that characterize the constant and the conformally constant spinor fields among the solutions of the Witten equations on compact domains in extrinsically and intrinsically flat, and on maximal, intrinsically globally conformally flat spacelike hypersurfaces, respectively. We also provide a number of exact solutions of the Witten equation with various boundary conditions (both at infinity and on inner or outer boundaries) that single out nowhere vanishing spinor fields on the flat, non-extreme Reissner--Nordstr\"om and Brill--Lindquist data sets. Our examples show that
there is an interplay between the boundary conditions, the global topology of the hypersurface and the existence/non-existence of zeros of the solutions of the Witten equation.
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arXiv:0909.2076
Rotating Odd-Parity Lorentz Invariance Test in Electrodynamics
Authors: Michael E. Tobar, Eugene N. Ivanov, Paul L. Stanwix, Jean-Michel G. le Floch, John G. Hartnett
(Submitted on 11 Sep 2009 (v1), last revised 25 Nov 2009 (this version, v2))
We report the first operation of a rotating odd-parity Lorentz Invariance test in electrodynamics using a microwave Mach-Zehnder interferometer with permeable material in one arm. The experiment sets a direct bound to $ \kappa_{tr}$ of $-0.3\pm 3\times10^{-7}$. Using new power recycled waveguide interferometer techniques (with the highest spectral resolution ever achieved of $2\times10^{-11} rad/\sqrt{Hz}$) we show an improvement of several orders of magnitude is attainable in the future.
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arXiv:0910.0240
Black holes and neutron stars in the generalized tensor-vector-scalar theory
Authors: Paul D. Lasky
(Submitted on 1 Oct 2009)
Bekenstein's Tensor-Vector-Scalar (TeVeS) theory has had considerable success as a relativistic theory of Modified Newtonian Dynamics (MoND). However, recent work suggests that the dynamics of the theory are fundamentally flawed and numerous authors have subsequently begun to consider a generalization of TeVeS where the vector field is given by an Einstein-Aether action. Herein, I develop strong-field solutions of the generalized TeVeS theory, in particular exploring neutron stars as well as neutral and charged black holes. I find that the solutions are identical to the neutron star and black hole solutions of the original TeVeS theory, given a mapping between the parameters of the two theories, and hence provide constraints on these values of the coupling constants. I discuss the consequences of these results in detail including the stability of such spacetimes as well as generalizations to more complicated geometries.
Journal reference: Phys.Rev.D80:081501,2009
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arXiv:1001.1159
The effect of pressure gradients on luminosity distance - redshift relations
Authors: Paul D. Lasky, Krzysztof Bolejko
(Submitted on 7 Jan 2010)
Inhomogeneous cosmological models have had significant success in explaining cosmological observations without the need for dark energy. Generally, these models imply inhomogeneous matter distributions alter the observable relations that are taken for granted when assuming the Universe evolves according to the standard Friedmann equations. Moreover, it has recently been shown that both inhomogeneous matter and pressure distributions are required in both early and late stages of cosmological evolution. These associated pressure gradients are required in the early Universe to sufficiently describe void formation, whilst late-stage pressure gradients stop the appearance of anomalous singularities. In this paper we investigate the effect of pressure gradients on cosmological observations by deriving the luminosity distance - redshift relations in spherically symmetric, inhomogeneous spacetimes endowed with a
perfect fluid. By applying this to a specific example for the energy density distribution and using various equations of state, we are able to explicitly show that pressure gradients may have a non-negligble effect on cosmological observations. In particular, we show that a non-zero pressure gradient can imply significantly different residual Hubble diagrams for $z\lesssim1$ compared to when the pressure is ignored. This paper therefore highlights the need to properly consider pressure gradients when interpreting cosmological observations.
Journal reference: Class. Quantum Grav. (2010) 27, 035011
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arXiv:1011.0747
Stability and Quasinormal Modes of Black holes in Tensor-Vector-Scalar theory: Scalar Field Perturbations
Authors: Paul D. Lasky, Daniela D. Doneva
(Submitted on 2 Nov 2010 (v1), last revised 4 Jan 2011 (this version, v2))
The imminent detection of gravitational waves will trigger precision tests of gravity through observations of quasinormal ringing of black holes. While General Relativity predicts just two polarizations of gravitational waves, the so-called plus and cross polarizations, numerous alternative theories of gravity predict up to six different polarizations which will potentially be observed in current and future generations of gravitational wave detectors. Bekenstein's Tensor-Vector-Scalar (TeVeS) theory and its generalization fall into one such class of theory that predict the full gamut of six polarizations of gravitational waves. In this paper we begin the study of quasinormal modes (QNMs) in TeVeS by studying perturbations of the scalar field in a spherically symmetric background. We show that, at least in the case where superluminal propagation of perturbations is not present, black holes are generically stable to this
kind of perturbation. We also make a unique prediction that, as the limit of the various coupling parameters of the theory tend to zero, the QNM spectrum tends to $1/\sqrt{2}$ times the QNM spectrum induced by scalar perturbations of a Schwarzschild black hole in General Relativity due to the intrinsic presence of the background vector field. We further show that the QNM spectrum does not vary significantly from this value for small values of the theory's coupling parameters, however can vary by as much as a few percent for larger, but still physically relevant parameters.
Journal reference: Phys.Rev.D82:124068,2010
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arXiv:1105.1895
Hydromagnetic Instabilities in Neutron Stars
Authors: Paul D. Lasky, Burkhard Zink, Kostas D. Kokkotas, Kostas Glampedakis
(Submitted on 10 May 2011 (v1), last revised 24 May 2011 (this version, v2))
Abstract: We model the non-linear ideal magnetohydrodynamics of poloidal magnetic fields in neutron stars in general relativity assuming a polytropic equation of state. We identify familiar hydromagnetic modes, in particular the 'sausage/varicose' mode and 'kink' instability inherent to poloidal magnetic fields. The evolution is dominated by the kink instability, which causes a cataclysmic reconfiguration of the magnetic field. The system subsequently evolves to new, non-axisymmetric, quasi-equilibrium end-states. The existence of this branch of stable quasi-equilibria may have consequences for magnetar physics, including flare generation mechanisms and interpretations of quasi-periodic oscillations.
Journal reference: 2011 ApJ 735, L20
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arXiv:1003.4777
McVittie's Legacy: Black Holes in an Expanding Universe
Authors: Nemanja Kaloper, Matthew Kleban, Damien Martin
(Submitted on 24 Mar 2010 (v1), last revised 28 Jul 2010 (this version, v3))
23 pages
We prove that a class of solutions to Einstein's equations---originally discovered by G. C. McVittie in 1933---includes regular black holes embedded in Friedman-Robertson-Walker cosmologies. If the cosmology is dominated at late times by a positive cosmological constant, the metric is regular everywhere on and outside the black hole horizon and away from the big bang singularity, and the solutions asymptote in the future and near the horizon to the Schwarzschild-de Sitter geometry. For solutions without a positive cosmological constant the would-be horizon is a weak null singularity.
Journal reference: Phys.Rev.D81:104044,2010
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arXiv:1007.2939
On the role of shear in cosmological averaging
Authors: Maria Mattsson, Teppo Mattsson
(Submitted on 17 Jul 2010)
17 pages, 3 figures
Using the spherically symmetric inhomogeneous Lemaitre-Tolman-Bondi dust solution, we study how the shear and the backreaction depend on the sharpness of the spatial transition between voids and walls and on the size of the voids. The voids considered here are regions with matter density Omega ~ 0 and expansion rate Ht ~ 1, while the walls are regions with matter density Omega ~ 1 and expansion rate Ht ~ 2/3. The results indicate that both the volume-average shear and the variance of the expansion rate grow proportional to the sharpness of the transition and diverge in the limit of a step function, but, for realistic-sized voids, are virtually independent of the size of the void. However, the backreaction, given by the difference of the variance and the shear, has a finite value in the step-function limit. By comparing the exact result for the backreaction to the case where the shear is neglected by treating the voids and
walls as separate Friedmann-Robertson-Walker models, we find that the shear suppresses the backreaction by a factor of (r_0/t_0)^2, the squared ratio of the void size to the horizon size. This exemplifies the importance of using the exact solution for the interface between the regions of different expansion rates and densities. The suppression is justified to hold also for a network of compensated voids, but may not hold if the universe is dominated by uncompensated voids.
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arXiv:1012.4008
On the role of shear in cosmological averaging II: large voids, non-empty voids and a network of different voids
Authors: Maria Mattsson, Teppo Mattsson
(Submitted on 17 Dec 2010)
19 pages, 5 figures
We study the effect of shear on the cosmological backreaction in the context of matching voids and walls together using the exact inhomogeneous Lemaitre-Tolman-Bondi solution. Generalizing JCAP 1010 (2010) 021, we allow the size of the voids to be arbitrary and the densities of the voids and walls to vary in the range 0 < Omega_v < Omega_w < 1. We derive the exact analytic result for the backreaction and consider its series expansion in powers of the ratio of the void size to the horizon size, r_0/t_0. In addition, we deduce a very simple fitting formula for the backreaction with error less than 1% for voids up to sizes r_0 = t_0. We also construct an exact solution for a network of voids with different sizes and densities, leading to a non-zero relative variance of the expansion rate between the voids. While the leading order term of the backreaction for a single void-wall pair is of order (r_0/t_0)^2, the relative
variance between the different voids in the network is found to be of order (r_0/t_0)^4 and thus very small for voids of the observed size. Furthermore, we show that even for very large voids, the backreaction is suppressed by an order of magnitude relative to the estimate obtained by treating the walls and voids as disjoint Friedmann solutions. Whether the suppression of the backreaction due to the shear is just a consequence of the restrictions of the used exact models, or a generic feature, has to be addressed with more sophisticated solutions.
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arXiv:0908.0290
The performance of arm locking in LISA
Authors: Kirk McKenzie, Robert E. Spero, Daniel A. Shaddock
(Submitted on 3 Aug 2009 (v1), last revised 4 Aug 2009 (this version, v2))
28 pages, 36 figures
For the laser interferometer space antenna (LISA) to reach it's design sensitivity, the coupling of the free running laser frequency noise to the signal readout must be reduced by more than 14 orders of magnitude. One technique employed to reduce the laser frequency noise will be arm locking, where the laser frequency is locked to the LISA arm length. This paper details an implementation of arm locking, studies orbital effects, the impact of errors in the Doppler knowledge, and noise limits. The noise performance of arm locking is calculated with the inclusion of the dominant expected noise sources: ultra stable oscillator (clock) noise, spacecraft motion, and shot noise. Studying these issues reveals that although dual arm locking [A. Sutton & D. A Shaddock, Phys. Rev. D 78, 082001 (2008).] has advantages over single (or common) arm locking in terms of allowing high gain, it has disadvantages in both laser frequency pulling
and noise performance. We address this by proposing a hybrid sensor, retaining the benefits of common and dual arm locking sensors. We present a detailed design of an arm locking controller and perform an analysis of the expected performance when used with and without laser pre-stabilization. We observe that the sensor phase changes beneficially near unity-gain frequencies of the arm-locking controller, allowing a factor of 10 more gain than previously believed, without degrading stability. We show that the LISA frequency noise goal can be realized with arm locking and Time-Delay Interferometry only, without any form of pre-stabilization.
Journal reference: Phys.Rev.D80:102003,2009
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arXiv:1005.2176
Experimental Demonstration of Time-Delay Interferometry for the Laser Interferometer Space Antenna
Authors: Glenn de Vine, Brent Ware, Kirk McKenzie, Robert E. Spero, William M. Klipstein, Daniel A. Shaddock
(Submitted on 12 May 2010)
4 pages, 4 figures
We report on the first demonstration of time-delay interferometry (TDI) for LISA, the Laser Interferometer Space Antenna. TDI was implemented in a laboratory experiment designed to mimic the noise couplings that will occur in LISA. TDI suppressed laser frequency noise by approximately 10^9 and clock phase noise by 6x10^4, recovering the intrinsic displacement noise floor of our laboratory test bed. This removal of laser frequency noise and clock phase noise in post-processing marks the first experimental validation of the LISA measurement scheme.
Journal reference: Phys.Rev.Lett.104:211103,2010
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arXiv:1102.0799
Progress in Interferometry for LISA at JPL
Authors: Robert Spero, Brian Bachman, Glenn de Vine, Jeffrey Dickson, William Klipstein, Tetsuo Ozawa, Kirk McKenzie, Daniel Shaddock, David Robison, Andrew Sutton, Brent Ware
(Submitted on 3 Feb 2011 (v1), last revised 7 Feb 2011 (this version, v2))
11 pages, 9 figures
Recent advances at JPL in experimentation and design for LISA interferometry include the demonstration of Time Delay Interferometry using electronically separated end stations, a new arm-locking design with improved gain and stability, and progress in flight readiness of digital and analog electronics for phase measurements.
Journal reference: Class.Quant.Grav.28:094007,2011
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arXiv:0911.1609
Gravitational Radiation from Hydrodynamic Turbulence in a Differentially Rotating Neutron Star
Authors: A. Melatos, C. Peralta
(Submitted on 9 Nov 2009)
The mean-square current quadrupole moment associated with vorticity fluctuations in high-Reynolds-number turbulence in a differentially rotating neutron star is calculated analytically, as are the amplitude and decoherence time of the resulting, stochastic gravitational wave signal. The calculation resolves the subtle question of whether the signal is dominated by the smallest or largest turbulent eddies: for the Kolmogorov-like power spectrum observed in superfluid spherical Couette simulations, the wave strain is controlled by the largest eddies, and the decoherence time approximately equals the maximum eddy turnover time. For a neutron star with spin frequency $\nu_s$ and Rossby number $Ro$, at a distance $d$ from Earth, the root-mean-square wave strain reaches $h_{RMS} \approx 3\times 10^{-24} Ro^3 (\nu_s / 30 Hz)^3 (d/1 kpc)^{-1}$. A cross-correlation search can detect such a source in principle, because the
signal decoheres over the time-scale $\tau_c \approx 10^{-3} Ro^{-1} (\nu_s / 30 Hz)^{-1} s$, which is adequately sampled by existing long-baseline interferometers. Hence hydrodynamic turbulence imposes a fundamental noise floor on gravitational wave observations of neutron stars, although its polluting effect may be muted by partial decoherence in the hectohertz band, where current continuous-wave searches are concentrated, for the highest frequency (and hence most powerful) sources.
