Subject: ASGRG Newsletter #17
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AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION
Electronic Newsletter -- #17, 2007
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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 31 October, 2008.
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CONTENTS:
* REPORT ON 18TH INTERNATIONAL CONFERENCE ON GENERAL RELATIVITY
AND GRAVITATION (GRG18)
* MINUTES OF THE 5TH BIENNIAL GENERAL MEETING OF THE ASGRG
12 July 2007
* MEMBERSHIP DETAILS ONLINE at
http://www.physics.adelaide.edu.au/ASGRG/members.html
* SUBSCRIPTIONS
* FORTHCOMING MEETINGS
* MEMBERS' ABSTRACTS at gr-qc, December 2006 - November 2007
* ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc,
December 2006 - November 2007
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Report on 18th International Conference
on General Relativity and Gravitation (GRG18)
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GRG18: DARLING HARBOUR, SYDNEY, 8-13 JULY 2007
The 18th International Conference on General Relativity and Gravitation
(GRG18) was held at the Sydney Convention and Exhibition Centre,
Darling Harbour, Sydney, Australia from 8 to 13 July 2007. GRG18 was
the 18th in a series of conferences on general relativity and
gravitation that are held every three years under the auspices of the
International Society for General Relativity and Gravitation (ISGRG).
The Local Organising Committee for the conference consisted of members
of the ASGRG Executive Committee, plus some co-opted ASGRG members.
Susan Scott was the Chair of the LOC, David Mclelland was the
Deputy Chair, and John Steele the Treasurer. The remaining LOC members
were David Wiltshire, Peter Veitch, Li Ju, Leo Brewin and Malcolm
Anderson. The Chair of the Scientific Organising Committe was B.S.
Sathyaprakash of Cardiff University.
The principal sub-themes of the conference were:
* experimental tests of general relativity,
* alternative theories of gravity,
* analogue gravity,
* exact solutions of Einstein’s field equations,
* mathematical aspects of the field equations,
* numerical relativity,
* twistor theory,
* theories of quantum gravity,
* quantum aspects of black holes,
* relativistic astrophysics,
* gravitational wave sources and detection,
* the early universe,
* dark energy, and
* quantum cosmology.
A total of 360 papers were due to be presented during the parallel
sessions at GRG18, and in addition there were 15 plenary lectures
lasting an hour each, and two public lectures. The speakers were
drawn from 37 countries around the world, including Australia, New
Zealand, Britain, the United States, China, India, Russia, Japan,
Brazil, Germany, France, Italy, Spain, Singapore, Taiwan, South
Korea and Iran.
The 15 plenary speakers were:
* Stanley Whitcomb of the California Institute of Technology,
who spoke about "Ground-Based Gravitational Wave Detection",
* Laurent Friedel of the Perimeter Institute of Theoretical
Physics, Ontario, who spoke about "Spin-Foam Models of the Dynamics of
Quantum Space Time",
* Steve McMillan of Drexel University, Philadelphia, who spoke about
"Gravitational Dynamics of Large Stellar Systems",
* Badri Krishnan of the Max Planck Institute for Gravitational
Physics, Germany, who spoke about "Quasi-Local Black Hole Horizons and
Their Applications",
* Bernd Bruegman of Friedrich-Schiller-University, Germany, who spoke
about "Numerical Relativity",
* Daniel Eisenstein of the University of Arizona, who spoke about
"Observing Dark Energy",
* Peter Schneider of the Argelander Institute for Astronomy, Germany,
who spoke about "Cosmological Probes for Gravitational Lensing",
* Renate Loll of Utrecht University, the Netherlands, who spoke on
"The Emergence of Spacetime, or Quantum Gravity on Your Desktop",
* Francis Everitt of Stanford University, who spoke about "Testing
Einstein in Space: Gravity Probe B and STEP",
* Hans Ringstrom of KTH Stockholm, who spoke about "Cosmic Censorship",
* Joanthan Feng of the University of California, who spoke about
"Collider Physics and Cosmology",
* Daniel Shaddock of the California Institute of Technology, who spoke
about "Space-Based Gravitational Wave Detection with LISA",
* Maria Alessandra Papa of the University of Wisconsin, who spoke about
"Gravitational Wave Astronomy from Ground and Space",
* Robert Myers of the Perimeter Institute of Theoretical Physics,
Ontario, who spoke about "Quark Soup Al Dente: Applied String Theory", and
* Ralph Schuetzhold of Dresden University of Technology, Germany, who
spoke about "Effective Horizons in the Laboratory".
The two public speakers were Kip Thorne, who gave a talk on gravitational
waves and the various methods proposed or already implemented for detecting
them, and Roger Penrose, who outlined a cyclic cosmological model in which
a thermalised late-universe phase spontaneously transitions into the next
hot Big Bang.
Although the weather in Sydney during the week of GRG18 was mostly cold,
overcast and drizzly, the conference venue was ideally located with easy
access to Darling Harbour's many fine restaurants and other attractions.