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arXiv:1005.2257
Gravitational-wave spin-down and stalling lower limits on the electrical resistivity of the accreted mountain in a millisecond pulsar
Authors: Matthias Vigelius, Andrew Melatos
(Submitted on 13 May 2010)
The electrical resistivity of the accreted mountain in a millisecond pulsar is limited by the observed spin-down rate of binary radio millisecond pulsars (BRMSPs) and the spins and X-ray fluxes of accreting millisecond pulsars (AMSPs). We find $\eta \ge 10^{-28}\,\mathrm{s}\, (\tau_\mathrm{SD}/1\,\mathrm{Gyr})^{-0.8}$ (where $\tau_\mathrm{SD}$ is the spin-down age) for BRMSPs and $\eta \ge 10^{-25}\,\mathrm{s}\,(\dot{M}_\mathrm{a}/\dot{M}_\mathrm{E})^{0.6}$ (where $\dot{M}_\mathrm{a}$ and $\dot{M}_\mathrm{E}$ are the actual and Eddington accretion rates) for AMSPs. These limits are inferred assuming that the mountain attains a steady state, where matter diffuses resistively across magnetic flux surfaces but is replenished at an equal rate by infalling material. The mountain then relaxes further resistively after accretion ceases. The BRMSP spin-down limit approaches the theoretical electron-impurity resistivity at
temperatures $\ga 10^5$ K for an impurity concentration of $\sim 0.1$, while the AMSP stalling limit falls two orders of magnitude below the theoretical electron-phonon resistivity for temperatures above $10^8$ K. Hence BRMSP observations are already challenging theoretical resistivity calculations in a useful way. Next-generation gravitational-wave interferometers will constrain $\eta$ at a level that will be competitive with electromagnetic observations.
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arXiv:1102.4654
Designing a cross-correlation search for continuous-wave gravitational radiation from a neutron star in the supernova remnant SNR 1987A
Authors: Christine Chung, Andrew Melatos, Badri Krishnan, John T. Whelan
(Submitted on 23 Feb 2011)
17 pages, 5 figures, accepted for publication in MNRAS
A strategy is devised for a semi-coherent cross-correlation search for a young neutron star in the supernova remnant SNR 1987A, using science data from the Initial LIGO and/or Virgo detectors. An astrophysical model for the gravitational wave phase is introduced which describes the star's spin down in terms of its magnetic field strength $B$ and ellipticity $\epsilon$, instead of its frequency derivatives. The model accurately tracks the gravitational wave phase from a rapidly decelerating neutron star under the restrictive but computationally unavoidable assumption of constant braking index, an issue which has hindered previous searches for such young objects. The theoretical sensitivity is calculated and compared to the indirect, age-based wave strain upper limit. The age-based limit lies above the detection threshold in the frequency band 75\,Hz $\lesssim \nu \lesssim 450$\,Hz. The semi-coherent phase metric is also
calculated and used to estimate the optimal search template spacing for the search. The range of search parameters that can be covered given our computational resources ($\sim 10^9$ templates) is also estimated. For Initial LIGO sensitivity, in the frequency band between 50\,Hz and 500\,Hz, in the absence of a detected signal, we should be able to set limits of $B \gtrsim 10^{11}$\,G and $\epsilon \lesssim 10^{-4}$.
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arXiv:0901.2568
Simple cosmological de Sitter solutions on dS$_4 \times Y_6$ spaces
Authors: Ishwaree P. Neupane
(Submitted on 19 Jan 2009 (v1), last revised 1 Feb 2010 (this version, v4))
15 pages
Explicit time-dependent solutions of the 10D vacuum Einstein equations are found for which spacetime is compactified on six-dimensional warped spaces. We explicitly work out an example where the internal manifold is a six-dimensional generalized space having positive, negative or zero scalar curvature, whose base can be a five-sphere $S^5$ or an Einstein space $T^{1,1}=(S^2\times S^2)\rtimes S^1$. In this paper, inflationary de Sitter solutions are found just by solving the 10D vacuum Einstein equations. Our results further show that the limitation with warped models studied to date has arisen partly from an oversimplification of the 10D metric ansatz. We also give some explicit examples of a non-singular warped compactification on de Sitter space dS$_4$.
Journal reference: Class. Quant. Grav.27:045011, 2010
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arXiv:0902.1532
Constraining the runaway dilaton and quintessential dark energy
Authors: Ishwaree P. Neupane, Holly Trowland
(Submitted on 10 Feb 2009 (v1), last revised 10 Mar 2010 (this version, v3))
32 pages
Dark Energy is some of the weirdest and most mysterious stuff in the universe that tends to increase the rate of expansion of the universe. Two commonly known forms of dark energy are the cosmological constant, a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli whose energy density can vary with time. We explore one particular model for dynamic dark energy; quintessence driven by a scalar dilaton field. We propose an ansatz for the form of the dilaton field, $|\phi(a)|/m_P \equiv \alpha_1 \ln t+ \alpha_2 t^n=\alpha\ln a+ \beta\, a^{2\zeta}$, where $a$ is the scale factor and $\alpha$ and $\zeta$ are parameters of the model. This phenomenological ansatz for $\phi$ can be motivated by generic solutions of a scalar dilaton field in many effective string theory and string-inspired gravity models in four dimensions. Using a compilation of current data including type
Ia supernovae, we impose observational constraints on the slope parameters like $\alpha$ and $\zeta$ and then discuss the relation of our results to analytical constrains on various cosmological parameters, including the dark energy equation of state. Sensible constraints are imposed on model parameters like $\alpha$ and $\zeta$ as well as on the dark energy/dark matter couplings using results from structure formation. The constraints of this model are shown to encompass the cosmological constant limit within $1\sigma$ error bars.
Journal reference: Int.J.Mod.Phys.D19:367-394,2010
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arXiv:0903.4190
Extra dimensions, warped compactifications and cosmic acceleration
Authors: Ishwaree P. Neupane
(Submitted on 25 Mar 2009 (v1), last revised 22 Dec 2009 (this version, v4))
10 pages
We report on explicit cosmological solutions within the framework of an inflating de Sitter brane embedded in five- and ten-dimensional bulk spacetimes. In the specific example we study the brane tension is induced by the curvature related to the expansion of a physical 3+1 spacetime rather than by a bulk cosmological term. In a generic situation with nonzero brane tension, the expansion of the universe accelerates eventually. We also show that inflationary cosmology is possible for a wide class of metrics without violating four- and higher-dimensional null energy condition.
Journal reference: Phys.Lett.B683:88-95,2010
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arXiv:0904.4805
Black Holes, Entropy Bound and Causality Violation
Authors: Ishwaree P Neupane
(Submitted on 30 Apr 2009)
8 pages
The gravity/gauge theory duality has provided us a way of studying QCD at short distances from straightforward calculations in classical general relativity. Among numerous results obtained so far, one of the most striking is the universality of the ratio of the shear viscosity to the entropy density. For all gauge theories with Einstein gravity dual, this ratio is \eta/s=1/4\pi. However, in general higher-curvature gravity theories, including two concrete models under discussion - the Gauss-Bonnet gravity and the (Riemann)^2 gravity - the ratio \eta/s can be smaller than 1/4\pi (thus violating the conjecture bound), equal to 1/4\pi or even larger than 1/4\pi. As we probe spacetime at shorter distances, there arises an internal inconsistency in the theory, such as a violation of microcausality, which is correlated with a classical limit on black hole entropy.
Journal reference: Int.J.Mod.Phys.A24:3584-3591,2009
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arXiv:0905.2774
Accelerating universe from warped extra dimensions
Authors: Ishwaree P Neupane
(Submitted on 17 May 2009 (v1), last revised 23 Oct 2009 (this version, v3))
7 pages
Accelerating universe or the existence of a small and positive cosmological constant is probably the most pressing obstacle as well as opportunity to significantly improving the models of four-dimensional cosmology from fundamental theories of gravity, including string theory. In seeking to resolve this problem, one naturally wonders if the real world can somehow be interpreted as an inflating de Sitter brane embedded in a higher-dimensional spacetime described by warped geometry. In this scenario, the four-dimensional cosmological constant may be uniquely determined in terms of two length scales: one is a scale associated with the size of extra dimensions and the other is a scale associated with the expansion rate of our universe. In some specific cases, these two scales are complementary to each other. This result is demonstrated here by presenting some explicit and completely non-singular de Sitter space
dS$_4$ solutions of vacuum Einstein equations in five and ten dimensions.
Journal reference: Class. Quant. Grav. 26: 195008, 2009
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The warping of extra spaces accelerates the expansion of the universe
Authors: Ishwaree P Neupane
(Submitted on 1 Apr 2010 (v1), last revised 30 Nov 2010 (this version, v2))
7 pages, Selected for an "Honorable Mention" (15 May 2010) in the Gravity Research Foundation 2010 Awards for Essays on Gravitation
Generic cosmological models derived from higher dimensional theories with warped extra dimensions have a nonzero cosmological constant-like term induced on the 3+1 space-time, or a physical 3-brane. In the scenario where this 3+1 space-time is an inflating de Sitter "brane" embedded in a higher-dimensional space-time, described by warped geometry, the 4D cosmological term is determined in terms of two length scales: one is a scale associated with the size of extra dimension(s) and the other is a scale associated with the warping of extra space(s). The existence of this term in four dimensions provides a tantalizing possibility of explaining the observed accelerating expansion of the universe from fundamental theories of gravity, e.g. string theory.
Journal reference: Int. J. Mod. Phys. D19: 2281-2287, 2010
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arXiv:1006.4495
Warped compactification on curved manifolds
Authors: Ishwaree P. Neupane
(Submitted on 23 Jun 2010 (v1), last revised 26 Apr 2011 (this version, v5))
24 pages, 1 figure
The characterization of a six- (or seven)-dimensional internal manifold with metric as having positive, zero or negative curvature is expected to be an important aspect of warped compactifications in supergravity. In this context, Douglas and Kallosh recently pointed out that a compact internal space with negative curvature could help to construct four-dimensional de Sitter solutions only if the extra dimensions are strongly warped or there are large stringy corrections. That is, the problem of finding 4-dimensional de Sitter solutions is well posed, if all extra dimensions are physically compact, which is called a no-go theorem. Here, we show that the above conclusion does not extend to a general class of warped compactifications in classical supergravity that allow a non-compact direction or cosmological solutions for which the internal space is asymptotic to a cone over a product of compact Einstein spaces or spheres.
For clarity, we present classical solutions that compactify higher-dimensional spacetime to produce a Robertson--Walker universe with de Sitter-type expansion plus one extra non-compact direction. Such models are found to admit both an effective four-dimensional Newton constant that remains finite and a normalizable zero-mode graviton wavefunction. We also exhibit the possibility of obtaining 4D de Sitter solutions by including the effect of fluxes (p-form field strengths).
Journal reference: Class.Quant.Grav.28:125015,2011
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arXiv:1011.5007
Warped compactification to de Sitter space
Authors: Ishwaree P. Neupane
(Submitted on 23 Nov 2010 (v1), last revised 15 Feb 2011 (this version, v2))
19 pages, 2 figures
We explore in detail the prospects of obtaining a four-dimensional de Sitter universe in classical supergravity models with warped and time-independent extra dimensions, presenting explicit cosmological solutions of the $(4+n)$-dimensional Einstein equations with and without a bulk cosmological constant term. For the first time in the literature we show that there may exist a large class of warped supergravity models with a noncompact extra dimension which lead to a finite 4D Newton constant as well as a massless 4D graviton localised on an inflating four-dimensional FLRW universe. This result helps establish that the `no-go' theorem forbidding acceleration in `standard' compactification of string/M-theory on physically compact spaces should not apply to a general class of warped supergravity models that allows at least one noncompact direction. We present solutions for which the size of the radial dimension
takes a constant value in the large volume limit, providing an explicit example of spontaneous compactification.
Journal reference: Nucl.Phys.B847:549-566,2011
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arXiv:1011.6357
De Sitter brane-world, localization of gravity, and the cosmological constant
Authors: Ishwaree P. Neupane
(Submitted on 29 Nov 2010 (v1), last revised 31 Mar 2011 (this version, v2))
10 pages, 5 figures
Cosmological models with a de Sitter 3-brane embedded in a five-dimensional de Sitter spacetime (dS5) give rise to a finite 4D Planck mass similar to that in Randall-Sundrum (RS) brane-world models in AdS5 spacetime. Yet there arise a few important differences as compared to the results with a flat 3-brane or 4D Minkowski spacetime. For example, the mass reduction formula (MRF) $M_{Pl}^2=M_{5}^3 \ell_{AdS}$ as well as the relationship $M_{Pl}^2= M_{Pl(4+n)}^{n+2} L^{n}$ (with $L$ being the average size or the radius of the $n$ extra dimensions) expected in models of product-space (or Kaluza-Klein) compactifications get modified in cosmological backgrounds. In an expanding universe, a physically relevant MRF encodes information upon the four-dimensional Hubble expansion parameter, in addition to the length and mass parameters $L$, $M_{Pl}$ and $M_{Pl (4+n)}$. If a bulk cosmological constant is present in the solution, then
the reduction formula is further modified. With these new insights, we show that the localization of a massless 4D graviton as well as the mass hierarchy between $M_{Pl}$ and $M_{Pl (4+n)}$ can be explained in cosmological brane-world models. A notable advantage of having a 5D de Sitter bulk is that in this case the zero-mass wavefunction is normalizable, which is not necessarily the case if the bulk spacetime is anti de Sitter. In spacetime dimensions $D\ge 7$, however, the bulk cosmological constant $\Lambda_b$ can take either sign ($\Lambda_b <0$, $=0$, or $>0$). The D=6 case is rather inconclusive, in which case $\Lambda_b$ may be introduced together with 2-form gauge field (or flux).
Journal reference: Phys.Rev.D83:086004,2011
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arXiv:1106.3721
We Probably Live On An Inflating Brane-World
Authors: Ishwaree P. Neupane
(Submitted on 19 Jun 2011)
8 pages (Essay received Honourable mention in Gravity Research Foundation essay competition 2011)
Brane-world models where observers are trapped within the thickness of a 3-brane offer novel perspectives on gravitation and cosmology. In this essay, I would argue that the problem of a late epoch acceleration of the universe is well explained in the framework of a 4-dimensional de Sitter universe embedded in a 5-dimensional de Sitter spacetime. While a 5D anti de Sitter space background is important for studying conformal field theories -- for its role in the AdS/CFT correspondence -- the existence of a 5-dimensional de Sitter space is crucial for finding an effective 4D Newton constant that remains finite and a normalizable zero-mode graviton wave function.
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arXiv:0905.0006
The alternative to classical mass renormalization for tube-based self-force calculations
Authors: Andrew H. Norton
(Submitted on 30 Apr 2009)
21 pages, 2 figures
To date, classical mass renormalization has been invoked in all tube-based self-force calculations, thus following the method introduced in Dirac's 1938 calculation of the electromagnetic self-force for the classical radiating electron. In this paper a new tube method is described that does not rely on a mass renormalization procedure. As a result, exact self-force calculations become possible for classical radiating systems of finite size. A new derivation of the Lorentz-Dirac equation is given and the relationship between the new tube method and the classical mass renormalization procedure is explained. It is expected that a similar tube method could be used to obtain rigorous results in the gravitational self-force problem.
Journal reference: Class. Quantum Grav. 26 (2009) 105009
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arXiv:0901.0215
The universe as a black hole in isotropic coordinates
Authors: Nikodem J. Poplawski
(Submitted on 2 Jan 2009)
4 pages
We show that the radial geodesic motion of a particle inside a black hole in isotropic coordinates (the Einstein-Rosen bridge) is physically different from the radial motion inside a Schwarzschild black hole. A particle enters the interior region of an Einstein-Rosen black hole which is regular and physically equivalent to the asymptotically flat exterior of a white hole, and the particle's proper time extends to infinity. Because the motion across the Einstein-Rosen bridge is unidirectional, and the surface of a black hole is the event horizon for distant observers, an Einstein-Rosen black hole is indistinguishable from a Schwarzschild black hole for such observers. Observers inside an Einstein-Rosen black hole perceive its interior as a closed universe that began when the black hole formed, with an initial radius equal to the Schwarzschild radius of the black hole $r_g$, and with an initial accelerated expansion.
Therefore the model of a universe as a black hole in isotropic coordinates explains the origin of cosmic inflation. We show that this kind of inflation corresponds to the effective cosmological constant $\Lambda=3/r_g^2$, which, for the smallest astrophysical black holes, is $~10^{-8}m^{-2}$. If we assume that our Universe is the interior of an Einstein-Rosen black hole, astronomical observations give the time of inflation $~10^{-3}s$ and the size of the Universe at the end of the inflationary epoch $~10^{32}m$.
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arXiv:0902.1994
Radial motion into an Einstein-Rosen bridge
Authors: Nikodem J. Poplawski
(Submitted on 11 Feb 2009 (v1), last revised 13 Apr 2010 (this version, v3))
7 pages
We consider the radial geodesic motion of a massive particle into a black hole in isotropic coordinates, which represents the exterior region of an Einstein-Rosen bridge (wormhole). The particle enters the interior region, which is regular and physically equivalent to the asymptotically flat exterior of a white hole, and the particle's proper time extends to infinity. Since the radial motion into a wormhole after passing the event horizon is physically different from the motion into a Schwarzschild black hole, Einstein-Rosen and Schwarzschild black holes are different, physical realizations of general relativity. Yet for distant observers, both solutions are indistinguishable. We show that timelike geodesics in the field of a wormhole are complete because the expansion scalar in the Raychaudhuri equation has a discontinuity at the horizon, and because the Einstein-Rosen bridge is represented by the Kruskal diagram
with Rindler's elliptic identification of the two antipodal future event horizons. These results suggest that observed astrophysical black holes may be Einstein-Rosen bridges, each with a new universe inside that formed simultaneously with the black hole. Accordingly, our own Universe may be the interior of a black hole existing inside another universe.
Journal reference: Phys.Lett.B687:110-113, 2010
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arXiv:0905.4284
Torsion as electromagnetism and spin
Authors: Nikodem J. Poplawski
(Submitted on 26 May 2009 (v1), last revised 10 Jul 2010 (this version, v2))
6 pages
We show that it is possible to formulate the classical Einstein-Maxwell-Dirac theory of spinors interacting with the gravitational and electromagnetic fields as the Einstein-Cartan-Kibble-Sciama theory with the Ricci scalar of the traceless torsion, describing gravity, and the torsion trace acting as the electromagnetic potential.
Journal reference: Int.J.Theor.Phys.49:1481-1488,2010
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arXiv:0910.1181
Nonsingular Dirac particles in spacetime with torsion
Authors: Nikodem J. Poplawski
(Submitted on 7 Oct 2009 (v1), last revised 29 Oct 2010 (this version, v2))
8 pages
We use the Papapetrou method of multipole expansion to show that a Dirac field in the Einstein-Cartan-Kibble-Sciama (ECKS) theory of gravity cannot form singular configurations concentrated on one- or two-dimensional surfaces in spacetime. Instead, such a field describes a nonsingular particle whose spatial dimension is at least on the order of its Cartan radius. In particular, torsion modifies Burinskii's model of the Dirac electron as a Kerr-Newman singular ring of the Compton size, by replacing the ring with a toroidal structure with the outer radius of the Compton size and the inner radius of the Cartan size. We conjecture that torsion produced by spin prevents the formation of singularities from matter composed of quarks and leptons. We expect that the Cartan radius of an electron, ~10^{-27} m, introduces an effective ultraviolet cutoff in quantum field theory for fermions in the ECKS spacetime. We also
estimate a maximum density of matter to be on the order of the corresponding Cartan density, ~10^{51} kg m^{-3}, which gives a lower limit for black-hole masses ~10^{16} kg. This limit corresponds to energy ~10^{43} GeV which is 39 orders of magnitude larger than the maximum beam energy currently available at the LHC. Thus, if torsion exists and the ECKS theory of gravity is correct, the LHC cannot produce micro black holes.
Journal reference: Phys.Lett.B690:73-77,2010
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arXiv:0911.0334
Spacetime and fields
Authors: Nikodem J. Poplawski
(Submitted on 2 Nov 2009)
114 pages
We present a self-contained introduction to the classical theory of spacetime and fields. The order of the presentation is: 1. Spacetime (tensors, affine connection, curvature, metric, tetrad and spin connection, Lorentz group, spinors), 2. Fields (principle of least action, action for gravitational field, matter, symmetries and conservation laws, gravitational field equations, spinor fields, electromagnetic field).
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arXiv:1001.4324
Einstein-Cartan gravity excludes extra dimensions
Authors: Nikodem J. Poplawski
(Submitted on 25 Jan 2010)
3 pages
We show that the electron in the Riemann-Cartan spacetime with extra dimensions has a finite size that is much larger than the experimental upper limit on its radius. Thus the Arkani-Hamed-Dimopoulos-Dvali and Randall-Sundrum models of the weak/Planck hierarchy in particle physics are not viable if spin produces torsion according to the Einstein-Cartan theory of gravity.
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arXiv:1005.0893
Cosmological constant from quarks and torsion
Authors: Nikodem J. Poplawski
(Submitted on 6 May 2010 (v1), last revised 4 Jul 2011 (this version, v3))
4 pages
We present a simple and natural way to derive the observed small, positive cosmological constant from the gravitational interaction of condensing fermions. In the Riemann-Cartan spacetime, torsion gives rise to the axial-axial four-fermion interaction term in the Dirac Lagrangian for spinor fields. We show that this nonlinear term acts like a cosmological constant if these fields have a nonzero vacuum expectation value. For quark fields in QCD, such a torsion-induced cosmological constant is positive and its energy scale is only about 8 times larger than the observed value. Adding leptons to this picture could lower this scale to the observed value.
Journal reference: Annalen Phys. 523: 291-295,2011
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arXiv:1007.0587
Cosmology with torsion: An alternative to cosmic inflation
Authors: Nikodem J. Poplawski
(Submitted on 4 Jul 2010 (v1), last revised 2 Nov 2010 (this version, v2))
8 pages
We propose a simple scenario which explains why our Universe appears spatially flat, homogeneous and isotropic. We use the Einstein-Cartan-Kibble-Sciama (ECKS) theory of gravity which naturally extends general relativity to include the spin of matter. The torsion of spacetime generates gravitational repulsion in the early Universe filled with quarks and leptons, preventing the cosmological singularity: the Universe expands from a state of minimum but finite radius. We show that the dynamics of the closed Universe immediately after this state naturally solves the flatness and horizon problems in cosmology because of an extremely small and negative torsion density parameter, $\Omega_S \approx -10^{-69}$. Thus the ECKS gravity provides a compelling alternative to speculative mechanisms of standard cosmic inflation. This scenario also suggests that the contraction of our Universe preceding the bounce at the
minimum radius may correspond to the dynamics of matter inside a collapsing black hole existing in another universe, which could explain the origin of the Big Bang.
Journal reference: Phys.Lett.B694:181-185,2010; Erratum-ibid.B701:672,2011
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arXiv:1101.4012
Matter-antimatter asymmetry and dark matter from torsion
Authors: Nikodem J. Poplawski
(Submitted on 20 Jan 2011 (v1), last revised 26 May 2011 (this version, v2))
5 pages
We propose a simple scenario which explains the observed matter-antimatter imbalance and the origin of dark matter in the Universe. We use the Einstein-Cartan-Sciama-Kibble theory of gravity which naturally extends general relativity to include the intrinsic spin of matter. Spacetime torsion produced by spin generates, in the classical Dirac equation, the Hehl-Datta term which is cubic in spinor fields. We show that under a charge-conjugation transformation this term changes sign relative to the mass term. A classical Dirac spinor and its charge conjugate therefore satisfy different field equations. Fermions in the presence of torsion have higher energy levels than antifermions, which leads to their decay asymmetry. Such a difference is significant only at extremely high densities that existed in the very early Universe. We propose that this difference caused a mechanism, according to which heavy fermions existing in
such a Universe and carrying the baryon number decayed mostly to normal matter, whereas their antiparticles decayed mostly to hidden antimatter which forms dark matter. The conserved total baryon number of the Universe remained zero.
Journal reference: Phys.Rev.D83:084033,2011
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arXiv:1102.5667
Four-fermion interaction from torsion as dark energy
Authors: Nikodem J. Poplawski
(Submitted on 28 Feb 2011)
4 pages
The observed small, positive cosmological constant may originate from the four-fermion interaction generated by spin and torsion in the Einstein-Cartan-Sciama-Kibble gravity if the fermions are condensing. We study how such an interaction is affected by adding two terms to the Dirac Lagrangian density: the parity-violating pseudoscalar density dual to the curvature tensor and a spinor-bilinear scalar density which measures the nonminimal coupling of fermions to torsion.
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arXiv:1103.4192
On the mass of the Universe born in a black hole
Authors: Nikodem J. Poplawski
(Submitted on 22 Mar 2011)
5 pages
It is shown, using the Einstein-Cartan-Sciama-Kibble theory of gravity, that gravitational collapse of spin-fluid fermionic matter with a stiff equation of state in a black hole of mass $M$ forms a new universe of mass $\sim M_\ast=M^2 m_n/m_\textrm{Pl}^2$, where $m_n$ is the mass of a neutron. Equaling $M_\ast$ to the mass of the Universe, which is about $10^{26}$ solar masses, gives $M\sim 10^3$ solar masses. Our Universe may thus have originated from the interior of an intermediate-mass black hole.
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arXiv:1105.0102
Neutral-meson oscillations with torsion
Authors: Nikodem J. Poplawski
(Submitted on 30 Apr 2011)
3 pages
We propose a simple mechanism that may explain the observed particle-antiparticle asymmetry in the Universe. In the Einstein-Cartan-Sciama-Kibble theory of gravity, the intrinsic spin of matter generates spacetime torsion. Classical Dirac fields in the presence of torsion obey the nonlinear Hehl-Datta equation which is asymmetric under a charge-conjugation transformation. Accordingly, at extremely high densities that existed in the very early Universe, fermions have higher effective masses than antifermions. As a result, a meson composed of a light quark and a heavy antiquark has a lower effective mass than its antiparticle. Neutral-meson oscillations in thermal equilibrium therefore favor the production of light quarks and heavy antiquarks, which may be related to baryogenesis.
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arXiv:1105.6127
Big bounce from spin and torsion
Authors: Nikodem J. Poplawski
(Submitted on 30 May 2011)
4 pages
The Einstein-Cartan-Sciama-Kibble theory of gravity naturally extends general relativity to account for the intrinsic spin of matter. Spacetime torsion, generated by spin, induces gravitational repulsion in fermionic matter at extremely high densities and prevents the formation of singularities. Accordingly, the big bang is replaced by a bounce that occurred when the energy density $\epsilon\propto gT^4$ was on the order of $n^2/m_\textrm{Pl}^2$, where $n\propto gT^3$ is the fermion number density and $g$ is the number of thermal degrees of freedom. If the early Universe contained only the known standard-model particles ($g\approx 100$), then the energy density at the big bounce was on the Planck scale where quantum gravity should be used. If, however, much more fermions existed at extremely high energies ($g\gg 100$), then the spin-torsion coupling caused a bounce below the Planck scale, where the classical description of
gravity is valid. Such a classical bounce prevents the matter in the contracting Universe from reaching the conditions at which a loop-quantum-gravity bounce would happen.
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arXiv:1106.4859
Spacetime torsion as a possible remedy to major problems in gravity and cosmology
Authors: Nikodem J. Poplawski
(Submitted on 23 Jun 2011)
5 pages
We show that the Einstein-Cartan-Sciama-Kibble theory of gravity with torsion not only extends general relativity to account for the intrinsic spin of matter, but it may also eliminate major problems in gravitational physics and answer major questions in cosmology. These problems and questions include: the origin of the Universe, the existence of singularities in black holes, the nature of inflation and dark energy, the origin of the matter-antimatter asymmetry in the Universe, and the nature of dark matter.
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arXiv:1001.2823
Quiescent cosmology and the final state of the universe
Authors: Philipp A Hoehn, Susan M Scott
(Submitted on 18 Jan 2010)
7 pages, 3 figures, essay receiving honorable mention in the 2007 Gravity Research Foundation Essay awards
It has long been a primary objective of cosmology to understand the apparent isotropy in our universe and to provide a mathematical formulation for its evolution. A school of thought for its explanation is quiescent cosmology, which already possesses a mathematical framework, namely the definition of an Isotropic Singularity, but only for the initial state of the universe. A complementary framework is necessary in order to also describe possible final states of the universe. Our new definitions of an Anisotropic Future Endless Universe and an Anisotropic Future Singularity, whose structure and properties differ significantly from those of the Isotropic Singularity, offer a promising realisation for this framework. The combination of the three definitions together may then provide the first complete formalisation of the quiescent cosmology concept.
Journal reference: Int. J. Mod. Phys. D. 17 (2008) 571
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arXiv:1001.2928
Encoding cosmological futures with conformal structures
Authors: Philipp A Hoehn, Susan M Scott
(Submitted on 18 Jan 2010)
35 pages, 9 figures
Quiescent cosmology and the Weyl curvature hypothesis possess a mathematical framework, namely the definition of an Isotropic Singularity, but only for the initial state of the universe. A complementary framework is necessary to also encode appropriate cosmological futures. In order to devise a new framework we analyse the relation between regular conformal structures and (an)isotropy, the behaviour and role of a monotonic conformal factor which is a function of cosmic time, as well as four example cosmologies for further guidance. Finally, we present our new definitions of an Anisotropic Future Endless Universe and an Anisotropic Future Singularity which offer a promising realisation for the new framework. Their irregular, degenerate conformal structures differ significantly from those of the Isotropic Singularity. The combination of the three definitions together could then provide the first
complete formalisation of the quiescent cosmology concept. For completeness we also present the new definitions of an Isotropic Future Singularity and a Future Isotropic Universe. The relation to other approaches, in particular to the somewhat dual dynamical systems approach, and other asymptotic scenarios is briefly discussed.
Journal reference: Class. Quant. Grav. 26 (2009) 035019
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arXiv:1001.4029
Conformal formulation of cosmological futures
Authors: Philipp A Hoehn, Susan M Scott
(Submitted on 22 Jan 2010)
3 pages, to appear in the proceedings of the 12th Marcel Grossmann Meeting, Paris, July 2009
We summarise the new conformal framework of an Anisotropic Future Endless Universe and an Anisotropic Future Singularity. Both new definitions are motivated by, but not restricted to quiescent cosmology and the Weyl curvature hypothesis, which previously only possessed a framework for a classical initial state of the universe, namely the Isotropic Singularity. Some of the features of the framework are briefly discussed.
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arXiv:1104.3378
A Correspondence Between Distances and Embeddings for Manifolds: New Techniques for Applications of the Abstract Boundary
Authors: Ben E. Whale, Susan M. Scott
(Submitted on 18 Apr 2011)
23 pages
We present a one-to-one correspondence between equivalence classes of embeddings of a manifold (into a larger manifold of the same dimension) and equivalence classes of certain distances on the manifold. This correspondence allows us to use the Abstract Boundary to describe the structure of the `edge' of our manifold without resorting to structures external to the manifold itself. This is particularly important in the study of singularities within General Relativity where singularities lie on this `edge'. The ability to talk about the same objects, e.g., singularities, via different structures provides alternative routes for investigation which can be invaluable in the pursuit of physically motivated problems where certain types of information are unavailable or difficult to use.
Journal reference: Journal of Geometry and Physics, Vol. 61, No. 5. (07 May 2011), pp. 927-939
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arXiv:0908.3665
X-Pipeline: An analysis package for autonomous gravitational-wave burst searches
Authors: Patrick J. Sutton, Gareth Jones, Shourov Chatterji, Peter Michael Kalmus, Isabel Leonor, Stephen Poprocki, Jameson Rollins, Antony Searle, Leo Stein, Massimo Tinto, Michal Was
(Submitted on 25 Aug 2009 (v1), last revised 7 Apr 2010 (this version, v2))
18 pages, 10 figures
Autonomous gravitational-wave searches -- fully automated analyses of data that run without human intervention or assistance -- are desirable for a number of reasons. They are necessary for the rapid identification of gravitational-wave burst candidates, which in turn will allow for follow-up observations by other observatories and the maximum exploitation of their scientific potential. A fully automated analysis would also circumvent the traditional "by hand" setup and tuning of burst searches that is both labourious and time consuming. We demonstrate a fully automated search with X-Pipeline, a software package for the coherent analysis of data from networks of interferometers for detecting bursts associated with GRBs and other astrophysical triggers. We discuss the methods X-Pipeline uses for automated running, including background estimation, efficiency studies, unbiased optimal tuning of search thresholds, and
prediction of upper limits. These are all done automatically via Monte Carlo with multiple independent data samples, and without requiring human intervention. As a demonstration of the power of this approach, we apply X-Pipeline to LIGO data to search for gravitational-wave emission associated with GRB 031108. We find that X-Pipeline is sensitive to signals approximately a factor of 2 weaker in amplitude than those detectable by the cross-correlation technique used in LIGO searches to date. We conclude with the prospects for running X-Pipeline as a fully autonomous, near real-time triggered burst search in the next LSC-Virgo Science Run.
Journal reference: New J.Phys.12:053034,2010
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arXiv:1005.0012
Singular value decomposition applied to compact binary coalescence gravitational-wave signals
Authors: Kipp Cannon, Adrian Chapman, Chad Hanna, Drew Keppel, Antony C. Searle, Alan J. Weinstein
(Submitted on 30 Apr 2010 (v1), last revised 10 Sep 2010 (this version, v2))
4 figures, 6 pages
We investigate the application of the singular value decomposition to compact-binary, gravitational-wave data-analysis. We find that the truncated singular value decomposition reduces the number of filters required to analyze a given region of parameter space of compact binary coalescence waveforms by an order of magnitude with high reconstruction accuracy. We also compute an analytic expression for the expected signal-loss due to the singular value decomposition truncation.
Journal reference: Phys.Rev.D82:044025,2010
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arXiv:1101.0584
Composite gravitational-wave detection of compact binary coalescence
Authors: Kipp Cannon, Chad Hanna, Drew Keppel, Antony C. Searle
(Submitted on 3 Jan 2011)
6 pages, 3 figures
The detection of gravitational waves from compact binaries relies on a computationally burdensome processing of gravitational-wave detector data. The parameter space of compact-binary-coalescence gravitational waves is large and optimal detection strategies often require nearly redundant calculations. Previously, it has been shown that singular value decomposition of search filters removes redundancy. Here we will demonstrate the use of singular value decomposition for a composite detection statistic. This can greatly improve the prospects for a computationally feasible rapid detection scheme across a large compact binary parameter space.
Journal reference: Phys.Rev.D83:084053,2011
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arXiv:0909.0650
An overview of the Laser Interferometer Space Antenna
Authors: Daniel A. Shaddock
(Submitted on 3 Sep 2009)
6 pages, 3 figures
The Laser Interferometer Space Antenna will detect gravitational waves with frequencies from 0.1 mHz to 1 Hz. This article provides a brief overview of LISA's science goals followed by a tutorial of the LISA measurement concept.
Journal reference: Publ.Astron.Soc.Austral.26:128-132,2009
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arXiv:1009.5855
Supernova tests of the timescape cosmology
Authors: Peter R. Smale, David L. Wiltshire
(Submitted on 29 Sep 2010 (v1), last revised 2 Dec 2010 (this version, v2))
21 pages, 9 figures
The timescape cosmology has been proposed as a viable alternative to homogeneous cosmologies with dark energy. It realises cosmic acceleration as an apparent effect that arises in calibrating average cosmological parameters in the presence of spatial curvature and gravitational energy gradients that grow large with the growth of inhomogeneities at late epochs. Recently Kwan, Francis and Lewis [arXiv:0902.4249] have claimed that the timescape model provides a relatively poor fit to the Union and Constitution supernovae compilations, as compared to the standard Lambda CDM model. We show this conclusion is a result of systematic issues in supernova light curve fitting, and of failing to exclude data below the scale of statistical homogeneity, z < 0.033. Using all currently available supernova datasets (Gold07, Union, Constitution, MLCS17, MLCS31, SDSS-II, CSP, Union2), and making cuts at the statistical homogeneity
scale, we show that data reduced by the SALT/SALT-II fitters provides Bayesian evidence that favours the spatially flat Lambda CDM model over the timescape model, whereas data reduced with MLCS2k2 fitters gives Bayesian evidence which favours the timescape model over the Lambda CDM model. We discuss the questions of extinction and reddening by dust, and of intrinsic colour variations in supernovae which do not correlate with the decay time, and the likely impact these systematics would have in a scenario consistent with the timescape model.
Journal reference: Mon. Not. R. Astron. Soc. 413 (2011) 367-385
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arXiv:0903.5046
Detecting Free-Mass Common-Mode Motion Induced by Incident Gravitational Waves: Testing General Relativity and Source Direction via Fox-Smith and Michelson Interferometers
Authors: Michael Edmund Tobar, Toshikazu Suzuki, Kazuaki Kuroda
(Submitted on 29 Mar 2009)
Posting of a paper published in 1999, which calculated the cross section of an interferometric gravitational wave detector to scalar and vector GW radiation
In this paper we show that information on both the differential and common mode free-mass response to a gravitational wave can provide important information on discriminating the direction of the gravitational wave source and between different theories of gravitation. The conventional Michelson interferometer scheme only measures the differential free-mass response. By changing the orientation of the beam splitter, it is possible to configure the detector so it is sensitive to the common-mode of the free-mass motion. The proposed interferometer is an adaptation of the Fox-Smith interferometer. A major limitation to the new scheme is its enhanced sensitivity to laser frequency fluctuations over the conventional, and we propose a method of canceling these fluctuations. The configuration could be used in parallel to the conventional differential detection scheme with a significant sensitivity and bandwidth.
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arXiv:0904.0055
Nanogap Transducer for Broadband Gravitational Wave Detection
Authors: Guilherme L. Pimentel, Odylio D. Aguiar, Michael E. Tobar, Joaquim J. Barroso, Rubens de M. Marinho
(Submitted on 1 Apr 2009 (v1), last revised 6 Oct 2009 (this version, v2))
7 pages, 4 figures
By changing from a resonant multimode paradigm to a free mass paradigm for transducers in resonant mass gravitational wave detection, an array of six spheres can achieve a sensitivity response curve competitive with interferometers, being as sensitive as GEO600 and TAMA300 in the 3 to 6 kHz band and more sensitive than LIGO for 50 percent of the 6 to 10 kHz band. We study how to assemble a klystron resonant cavity that has a 1 nm gap by understanding the stability of the forces applied at it (Casimir force, elastic force, weight). This approach has additional benefits. First, due to the relatively inexpensive nature of this technology (around US$ 1 million), it is accessible to a broader part of the world scientific community. Additionally, spherical resonant mass detectors have the ability to discern both the direction and polarization resolutions.
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arXiv:0912.2803
Testing Local Lorentz and Position Invariance and Variation of Fundamental Constants by searching the Derivative of the Comparison Frequency Between a Cryogenic Sapphire Oscillator and Hydrogen Maser
Authors: Michael Edmund Tobar, Peter Wolf, Sebastien Bize, Giorgio Santarelli, Victor Flambaum
(Submitted on 15 Dec 2009 (v1), last revised 16 Dec 2009 (this version, v2))
The cryogenic sapphire oscillator (CSO) at the Paris Observatory has been continuously compared to various Hydrogen Masers since 2001. The early data sets were used to test Local Lorentz Invariance in the Robertson-Mansouri-Sexl (RMS) framework by searching for sidereal modulations with respect to the Cosmic Microwave Background, and represent the best Kennedy-Thorndike experiment to date. In this work we present continuous operation over a period of greater than six years from September 2002 to December 2008 and present a more precise way to analyze the data by searching the time derivative of the comparison frequency. Due to the long-term operation we are able to search both sidereal and annual modulations. The results gives P_{KT} = \beta_{RMS}-\alpha_{RMS}-1 = -1.7(4.0) \times 10^{-8} for the sidereal and -23(10) \times 10^{-8} for the annual term, with a weighted mean of -4.8(3.7) \times 10^{-8}, a factor of 8 better than
previous. Also, we analyze the data with respect to a change in gravitational potential for both diurnal and annual variations. The result gives \beta_{H-Maser} - \beta_{CSO} = -2.7(1.4) \times 10^{-4} for the annual and -6.9(4.0) \times 10^{-4} for the diurnal terms, with a weighted mean of -3.2(1.3) \times 10^{-4}. This result is two orders of magnitude better than other tests that use electromagnetic resonators. With respect to fundamental constants a limit can be provided on the variation with ambient gravitational potential and boost of a combination of the fine structure constant (\alpha), the normalized quark mass (m_q), and the electron to proton mass ratio (m_e/m_p), setting the first limit on boost dependence of order 10^{-10}.
Journal reference: Phys.Rev.D81:022003,2010
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arXiv:1006.1376
Improved Constraints on Isotropic Shift and Anisotropies of the Speed of Light using Rotating Cryogenic Sapphire Oscillators
Authors: Michael A. Hohensee, Paul. L. Stanwix, Michael Edmund Tobar, Stephen R. Parker, David F. Phillips, Ronald L. Walsworth
(Submitted on 7 Jun 2010)
We demonstrate that Michelson-Morley tests, which detect direction-dependent anisotropies in the speed of light, can also be used to place limits upon isotropic deviations of the vacuum speed of light from $c$, as described by the photon sector Standard Model Extension (SME) parameter $\tilde{\kappa}_{tr}$. A shift in the speed of light that is isotropic in one inertial frame implies anisotropic shifts in others. Using observer Lorentz covariance, we derive the time-dependent variations in the relative resonance frequencies of a pair of electromagnetic resonators that would be generated by such a shift in the rest frame of the Sun. A new analysis of a recent experimental test of relativity using this result constrains $\tilde{\kappa}_{tr}$ with a precision of $7.4\times10^{-9}$. This represents the first constraint on $\tilde{\kappa}_{tr}$ by a Michelson-Morley experiment and the first analysis
of a single experiment to simultaneously set limits on all nine non-birefringent terms in the photon sector of the SME.
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arXiv:1102.0081
Cavity Bounds on Higher-Order Lorentz-Violating Coefficients
Authors: Stephen R. Parker, Matthew Mewes, Michael E. Tobar, Paul L. Stanwix
(Submitted on 1 Feb 2011 (v1), last revised 6 Apr 2011 (this version, v2))
4 pages, 1 figure
We determine the sensitivity of a modern Michelson-Morley resonant-cavity experiment to the higher-order nonbirefringent and nondispersive coefficients of the Lorentz-violating Standard-Model Extension. Data from a recent year-long run of the experiment is used to place the first bounds on these coefficients.
Journal reference: Phys.Rev.Lett.106:180401,2011
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arXiv:0812.3744
Signature change events: A challenge for quantum gravity?
Authors: Angela White (Newcastle upon Tyne), Silke Weinfurtner (UBC Vancouver), Matt Visser (Victoria University of Wellington)
(Submitted on 19 Dec 2008 (v1), last revised 6 Jan 2010 (this version, v3))
33 pages. 4 figures
Within the framework of either Euclidian (functional-integral) quantum gravity or canonical general relativity the signature of the manifold is a priori unconstrained. Furthermore, recent developments in the emergent spacetime programme have led to a physically feasible implementation of signature change events. This suggests that it is time to revisit the sometimes controversial topic of signature change in general relativity. Specifically, we shall focus on the behaviour of a quantum field subjected to a manifold containing regions of different signature. We emphasise that, regardless of the underlying classical theory, there are severe problems associated with any quantum field theory residing on a signature-changing background. (Such as the production of what is naively an infinite number of particles, with an infinite energy density.) From the viewpoint of quantum gravity phenomenology, we discuss
possible consequences of an effective Lorentz symmetry breaking scale. To more fully understand the physics of quantum fields exposed to finite regions of Euclidean-signature (Riemannian) geometry, we show its similarities with the quantum barrier penetration problem, and the super-Hubble horizon modes encountered in cosmology. Finally we raise the question as to whether signature change transitions could be fully understood and dynamically generated within (modified) classical general relativity, or whether they require the knowledge of a full theory of quantum gravity.
Journal reference: Class.Quant.Grav.27:045007,2010
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arXiv:0901.4365
Black holes in general relativity
Authors: Matt Visser (Victoria University of Wellington)
(Submitted on 28 Jan 2009 (v1), last revised 5 Feb 2009 (this version, v3))
16 pages; 7 figures
What is going on (as of August 2008) at the interface between theoretical general relativity, string-inspired models, and observational astrophysics? Quite a lot. In this mini-survey I will make a personal choice and focus on four specific questions: Do black holes "exist"? (For selected values of the word "exist".) Is black hole formation and evaporation unitary? Can one mimic a black hole to arbitrary accuracy? Can one detect the presence of a horizon using local physics?
Journal reference: PoS BHs,GRandStrings 2008:001,2008
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arXiv:0902.0346
Small, dark, and heavy: But is it a black hole?
Authors: Matt Visser (Victoria University of Wellington), Carlos Barcelo (Astrophysics Institute of Andalusia), Stefano Liberati (SISSA and INFN, Trieste), Sebastiano Sonego (University of Udine)
(Submitted on 2 Feb 2009 (v1), last revised 9 Feb 2009 (this version, v2))
17 pages, 8 figures
Astronomers have certainly observed things that are small, dark, and heavy. But are these objects really black holes in the sense of general relativity? The consensus opinion is simply "yes", and there is very little "wriggle room". We discuss one of the specific alternatives.
Journal reference: PoS BHs,GRandStrings 2008:010,2008
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arXiv:0902.0590
Lorentz symmetry breaking as a quantum field theory regulator
Authors: Matt Visser (Victoria University of Wellington)
(Submitted on 3 Feb 2009 (v1), last revised 17 Jul 2009 (this version, v3))
15 pages; 3 figures
Perturbative expansions of relativistic quantum field theories typically contain ultraviolet divergences requiring regularization and renormalization. Many different regularization techniques have been developed over the years, but most regularizations require severe mutilation of the logical foundations of the theory. In contrast, breaking Lorentz invariance, while it is certainly a radical step, at least does not damage the logical foundations of the theory. We shall explore the features of a Lorentz symmetry breaking regulator in a simple polynomial scalar field theory, and discuss its implications. We shall quantify just "how much" Lorentz symmetry breaking is required to fully regulate the theory and render it finite. This scalar field theory provides a simple way of understanding many of the key features of Horava's recent article [arXiv:0901.3775 [hep-th]] on 3+1 dimensional quantum gravity.
Journal reference: Phys.Rev.D80:025011,2009
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arXiv:0903.2128
Birkhoff-like theorem for rotating stars in (2+1) dimensions
Authors: Jozef Skakala (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 12 Mar 2009 (v1), last revised 22 Mar 2009 (this version, v3))
4 pages
Abstract: Consider a rotating and possibly pulsating "star" in (2+1) dimensions. If the star is axially symmetric, then in the vacuum region surrounding the star, (a region that we assume at most contains a cosmological constant), the Einstein equations imply that under physically plausible conditions the geometry is in fact stationary. Furthermore, the geometry external to the star is then uniquely guaranteed to be the (2+1) dimensional analogue of the Kerr-de Sitter spacetime, the BTZ geometry. This Birkhoff-like theorem is very special to (2+1) dimensions, and fails in (3+1) dimensions. Effectively, this is a "no hair" theorem for (2+1) dimensional axially symmetric stars: the exterior geometry is completely specified by the mass, angular momentum, and cosmological constant.
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arXiv:0904.4464
Phenomenologically viable Lorentz-violating quantum gravity
Authors: Thomas P. Sotiriou (U Maryland), Matt Visser (Victoria University of Wellington), Silke Weinfurtner (UBC Vancouver)
(Submitted on 28 Apr 2009 (v1), last revised 26 Jun 2009 (this version, v3))
4 pages
Horava's "Lifschitz point gravity" has many desirable features, but in its original incarnation one is forced to accept a non-zero cosmological constant of the wrong sign to be compatible with observation. We develop an extension of Horava's model that abandons "detailed balance", and in 3+1 dimensions exhibit all five marginal (renormalizable) and four relevant (super-renormalizable) operators, as determined by power counting. We also consider the classical limit of this theory, evaluate the Hamiltonian and super-momentum constraints, and extract the classical equations of motion in a form similar to the ADM formulation of general relativity. This puts the model in a framework amenable to developing detailed precision tests.
Journal reference: Phys.Rev.Lett.102:251601,2009
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arXiv:0905.2798
Quantum gravity without Lorentz invariance
Authors: Thomas P Sotiriou (Cambridge University), Matt Visser (Victoria University of Wellington), Silke Weinfurtner (UBC Vancouver)
(Submitted on 18 May 2009 (v1), last revised 13 Oct 2009 (this version, v3))
36 pages
There has been a significant surge of interest in Horava's model for 3+1 dimensional quantum gravity, this model being based on anisotropic scaling at a z=3 Lifshitz point. Horava's model, and its variants, show dramatically improved ultra-violet behaviour at the cost of exhibiting violation of Lorentz invariance at ultra-high momenta. Following up on our earlier note, [arXiv:0904.4464 [hep-th]], we discuss in more detail our variant of Horava's model. In contrast to Horava's original model, we abandon "detailed balance" and restore parity invariance. We retain, however, Horava's "projectability condition" and explore its implications. Under these conditions, we explicitly exhibit the most general model, and extract the full classical equations of motion in ADM form. We analyze both spin-2 and spin-0 graviton propagators around flat Minkowski space. We furthermore analyze the classical evolution of FLRW
cosmologies in this model, demonstrating that the higher-derivative spatial curvature terms can be used to mimic radiation fluid and stiff matter. We conclude with some observations concerning future prospects.
Journal reference: JHEP 0910:033,2009
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arXiv:0905.4530
Signature-change events in emergent spacetimes with anisotropic scaling
Authors: Silke Weinfurtner (University of British Columbia), Angela White (Newcastle University), Matt Visser (Victoria University of Wellington)
(Submitted on 28 May 2009)
9 pages
We investigate the behaviour of quantum fields coupled to a spacetime geometry exhibiting finite regions of Euclidean (Riemannian) signature. Although from a gravity perspective this situation might seem somewhat far fetched, we will demonstrate its direct physical relevance for an explicitly realizable condensed matter system whose linearized perturbations experience an effective emergent spacetime geometry with externally controllable signature. This effective geometry is intrinsically quantum in origin, and its signature is determined by the details of the microscopic structure. At the level of the effective field theory arising from our condensed matter system we encounter explicit anisotropic scaling in time and space. Here Lorentz symmetry is an emergent symmetry in the infrared. This anisotropic scaling of time and space cures some of the technical problems that arise when working within a
canonical quantisation scheme obeying strict Lorentz invariance at all scales, and so is helpful in permitting signature change events to take place.
Journal reference: J.Phys.Conf.Ser.189:012046,2009
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arXiv:0906.5407
Cosmographic analysis of dark energy
Authors: Matt Visser (Victoria University of Wellington), Celine Cattoen (Victoria University of Wellington)
(Submitted on 30 Jun 2009)
14 pages. To appear in the Proceedings of DARK 2009 -- The Seventh International Heidelberg Conference on Dark Matter in Astro and Particle Physics, Christchurch, New Zealand, January 2009
The Hubble relation between distance and redshift is a purely cosmographic relation that depends only on the symmetries of a FLRW spacetime, but does not intrinsically make any dynamical assumptions. This suggests that it should be possible to estimate the parameters defining the Hubble relation without making any dynamical assumptions. To test this idea, we perform a number of inter-related cosmographic fits to the legacy05 and gold06 supernova datasets, paying careful attention to the systematic uncertainties. Based on this supernova data, the "preponderance of evidence" certainly suggests an accelerating universe. However we would argue that (unless one uses additional dynamical and observational information, and makes additional theoretical assumptions) this conclusion is not currently supported "beyond reasonable doubt". As part of the analysis we develop two particularly transparent graphical
representations of the redshift-distance relation -- representations in which acceleration versus deceleration reduces to the question of whether the relevant graph slopes up or down.
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arXiv:0909.4157
Revisiting the semiclassical gravity scenario for gravitational collapse
Authors: C. Barcelo, S. Liberati, S. Sonego, M. Visser
(Submitted on 23 Sep 2009)
8 pages
The existence of extremely dark and compact astronomical bodies is by now a well established observational fact. On the other hand, classical General Relativity predicts the existence of black holes which fit very well with the observations, but do lead to important conceptual problems. In this contribution we ask ourselves the straightforward question: Are the dark and compact objects that we have observational evidence for black holes in the sense of General Relativity? By revising the semiclassical scenario of stellar collapse we find out that as the result of a collapse some alternative objects could be formed which might supplant black holes.
Journal reference: Physics and Mathematics of Gravitation, Proceedings of the Spanish Relativity Meeting (ERE 2008), eds. K.E. Kunze, M. Mars, M.A. Vazquez-Mozo, pag. 99-106, AIP Conf. Proc. 1122, 2009
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arXiv:1001.1180
The quantum interest conjecture in (3+1)-dimensional Minkowski space
Authors: Gabriel Abreu (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 7 Jan 2010)
3 pages
The quantum inequalities, and the closely related quantum interest conjecture, impose restrictions on the distribution of the energy density measured by any time-like observer, potentially preventing the existence of exotic phenomena such as Alcubierre warp-drives or traversable wormholes. It has already been proved that both assertions can be reduced to statements concerning the existence or non-existence of bound states of a certain 1-dimensional quantum mechanical Hamiltonian. Using this approach, we will informally review a simple variational proof of one version of the Quantum Interest conjecture in (3+1)-dimensional Minkowski space.
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arXiv:1001.1310
Acoustic geometry for general relativistic barotropic irrotational fluid flow
Authors: Matt Visser (Victoria University of Wellington), Carmen Molina-Paris (Leeds University)
(Submitted on 8 Jan 2010 (v1), last revised 6 May 2010 (this version, v2))
23 pages
"Acoustic spacetimes", in which techniques of differential geometry are used to investigate sound propagation in moving fluids, have attracted considerable attention over the last few decades. Most of the models currently considered in the literature are based on non-relativistic barotropic irrotational fluids, defined in a flat Newtonian background. The extension, first to special relativistic barotropic fluid flow, and then to general relativistic barotropic fluid flow in an arbitrary background, is less straightforward than it might at first appear. In this article we provide a pedagogical and simple derivation of the general relativistic "acoustic spacetime" in an arbitrary (d+1) dimensional curved-space background.
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arXiv:1002.0308
Projectable Horava-Lifshitz gravity in a nutshell
Authors: Silke Weinfurtner, Thomas P. Sotiriou, Matt Visser
(Submitted on 1 Feb 2010)
8 pages
Approximately one year ago Horava proposed a power-counting renormalizable theory of gravity which abandons local Lorentz invariance. The proposal has been received with growing interest and resulted in various different versions of Horava-Lifshitz gravity theories, involving a colourful potpourri of new terminology. In this proceedings contribution we first motivate and briefly overview the various different approaches, clarifying their differences and similarities. We then focus on a model referred to as projectable Horava-Lifshitz gravity and summarize the key results regarding its viability.
Journal reference: J. Phys.: Conf. Ser. 222, 012054 (2010)
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arXiv:1004.1456
Kodama time: Geometrically preferred foliations of spherically symmetric spacetimes
Authors: Gabriel Abreu (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 9 Apr 2010 (v1), last revised 13 Jul 2010 (this version, v3))
20 pages, accepted for publication in Physical Review
In a general time-dependent (3+1)-dimensional spherically symmetric spacetime, the so-called Kodama vector is a naturally defined geometric quantity that is timelike outside the evolving horizon and so defines a preferred class of fiducial observers. However the Kodama vector does not by itself define any preferred notion of time. We first extract as much information as possible by invoking the "warped product" structure of spherically symmetric spacetime to study the Kodama vector, and the associated Kodama energy flux, in a coordinate independent manner. Using this formalism we construct a general class of conservation laws, generalizing Kodama's energy flux. We then demonstrate that a preferred time coordinate - which we shall call Kodama time - can be introduced by taking the additional step of applying the Clebsch decomposition theorem to the Kodama vector. We thus construct a geometrically preferred
coordinate system for any time-dependent spherically symmetric spacetime, and explore its properties. We study the geometrically preferred fiducial observers, and demonstrate that it is possible to define and calculate a generalized notion of surface gravity that is valid throughout the entire evolving spacetime. Furthermore, by building and suitably normalizing set of radial null geodesics, we can show that this generalized surface gravity passes several consistency tests and has a physically appropriate static limit.
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arXiv:1004.2539
Semi-analytic results for quasi-normal frequencies
Authors: Jozef Skakala (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 15 Apr 2010 (v1), last revised 1 Sep 2010 (this version, v5))
28 pages, accepted for publication in JHEP
The last decade has seen considerable interest in the quasi-normal frequencies [QNFs] of black holes (and even wormholes), both asymptotically flat and with cosmological horizons. There is wide agreement that the QNFs are often of the form omega_n = (offset) + i n (gap), though some authors have encountered situations where this behaviour seems to fail. To get a better understanding of the general situation we consider a semi-analytic model based on a piecewise Eckart (Poeschl-Teller) potential, allowing for different heights and different rates of exponential falloff in the two asymptotic directions. This model is sufficiently general to capture and display key features of the black hole QNFs while simultaneously being analytically tractable, at least for asymptotically large imaginary parts of the QNFs. We shall derive an appropriate "quantization condition" for the asymptotic QNFs, and extract as much
analytic information as possible. In particular, we shall explicitly verify that the (offset)+ i n (gap) behaviour is common but not universal, with this behaviour failing unless the ratio of rates of exponential falloff on the two sides of the potential is a rational number. (This is "common but not universal" in the sense that the rational numbers are dense in the reals.) We argue that this behaviour is likely to persist for black holes with cosmological horizons.
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arXiv:1004.2734
General polarization modes for the Rosen gravitational wave
Authors: Bethan Cropp (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 15 Apr 2010 (v1), last revised 14 Jun 2010 (this version, v2))
12 pages
Abstract: Strong-field gravitational plane waves are often represented in either the Rosen or Brinkmann forms. While these two metric ansatze are related by a coordinate transformation, so that they should describe essentially the same physics, they rather puzzlingly seem to treat polarization states quite differently. Both ansatze deal equally well with + and X linear polarizations, but there is a qualitative difference in they way they deal with circular, elliptic, and more general polarization states. In this article we will develop a general formalism for dealing with arbitrary polarization states in the Rosen form of the gravitational wave metric, representing an arbitrary polarization by a trajectory in a suitably defined two dimensional hyperbolic plane.
Journal reference: Classical and Quantum Gravity 27 (2010) 165022
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arXiv:1005.1132
Tolman mass, generalized surface gravity, and entropy bounds
Authors: Gabriel Abreu (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 7 May 2010 (v1), last revised 29 Jun 2010 (this version, v3))
4 pages
In any static spacetime the quasi-local Tolman mass contained within a volume can be reduced to a Gauss-like surface integral involving the flux of a suitably defined generalized surface gravity. By introducing some basic thermodynamics and invoking the Unruh effect one can then develop elementary bounds on the quasi-local entropy that are very similar in spirit to the holographic bound, and closely related to entanglement entropy.
Journal reference: Physical Review Letters 105 (2010) 041302
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arXiv:1005.4483
Quasi-normal frequencies: Key analytic results
Authors: Petarpa Boonserm (Chulalongkorn University), Matt Visser (Victoria University of Wellington)
(Submitted on 25 May 2010 (v1), last revised 20 Jan 2011 (this version, v3))
31 pages
The study of exact quasi-normal modes [QNMs], and their associated quasi-normal frequencies [QNFs], has had a long and convoluted history - replete with many rediscoveries of previously known results. In this article we shall collect and survey a number of known analytic results, and develop several new analytic results - specifically we shall provide several new QNF results and estimates, in a form amenable for comparison with the extant literature. Apart from their intrinsic interest, these exact and approximate results serve as a backdrop and a consistency check on ongoing efforts to find general model-independent estimates for QNFs, and general model-independent bounds on transmission probabilities. Our calculations also provide yet another physics application of the Lambert W function. These ideas have relevance to fields as diverse as black hole physics, (where they are related to the damped oscillations of
astrophysical black holes, to greybody factors for the Hawking radiation, and to more speculative state-counting models for the Bekenstein entropy), to quantum field theory (where they are related to Casimir energies in unbounded systems), through to condensed matter physics, (where one may literally be interested in an electron tunelling through a physical barrier).
Journal reference: JHEP 1103:073,2011
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arXiv:1007.4039
Highly-damped quasi-normal frequencies for piecewise Eckart potentials
Authors: Jozef Skakala (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 23 Jul 2010 (v1), last revised 1 Sep 2010 (this version, v2))
4 pages
Highly-damped quasi-normal frequencies are very often of the form omega_n = (offset) + i n (gap). We investigate the genericity of this phenomenon by considering a model potential that is piecewise Eckart (piecewise Poeschl-Teller), and developing an analytic "quantization condition" for the highly-damped quasi-normal frequencies. We find that this omega_n = (offset) + i n (gap) behaviour is generic but not universal, with the controlling feature being whether or not the ratio of the rates of exponential falloff in the two asymptotic directions is a rational number. These observations are of direct relevance to any physical situation where highly-damped quasi-normal modes (damped modes) are important --- in particular (but not limited to) to black hole physics, both theoretical and observational.
Journal reference: Physical Review D81 (2010) 125023
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arXiv:1008.0689
Bi-metric pseudo-Finslerian spacetimes
Authors: Jozef Skakala (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 4 Aug 2010)
8 pages
Finsler spacetimes have become increasingly popular within the theoretical physics community over the last two decades. Because physicists need to use pseudo-Finsler structures to describe propagation}of signals, there will be nonzero null vectors in both the tangent and cotangent spaces --- this causes significant problems in that many of the mathematical results normally obtained for "usual" (Euclidean signature) Finsler structures either do not apply, or require significant modifications to their formulation and/or proof. We shall first provide a few basic definitions, explicitly demonstrating the interpretation of bi-metric theories in terms of pseudo-Finsler norms. We shall then discuss the tricky issues that arise when trying to construct an appropriate pseudo-Finsler metric appropriate to bi-metric spacetimes. Whereas in Euclidian signature the construction of the Finsler metric typically fails at the zero
vector, in Lorentzian signature the Finsler metric is typically ill-defined on the entire null cone.
Journal reference: J.Geom.Phys.61:1396-1400, 2011
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arXiv:1008.4639
Any spacetime has a Bianchi type I spacetime as a limit
Authors: Bethan Cropp (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 27 Aug 2010)
19 pages
Pick an arbitrary timelike geodesic in an arbitrary spacetime. We demonstrate that there is a particular limiting process, an "ultra-local limit", in which the immediate neighborhood of the timelike geodesic can be "blown up" to yield a general (typically non-diagonal) Bianchi type I spacetime. This process shares some (but definitely not all) of the features of the Penrose limit, whereby the immediate neighborhood of an arbitrary null geodesic is "blown up" to yield a pp-wave as a limit.
Journal reference: Class.Quant.Grav.28:055007,2011
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arXiv:1009.0080
Generic master equations for quasi-normal frequencies
Authors: Jozef Skakala (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 1 Sep 2010 (v1), last revised 23 Nov 2010 (this version, v2))
23 pages
Generic master equations governing the highly-damped quasi-normal frequencies [QNFs] of one-horizon, two-horizon, and even three-horizon spacetimes can be obtained through either semi-analytic or monodromy techniques. While many technical details differ, both between the semi-analytic and monodromy approaches, and quite often among various authors seeking to apply the monodromy technique, there is nevertheless widespread agreement regarding the the general form of the QNF master equations. Within this class of generic master equations we can establish some rather general results, relating the existence of "families" of QNFs of the form omega_{a,n} = (offset)_a + i n (gap) to the question of whether or not certain ratios of parameters are rational or irrational.
Journal reference: JHEP 1011:070,2010
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arXiv:1011.4538
Entropy bounds for uncollapsed matter
Authors: Gabriel Abreu (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 19 Nov 2010)
4 pages
Abstract: In any static spacetime the quasilocal Tolman mass contained within a volume can be reduced to a Gauss-like surface integral involving the flux of a suitably defined generalized surface gravity. By introducing some basic thermodynamics, and invoking the Unruh effect, one can then develop elementary bounds on the quasilocal entropy that are very similar in spirit to the holographic bound, and closely related to entanglement entropy.
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arXiv:1011.4634
Quasi-normal frequencies: Semi-analytic results for highly damped modes
Authors: Jozef Skakala, Matt Visser
(Submitted on 21 Nov 2010)
4 pages
Black hole highly-damped quasi-normal frequencies (QNFs) are very often of the form (offset)} + i n (gap). We have investigated the genericity of this phenomenon for the Schwarzschild--deSitter (SdS) black hole by considering a model potential that is piecewise Eckart (piecewise Poeschl-Teller), and developing an analytic ``quantization condition'' for the highly-damped quasi-normal frequencies. We find that the (offset) + i n(gap) behaviour is common but not universal, with the controlling feature being whether or not the ratio of the surface gravities is a rational number. We furthermore observed that the relation between rational ratios of surface gravities and periodicity of QNFs is very generic, and also occurs within different analytic approaches applied to various types of black hole spacetimes. These observations are of direct relevance to any physical situation where highly-damped quasi-normal modes are important.
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arXiv:1011.5593
Minimal conditions for the existence of a Hawking-like flux
Authors: Carlos Barcelo (IAA-CSIC, Granada), Stefano Liberati (SISSA, Trieste), Sebastiano Sonego (Universita di Udine), Matt Visser (Victoria University of Wellington)
(Submitted on 25 Nov 2010)
4 pages
We investigate the minimal conditions that an asymptotically flat general relativistic spacetime must satisfy in order for a Hawking-like Planckian flux of particles to arrive at future null infinity. We demonstrate that there is no requirement that any sort of horizon form anywhere in the spacetime. We find that the irreducible core requirement is encoded in an approximately exponential "peeling" relationship between affine coordinates on past and future null infinity. As long as a suitable adiabaticity condition holds, then a Planck-distributed Hawking-like flux will arrive at future null infinity with temperature determined by the e-folding properties of the outgoing null geodesics. The temperature of the Hawking-like flux can slowly evolve as a function of time. We also show that the notion of "peeling" of null geodesics is distinct, and in general different, from the usual notion of "inaffinity" used in Hawking's definition of surface gravity.
Journal reference: Phys.Rev.D83:041501,2011
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arXiv:1011.5904
Polarization modes for strong-field gravitational waves
Authors: Bethan Cropp (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 25 Nov 2010)
4 pages
Strong-field gravitational plane waves are often represented in either the Rosen or Brinkmann forms. These forms are related by a coordinate transformation, so they should describe essentially the same physics, but the two forms treat polarization states quite differently. Both deal well with linear polarizations, but there is a qualitative difference in the way they deal with circular, elliptic, and more general polarization states. In this article we will describe a general algorithm for constructing arbitrary polarization states in the Rosen form.
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arXiv:1011.5911
Hawking-like radiation from evolving black holes and compact horizonless objects
Authors: Carlos Barcelo (IAA-CSIC, Granada), Stefano Liberati (SISSA, Trieste), Sebastiano Sonego (Universita di Udine), Matt Visser (Victoria University of Wellington)
(Submitted on 26 Nov 2010 (v1), last revised 19 Jan 2011 (this version, v2))
34 pages
Usually, Hawking radiation is derived assuming (i) that a future eternal event horizon forms, and (ii) that the subsequent exterior geometry is static. However, one may be interested in either considering quasi-black holes (objects in an ever-lasting state of approach to horizon formation, but never quite forming one), where (i) fails, or, following the evolution of a black hole during evaporation, where (ii) fails. We shall verify that as long as one has an approximately exponential relation between the affine parameters on the null generators of past and future null infinity, then subject to a suitable adiabatic condition being satisfied, a Planck-distributed flux of Hawking-like radiation will occur. This happens both for the case of an evaporating black hole, as well as for the more dramatic case of a collapsing object for which no horizon has yet formed (or even will ever form). In this article we
shall cast the previous statement in a more precise and quantitative form, and subsequently provide several explicit calculations to show how the time-dependent Bogoliubov coefficients can be calculated.
Journal reference: JHEP 1102:003,2011
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arXiv:1012.2867
Entropy bounds for uncollapsed rotating bodies
Authors: Gabriel Abreu (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 13 Dec 2010 (v1), last revised 10 Mar 2011 (this version, v2))
Entropy bounds in black hole physics, based on a wide variety of different approaches, have had a long and distinguished history. Recently the current authors have turned attention to uncollapsed systems and obtained a robust entropy bound for uncollapsed static spherically symmetric configurations. In the current article we extend this bound to rotating systems. This extension is less simple than one might at first suppose. Purely classically, (using only classical general relativity and basic thermodynamics), it is possible to show that the entropy of uncollapsed matter inside a region enclosed by a surface of area A is bounded from above by S <= kappa(surface) A / (4 pi T). Here kappa(surface) is a suitably defined surface gravity. By appealing to the Unruh effect, which is our only invocation of quantum physics, we argue that for a suitable class of fiducial observers there is a lower bound on the temperature (as
measured at spatial infinity): T >= max kappa(FIDOs) / (2 pi). Thus, using only classical general relativity, basic thermodynamics, and the Unruh effect, we are able to argue that for uncollapsed matter S <= {1/2} A.
Journal reference: JHEP 1103:056,2011
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arXiv:1012.4467
The causal structure of spacetime is a parameterized Randers geometry
Authors: Jozef Skakala (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 20 Dec 2010)
8 pages
There is a by now well-established isomorphism between stationary 4-dimensional spacetimes and 3-dimensional purely spatial Randers geometries - these Randers geometries being a particular case of the more general class of 3-dimensional Finsler geometries. We point out that in stably causal spacetimes, by using the (time-dependent) ADM decomposition, this result can be extended to general non-stationary spacetimes - the causal structure (conformal structure) of the full spacetime is completely encoded in a parameterized (time-dependent) class of Randers spaces, which can then be used to define a Fermat principle, and also to reconstruct the null cones and causal structure.
Journal reference: Class.Quant.Grav.28:065007,2011
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arXiv:1012.4806
Some generalizations of the Raychaudhuri equation
Authors: Gabriel Abreu (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 21 Dec 2010)
8 pages
The Raychaudhuri equation has seen extensive use in general relativity, most notably in the development of various singularity theorems. In this rather technical article we shall generalize the Raychaudhuri equation in several ways. First an improved version of the standard timelike Raychaudhuri equation is developed, where several key terms are lumped together as a divergence. This already has a number of interesting applications, both within the ADM formalism and elsewhere. Second, a spacelike version of the Raychaudhuri equation is briefly discussed. Third, a version of the Raychaudhuri equation is developed that does not depend on the use of normalized congruences. This leads to useful formulae for the "diagonal" part of the Ricci tensor. Fourth, a "two vector" version of the Raychaudhuri equation is developed that uses two congruences to effectively extract "off diagonal" information concerning the Ricci tensor.
Journal reference: Phys.Rev.D83:104016,2011
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arXiv:1102.2001
Elementary analysis of the special relativistic combination of velocities, Wigner rotation, and Thomas precession
Authors: Kane O'Donnell (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 9 Feb 2011 (v1), last revised 11 Jun 2011 (this version, v2))
25 pages
The purpose of this paper is to provide an elementary introduction to the qualitative and quantitative results of velocity combination in special relativity, including the Wigner rotation and Thomas precession. We utilize only the most familiar tools of special relativity, in arguments presented at three differing levels: (1) utterly elementary, which will suit a first course in relativity; (2) intermediate, to suit a second course; and (3) advanced, to suit higher level students. We then give a summary of useful results, and suggest further reading in this often obscure field.
Journal reference: European Journal of Physics 31 (2011) 1033--1047
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arXiv:1103.3013
Lower-dimensional Horava-Lifshitz gravity
Authors: Thomas P. Sotiriou, Matt Visser, Silke Weinfurtner
(Submitted on 15 Mar 2011 (v1), last revised 14 Jun 2011 (this version, v3))
9 pages
We consider Horava-Lifshitz gravity in both 1+1 and 2+1 dimensions. These lower-dimensional versions of Horava-Lifshitz gravity are simple enough to be explicitly tractable, but still complex enough to be interesting. We write the most general (non-projectable) action for each case and discuss the resulting dynamics. In the 1+1 case we utilize the equivalence with 2-dimensional Einstein-aether theory to argue that, even though non-trivial, the theory does not have any local degrees of freedom. In the 2+1 case we show that the only dynamical degree of freedom is a scalar, which qualitatively has the same dynamical behaviour as the scalar mode in (non-projectable) Horava-Lifshitz gravity in 3+1 dimensions. We discuss the suitability of these lower-dimensional theories as simpler playgrounds that could help us gain insight into the 3+1 theory. As special cases we also discuss the projectable limit of these
theories. Finally, we present an algorithm that extends the equivalence with (higher order) Einstein-aether theory to full Horava-Lifshitz gravity (instead of just the low energy limit), and we use this extension to comment on the apparent naturalness of the covariant formulation of the latter.
Journal reference: Phys.Rev.D83:124021,2011
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Status of Horava gravity: A personal perspective
Authors: Matt Visser (Victoria University of Wellington)
(Submitted on 29 Mar 2011 (v1), last revised 4 Apr 2011 (this version, v2))
11 pages
Horava gravity is a relatively recent (Jan 2009) idea in theoretical physics for trying to develop a quantum field theory of gravity. It is not a string theory, nor loop quantum gravity, but is instead a traditional quantum field theory that breaks Lorentz invariance at ultra-high (presumably trans-Planckian) energies, while retaining approximate Lorentz invariance at low and medium (sub-Planckian) energies. The challenge is to keep the Lorentz symmetry breaking controlled and small - small enough to be compatible with experiment. I will give a very general overview of what is going on in this field, paying particular attention to the disturbing role of the scalar graviton.
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arXiv:1104.1223
Comment on: Detecting Vanishing Dimensions Via Primordial Gravitational Wave Astronomy
Authors: Thomas P. Sotiriou, Matt Visser, Silke Weinfurtner
(Submitted on 7 Apr 2011)
1 page, comment to Phys. Rev. Lett. 106, 101101 (2011)
It has been recently claimed [arXiv:1102.3434] that quantum gravity models where the number of dimensions reduces at the ultraviolet exhibit a potentially observable cutoff in the primordial gravitational wave spectrum, and that this is a "generic" and "robust" test for such models, since "(2+1)-dimensional spacetimes have no gravitational degrees of freedom". We argue that such a claim is misleading.
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arXiv:1105.5646
Spectral dimension as a probe of the ultraviolet continuum regime of causal dynamical triangulations
Authors: Thomas P. Sotiriou, Matt Visser, Silke Weinfurtner
(Submitted on 27 May 2011)
5 pages, 3 figures
We explore the ultraviolet continuum regime of causal dynamical triangulations, as probed by the flow of the spectral dimension. We set up a framework in which one can find continuum theories that can fully reproduce the behaviour of the latter in this regime. In particular, we show that Horava-Lifshitz gravity can mimic the flow of the spectral dimension in causal dynamical triangulations to high accuracy and over a wide range of scales. This seems to indicate that the two theories lie in the same universality class.
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arXiv:1105.6098
From dispersion relations to spectral dimension - and back again
Authors: Thomas P. Sotiriou, Matt Visser, Silke Weinfurtner
(Submitted on 30 May 2011)
26 pages
The so-called spectral dimension is a scale-dependent number associated with both geometries and field theories that has recently attracted much attention, driven largely though not exclusively by investigations of causal dynamical triangulations (CDT) and Horava gravity as possible candidates for quantum gravity. We advocate the use of the spectral dimension as a probe for the kinematics of these (and other) systems in the region where spacetime curvature is small, and the manifold is flat to a good approximation. In particular, we show how to assign a spectral dimension (as a function of so-called diffusion time) to any arbitrarily specified dispersion relation. We also analyze the fundamental properties of spectral dimension using extensions of the usual Seeley-DeWitt and Feynman expansions, and by saddle point techniques. The spectral dimension turns out to be a useful, robust and powerful probe, not only of geometry, but also of kinematics.
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arXiv:0909.2317
Generalised superradiant scattering
Authors: Mauricio Richartz, Silke Weinfurtner, A. J. Penner, W. G. Unruh
(Submitted on 12 Sep 2009 (v1), last revised 19 Sep 2009 (this version, v2))
4 pages
We analyse the necessary and sufficient conditions for the occurrence of superradiance. Starting with a wave equation we examine the possibility of superradiance in terms of an effective potential and boundary conditions. In particular, we show that the existence of an ergoregion is not sufficient; an appropriate boundary condition, e.g. only ingoing group velocity waves at an event horizon, is also crucial. After applying our scheme to the standard examples of superradiance, we show that analogue models of gravity without an event horizon do not necessarily exhibit superradiance. Particularly, we show that the superradiant phenomenon is absent in purely rotating inviscid fluids with vorticity. We argue that there should be a catalogue of superradiant systems that can be found by focusing on the necessary and sufficient conditions outlined below.
Journal reference: Phys.Rev.D80:124016,2009
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arXiv:1008.1911
Measurement of stimulated Hawking emission in an analogue system
Authors: Silke Weinfurtner, Edmund W. Tedford, Matthew C. J. Penrice, William G. Unruh, Gregory A. Lawrence
(Submitted on 11 Aug 2010 (v1), last revised 18 Aug 2010 (this version, v2))
7 pages, 5 figures
There is a mathematical analogy between the propagation of fields in a general relativistic space-time and long (shallow water) surface waves on moving water. Hawking argued that black holes emit thermal radiation via a quantum spontaneous emission. Similar arguments predict the same effect near wave horizons in fluid flow. By placing a streamlined obstacle into an open channel flow we create a region of high velocity over the obstacle that can include wave horizons. Long waves propagating upstream towards this region are blocked and converted into short (deep water) waves. This is the analogue of the stimulated emission by a white hole (the time inverse of a black hole), and our measurements of the amplitudes of the converted waves demonstrate the thermal nature of the conversion process for this system. Given the close relationship between stimulated and spontaneous emission, our findings attest to the generality of the Hawking process.
Journal reference: Phys.Rev.Lett.106:021302,2011
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arXiv:1001.5091
The structure of boundary parameter property satisfying sets
Authors: B. E. Whale
(Submitted on 28 Jan 2010 (v1), last revised 3 May 2011 (this version, v2))
25 pages
Precise definitions of singularities in General Relativity rely on a set of curves for their mathematical definition and physical interpretation. The abstract boundary allows the set of curves to be chosen, as long as a condition called the boundary parameter property (b.p.p.) is satisfied. It is, therefore, important to determine the answer to the question, "What happens to the abstract boundary classification when we enlarge or take the union/ intersection/ complement of b.p.p. sets?" Unfortunately the standard set operations do not respect the b.p.p. In this paper we prove that there exists a correspondence between b.p.p. sets and sets of inextendible curves, modulo two conditions to do with compactness and parametrisation. Using the correspondence we are able to give meaning to the question above. In a forth coming paper will we use the results given here to answer the question above.
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arXiv:0910.0207
Post-Newtonian and Numerical Calculations of the Gravitational Self-Force for Circular Orbits in the Schwarzschild Geometry
Authors: Luc Blanchet, Steven Detweiler, Alexandre Le Tiec, Bernard F. Whiting
(Submitted on 1 Oct 2009 (v1), last revised 4 Mar 2010 (this version, v2))
36 pages, 3 figures
The problem of a compact binary system whose components move on circular orbits is addressed using two different approximation techniques in general relativity. The post-Newtonian (PN) approximation involves an expansion in powers of v/c<<1, and is most appropriate for small orbital velocities v. The perturbative self-force (SF) analysis requires an extreme mass ratio m1/m2<<1 for the components of the binary. A particular coordinate-invariant observable is determined as a function of the orbital frequency of the system using these two different approximations. The post-Newtonian calculation is pushed up to the third post-Newtonian (3PN) order. It involves the metric generated by two point particles and evaluated at the location of one of the particles. We regularize the divergent self-field of the particle by means of dimensional regularization. We show that the poles proportional to 1/(d-3) appearing
in dimensional regularization at the 3PN order cancel out from the final gauge invariant observable. The 3PN analytical result, through first order in the mass ratio, and the numerical SF calculation are found to agree well. The consistency of this cross cultural comparison confirms the soundness of both approximations in describing compact binary systems. In particular, it provides an independent test of the very different regularization procedures invoked in the two approximation schemes.
Journal reference: Phys.Rev.D81:064004,2010
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arXiv:0912.5311
Post-Newtonian Initial Data with Waves: Progress in Evolution
Authors: Bernard J. Kelly, Wolfgang Tichy, Yosef Zlochower, Manuela Campanelli, Bernard Whiting
(Submitted on 29 Dec 2009 (v1), last revised 11 May 2010 (this version, v2))
13 pages, 9 figures
In Kelly et al. [Phys. Rev. D, 76:024008, 2007], we presented new binary black-hole initial data adapted to puncture evolutions in numerical relativity. This data satisfies the constraint equations to 2.5 post-Newtonian order, and contains a transverse-traceless "wavy" metric contribution, violating the standard assumption of conformal flatness. We report on progress in evolving this data with a modern moving-puncture implementation of the BSSN equations in several numerical codes. We discuss the effect of the new metric terms on junk radiation and continuity of physical radiation extracted.
Journal reference: Class.Quant.Grav.27:114005,2010
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arXiv:1002.0726
High-Order Post-Newtonian Fit of the Gravitational Self-Force for Circular Orbits in the Schwarzschild Geometry
Authors: Luc Blanchet, Steven Detweiler, Alexandre Le Tiec, Bernard F. Whiting
(Submitted on 3 Feb 2010 (v1), last revised 12 Apr 2010 (this version, v2))
32 pages, 2 figures
We continue a previous work on the comparison between the post-Newtonian (PN) approximation and the gravitational self-force (SF) analysis of circular orbits in a Schwarzschild background. We show that the numerical SF data contain physical information corresponding to extremely high PN approximations. We find that knowing analytically determined appropriate PN parameters helps tremendously in allowing the numerical data to be used to obtain higher order PN coefficients. Using standard PN theory we compute analytically the leading 4PN and the next-to-leading 5PN logarithmic terms in the conservative part of the dynamics of a compact binary system. The numerical perturbative SF results support well the analytic PN calculations through first order in the mass ratio, and are used to accurately measure the 4PN and 5PN non-logarithmic coefficients in a particular gauge invariant observable. Furthermore we are
able to give estimates of higher order contributions up to the 7PN level. We also confirm with high precision the value of the 3PN coefficient. This interplay between PN and SF efforts is important for the synthesis of template waveforms of extreme mass ratio inspirals to be analysed by the space-based gravitational wave instrument LISA. Our work will also have an impact on efforts that combine numerical results in a quantitative analytical framework so as to generate complete inspiral waveforms for the ground-based detection of gravitational waves by instruments such as LIGO and Virgo.
Journal reference: Phys.Rev.D81:084033,2010
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arXiv:1007.2614
High-Accuracy Comparison between the Post-Newtonian and Self-Force Dynamics of Black-Hole Binaries
Authors: Luc Blanchet, Steven Detweiler, Alexandre Le Tiec, Bernard F. Whiting
(Submitted on 15 Jul 2010)
29 pages, 3 figures
The relativistic motion of a compact binary system moving in circular orbit is investigated using the post-Newtonian (PN) approximation and the perturbative self-force (SF) formalism. A particular gauge-invariant observable quantity is computed as a function of the binary's orbital frequency. The conservative effect induced by the gravitational SF is obtained numerically with high precision, and compared to the PN prediction developed to high order. The PN calculation involves the computation of the 3PN regularized metric at the location of the particle. Its divergent self-field is regularized by means of dimensional regularization. The poles proportional to 1/(d-3) which occur within dimensional regularization at the 3PN order disappear from the final gauge-invariant result. The leading 4PN and next-to-leading 5PN conservative logarithmic contributions originating from gravitational-wave tails are also obtained. Making use
of these exact PN results, some previously unknown PN coefficients are measured up to the very high 7PN order by fitting to the numerical self-force data. Using just the 2PN and new logarithmic terms, the value of the 3PN coefficient is also confirmed numerically with very high precision. The consistency of this cross-cultural comparison provides a crucial test of the very different regularization methods used in both SF and PN formalisms, and illustrates the complementarity of these approximation schemes when modelling compact binary systems.
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arXiv:1012.2150
Long gravitational-wave transients and associated detection strategies for a network of terrestrial interferometers
Authors: Eric Thrane, Shivaraj Kandhasamy, Christian D Ott, Warren G Anderson, Nelson L Christensen, Michael W Coughlin, Steven Dorsher, Stefanos Giampanis, Vuk Mandic, Antonis Mytidis, Tanner Prestegard, Peter Raffai, Bernard Whiting
(Submitted on 10 Dec 2010 (v1), last revised 25 Feb 2011 (this version, v3))
Searches for gravitational waves (GWs) traditionally focus on persistent sources (e.g., pulsars or the stochastic background) or on transients sources (e.g., compact binary inspirals or core-collapse supernovae), which last for timescales of milliseconds to seconds. We explore the possibility of long GW transients with unknown waveforms lasting from many seconds to weeks. We propose a novel analysis technique to bridge the gap between short O(s) burst analyses and persistent stochastic analyses. Our technique utilizes frequency-time maps of GW strain cross-power between two spatially separated terrestrial GW detectors. The application of our cross-power statistic to searches for GW transients is framed as a pattern recognition problem, and we discuss several pattern-recognition techniques. We demonstrate these techniques by recovering simulated GW signals in simulated detector noise. We also recover environmental noise
artifacts, thereby demonstrating a novel technique for the identification of such artifacts in GW interferometers. We compare the efficiency of this framework to other techniques such as matched filtering.
Journal reference: Phys.Rev.D83:083004,2011
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arXiv:0909.0749
Average observational quantities in the timescape cosmology
Authors: David L. Wiltshire
(Submitted on 4 Sep 2009 (v1), last revised 11 Dec 2009 (this version, v2))
22 pages, 12 figures
We examine the properties of a recently proposed observationally viable alternative to homogeneous cosmology with smooth dark energy, the timescape cosmology. In the timescape model cosmic acceleration is realized as an apparent effect related to the calibration of clocks and rods of observers in bound systems relative to volume-average observers in an inhomogeneous geometry in ordinary general relativity. The model is based on an exact solution to a Buchert average of the Einstein equations with backreaction. The present paper examines a number of observational tests which will enable the timescape model to be distinguished from homogeneous cosmologies with a cosmological constant or other smooth dark energy, in current and future generations of dark energy experiments. Predictions are presented for: comoving distance measures; H(z); the equivalent of the dark energy equation of state, w(z); the Om(z) measure of Sahni,
Shafieloo and Starobinsky; the Alcock-Paczynski test; the baryon acoustic oscillation measure, D_v; the inhomogeneity test of Clarkson, Bassett and Lu; and the time drift of cosmological redshifts. Where possible, the predictions are compared to recent independent studies of similar measures in homogeneous cosmologies with dark energy. Three separate tests with indications of results in possible tension with the Lambda CDM model are found to be consistent with the expectations of the timescape cosmology.
Journal reference: Phys.Rev.D80:123512,2009
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arXiv:0912.4563
From time to timescape - Einstein's unfinished revolution
Authors: David L. Wiltshire
(Submitted on 23 Dec 2009)
13 pages, 3 figures
I argue that Einstein overlooked an important aspect of the relativity of time in never quite realizing his quest to embody Mach's principle in his theory of gravity. As a step towards that goal, I broaden the Strong Equivalence Principle to a new principle of physics, the Cosmological Equivalence Principle, to account for the role of the evolving average regional density of the universe in the synchronisation of clocks and the relative calibration of inertial frames. In a universe dominated by voids of the size observed in large-scale structure surveys, the density contrasts of expanding regions are strong enough that a relative deceleration of the background between voids and the environment of galaxies, typically of order 10^{-10} m/s^2, must be accounted for. As a result one finds a universe whose present age varies by billions of years according to the position of the observer: a timescape. This model
universe is observationally viable: it passes three critical independent tests, and makes additional predictions. Dark energy is revealed as a mis-identification of gravitational energy gradients and the resulting variance in clock rates. Understanding the biggest mystery in cosmology therefore involves a paradigm shift, but in an unexpected direction: the conceptual understanding of time and energy in Einstein's own theory is incomplete.
Journal reference: Int.J.Mod.Phys.D18:2121-2134,2009
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arXiv:0912.5234
Gravitational energy as dark energy: Towards concordance cosmology without Lambda
Authors: David L. Wiltshire
(Submitted on 29 Dec 2009)
8 pages, 1 figure
I briefly outline a new physical interpretation to the average cosmological parameters for an inhomogeneous universe with backreaction. The variance in local geometry and gravitational energy between ideal isotropic observers in bound structures and isotropic observers at the volume average location in voids plays a crucial role. Fits of a model universe to observational data suggest the possibility of a new concordance cosmology, in which dark energy is revealed as a mis-identification of gravitational energy gradients that become important when voids grow at late epochs.
Journal reference: EAS Publ.Ser.36:91-98,2009
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arXiv:0912.5236
Gravitational energy as dark energy: Average observational quantities
Authors: David L. Wiltshire
(Submitted on 29 Dec 2009)
10 pages, 7 figures
In the timescape scenario cosmic acceleration is understand as an apparent effect, due to gravitational energy gradients that grow when spatial curvature gradients become significant with the nonlinear growth of cosmic structure. This affects the calibratation of local geometry to the solutions of the volume-average evolution equations corrected by backreaction. In this paper I discuss recent work on defining observational tests for average geometric quantities which can distinguish the timescape model from a cosmological constant or other models of dark energy.
Journal reference: AIP Conf.Proc.1241:1182-1191,2010
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arXiv:1102.2045
Gravitational energy as dark energy: Cosmic structure and apparent acceleration
Authors: David L. Wiltshire
(Submitted on 10 Feb 2011)
24 pages, 14 figures
Below scales of about 100/h Mpc our universe displays a complex inhomogeneous structure dominated by voids, with clusters of galaxies in sheets and filaments. The coincidence that cosmic expansion appears to start accelerating at the epoch when such structures form has prompted a number of researchers to question whether dark energy is a signature of a failure of the standard cosmology to properly account, on average, for the distribution of matter we observe. Here I discuss the timescape scenario, in which cosmic acceleration is understood as an apparent effect, due to gravitational energy gradients that grow when spatial curvature gradients become significant with the nonlinear growth of cosmic structure. I discuss conceptual issues related to the averaging problem, and their impact on the calibration of local geometry to the solutions of the volume-average evolution equations corrected by backreaction, and the question of
nonbaryonic dark matter in the timescape framework. I further discuss recent work on defining observational tests for average geometric quantities which can distinguish the timescape model from a cosmological constant or other models of dark energy.
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arXiv:1106.1693
What is dust? - Physical foundations of the averaging problem in cosmology
Authors: David L. Wiltshire
(Submitted on 9 Jun 2011)
39 pages, 3 figures, accepted by Classical and Quantum Gravity for the special issue "Inhomogeneous Cosmological Models and Averaging in Cosmology"
Abstract: The problems of coarse-graining and averaging of inhomogeneous cosmologies, and their backreaction on average cosmic evolution, are reviewed from a physical viewpoint. A particular focus is placed on comparing different notions of average spatial homogeneity, and on the interpretation of observational results. Among the physical questions we consider are: the nature of an average Copernican principle, the role of Mach's principle, the issue of quasilocal gravitational energy and the different roles of spacetime, spatial and null cone averages. The observational interpretation of the timescape scenario is compared to other approaches to cosmological averaging, and outstanding questions are discussed.
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arXiv:1002.0648
Neutrino oscillations in Kerr-Newman space-time
Authors: Jun Ren, Cheng-Min Zhang
(Submitted on 3 Feb 2010)
20 pages
The mass neutrino oscillation in Kerr-Newman(K-N) space-time is studied in the plane $\theta=\theta_{0}$, and the general equations of oscillation phases are given. The effect of the rotation and electric charge on the phase is presented. Then, we consider three special cases: (1) The neutrinos travel along the geodesics with the angular momentum $L=aE$ in the equatorial plane. (2) The neutrinos travel along the geodesics with L=0 in the equatorial plane. (3) The neutrinos travel along the radial geodesics at the direction $\theta=0$. At last, we calculate the proper oscillation length in the K-N space time. The effect of the gravitational field on the oscillation length is embodied in the gravitational red shift factor. When the neutrino travels out of the gravitational field, the blue shift of the oscillation length takes place. We discussed the variation of the oscillation length influenced by the gravitational field strength, the rotation $a^{2}$ and charge $Q$.
Journal reference: Class. Quantum Grav. 27: 065011,2010
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arXiv:0901.1439
Thermodynamics of Spinor Quintom
Authors: Jing Wang, Shu-wang Cui, Cheng-min Zhang
(Submitted on 11 Jan 2009 (v1), last revised 24 Nov 2010 (this version, v2))
8 pages
We discuss the thermodynamic properties of dark energy (DE) with Quintom matter in spinor scenario. (1).Using the Cardy-Verlinde formula, we investigate the conditions of validity of the Generalized Second Law of thermodynamics (GSL) in the four evolutionary phases of Spinor Quintom-B model. We also clarify its relation with three cosmological entropy bounds. (2). We take thermodynamic stability of the combination between Spinor Quintom DE and the generalized Chaplygin Gas (GCG) perfect fluid into account, and we find that in the case of $\beta>0$ and $010^{44} erg which is comparable to the giant flares. We find no evidence of GWs associated with a sample of 1279 electromagnetic triggers from six
magnetars occurring between November 2006 and June 2009, in GW data from the LIGO, Virgo, and GEO600 detectors. Our lowest model-dependent GW emission energy upper limits for band- and time-limited white noise bursts in the detector sensitive band, and for f-mode ringdowns (at 1090 Hz), are 3.0x10^{44} d_1^2 erg and 1.4x10^{47} d_1^2 erg respectively, where d_1 = d_{0501} / 1 kpc and d_{0501} is the distance to SGR 0501+4516. These limits on GW emission from f-modes are an order of magnitude lower than any previous, and approach the range of electromagnetic energies seen in SGR giant flares for the first time.
Journal reference: 2011 ApJ 734 L35
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arXiv:1102.3781
Search for gravitational waves from binary black hole inspiral, merger and ringdown
Authors: The LIGO Scientific Collaboration, the Virgo Collaboration: J. Abadie, B. P. Abbott, R. Abbott, M. Abernathy, T. Accadia, F. Acernese, C. Adams, R. Adhikari, P. Ajith, B. Allen, G. S. Allen, E. Amador Ceron, R. S. Amin, S. B. Anderson, W. G. Anderson, F. Antonucci, M. A. Arain, M. C. Araya, M. Aronsson, Y. Aso, S. M. Aston, P. Astone, D. Atkinson, P. Aufmuth, C. Aulbert, S. Babak, P. Baker, G. Ballardin, T. Ballinger, S. Ballmer, D. Barker, S. Barnum, F. Barone, B. Barr, P. Barriga, L. Barsotti, M. Barsuglia, M. A. Barton, I. Bartos, R. Bassiri, M. Bastarrika, J. Bauchrowitz, Th. S. Bauer, B. Behnke, M.G. Beker, A. Belletoile, M. Benacquista, A. Bertolini, J. Betzwieser, N. Beveridge, P. T. Beyersdorf, I. A. Bilenko, G. Billingsley, J. Birch, S. Birindelli, R. Biswas, M. Bitossi, M. A. Bizouard, et al. (664 additional authors not shown)
(Submitted on 18 Feb 2011)
19 pages, 3 figures
We present the first modeled search for gravitational waves using the complete binary black hole gravitational waveform from inspiral through the merger and ringdown for binaries with negligible component spin. We searched approximately 2 years of LIGO data taken between November 2005 and September 2007 for systems with component masses of 1-99 solar masses and total masses of 25-100 solar masses. We did not detect any plausible gravitational-wave signals but we do place upper limits on the merger rate of binary black holes as a function of the component masses in this range. We constrain the rate of mergers for binary black hole systems with component masses between 19 and 28 solar masses and negligible spin to be no more than 2.0 per Mpc^3 per Myr at 90% confidence.
Journal reference: Phys.Rev.D83:122005,2011
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arXiv:1104.2712
Beating the spin-down limit on gravitational wave emission from the Vela pulsar
Authors: The LIGO Scientific Collaboration, the Virgo Collaboration: J. Abadie, B. P. Abbott, R. Abbott, M. Abernathy, T. Accadia, F. Acernese, C. Adams, R. Adhikari, C. Affeldt, B. Allen, G. S. Allen, E. Amador Ceron, D. Amariutei, R. S. Amin, S. B. Anderson, W. G. Anderson, F. Antonucci, K. Arai, M. A. Arain, M. C. Araya, S. M. Aston, P. Astone, D. Atkinson, P. Aufmuth, C. Aulbert, B. E. Aylott, S. Babak, P. Baker, G. Ballardin, S. Ballmer, D. Barker, S. Barnum, F. Barone, B. Barr, P. Barriga, L. Barsotti, M. Barsuglia, M. A. Barton, I. Bartos, R. Bassiri, M. Bastarrika, A. Basti, J. Bauchrowitz, Th. S. Bauer, B. Behnke, M. Bejger, M.G. Beker, A. S. Bell, A. Belletoile, I. Belopolski, M. Benacquista, A. Bertolini, J. Betzwieser, N. Beveridge, P. T. Beyersdorf, I. A. Bilenko, G. Billingsley, J. Birch, et al. (690 additional authors not shown)
(Submitted on 14 Apr 2011 (v1), last revised 15 Apr 2011 (this version, v2))
37 pages, 6 figures
We present direct upper limits on continuous gravitational wave emission from the Vela pulsar using data from the Virgo detector's second science run. These upper limits have been obtained using three independent methods that assume the gravitational wave emission follows the radio timing. Two of the methods produce frequentist upper limits for an assumed known orientation of the star's spin axis and value of the wave polarization angle of, respectively, $1.9\ee{-24}$ and $2.2\ee{-24}$, with 95% confidence. The third method, under the same hypothesis, produces a Bayesian upper limit of $2.1\ee{-24}$, with 95% degree of belief. These limits are below the indirect {\it spin-down limit} of $3.3\ee{-24}$ for the Vela pulsar, defined by the energy loss rate inferred from observed decrease in Vela's spin frequency, and correspond to a limit on the star ellipticity of $\sim 10^{-3}$. Slightly less stringent results, but still
well below the spin-down limit, are obtained assuming the star's spin axis inclination and the wave polarization angles are unknown.
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