The conference banquet, on the evening of Wednesday July 11, was enjoyed
on board a harbour cruise.
GRG18 was run in conjunction with the 7th Eduardo Amaldi Conference on
Gravitational Waves, and the two events shared the same programme for
most of the week, with Amaldi7 holding an extra day of talks on Saturday
July 14.
Overall, GRG18 and Amaldi7 were very stimulating events, and a lot of fun.
Their success was a fitting testimony to the tireless efforts of Sue Scott
and her team. (I can say this without the risk of appearing immodest, as
my own role in the LOC was a purely nominal one.)
Malcolm Anderson
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MINUTES OF THE 5TH BIENNIAL GENERAL MEETING OF THE ASGRG
held at Sydney Convention and Exhibition Centre, Darling Harbour,
Sydney, 12 July, 2007
The meeting opened at 1.15 p.m.
[14 people were present, but only 12 of them were ASGRG members. Since the
total number of ASGRG members registered for GRG18 was 15, the BGM was
quorate: the Constitution (item 18 (i)) specifies the quorum for a General
Meeting as "one quarter of the members present at the Conference."]
Apologies: David Blair, Peter Veitch
1. The minutes of the 4th Biennial General Meeting, held at Monash
University, 8 January 2004, were presented to the meeting. John Schutz
moved that the minutes be accepted, and Bernard Whiting seconded. The motion
was approved.
2. Remote Ballot: Leo Brewin reported that the Remote Ballot held for the
purpose of regularising the BGM by (a) cancelling the biennial Conference
of the Society which was to have been held in Christchurch in January 2006
[as mandated by item 15 (i) of the Constitution], and (b) declaring GRG18 a
Conference of the Society as required by item 16 (i), had been passed with
10 votes in favour and none against.
3. President's Report: According to Susan Scott, the Society had been
"incredibly active" since the last meeting at Monash University in January
2004. Most notably, the Committe made a renewed bid at GRG17 in Dublin in
July 2004 to hold the next conference in the GRG series, and of course was
successful. ASGRG Committee members formed much of the Local Organising
Committee for the resulting conference, GRG18.
Other activities of Committee members included the organisation
of the "Kerr Fest" at the University of Canterbury in August 2004. Sue
mentioned that the proceedings of this meeting would be published soon.
Another promising development was the launch of the prospectus for
the Australian International Gravitational Observatory (AIGO) in 2006.
On a less positive note, membership of ASGRG seemed to be shrinking.
Sue urged all members to encourage their students and post-docs, to join the
Society.
Finally, Sue made mention of a change in Committee personnel. Antony
Searle resigned as Treasurer of the ASGRG in November 2005, and was replaced
by John Steele, who was co-opted onto the Committee for that purpose.
The Meeting voted to extend the thanks of the Society to Susan Scott,
David McClelland and John Steele for all their efforts in relation to GRG18.
4. Treasurer's Report: John Steele reported that the current financial
membership of the ASGRG was 47. In the period since the Monash meeting in
January 2004 7 new members had joined and 42 had resigned.
The Society's funds had increased from $12,206 in November 2003
to $17,784 in July 2007. The main source of income was the proceeds of life
membership, although ACGRG4 at Monash also contributed to the Society's
coffers by making a profit of $1850. The main expenses were bank fees, and
John has asked the Commonwealth Bank for a review of these fees. It was
suggested that the Society put 3/4 of its reserves into an interest-bearing
account, but John pointed out that it was very difficult for the Society
to change either banks or accounts.
5. Auditor's Report: The Auditor, John Schutz, stated that he was
satisfied with the Society's accounts and had signed a letter to
that effect.
6. Appointment of Auditor for the next session: John Schutz agreed to
remain the Auditor of the Society's accounts. David Wiltshire
proposed the reappointment and Leo Brewin seconded. The reappointment
was approved.
7. Date and venue for ACGRG5: The meeting decided that ACGRG5 would be held
at the University of Canterbury, Christchurch, in February 2010.
8. Election of officers: The following people were elected officers of
the ASGRG Committee by acclamation:
President: Susan Scott
Treasurer: John Steele
Secretary: Malcolm Anderson
Officer: David Wiltshire
Officer: Bram Slagmolen
Officer: Matt Visser (co-opted)
(The first four positions were reappointments. The last two were proposed
by David Wiltshire and seconded by Susan Scott.)
9. Square Kilometre Array (SKA). Matt Visser suggested that the ASGRG
offer public support for the Australian/NZ bid for the SKA, planned to
be the world's biggest radio telescope. David McClelland pointed out
in response that the SKA was competing for funds with the AIGO, and in
any case public statements from the ASGRG carry no weight. The Meeting
decided that the Society will take no position on the SKA.
10. Underwriting GRG18. Susan Scott asked if the Society was willing to
cover potential losses incurred by GRG18. She explained that the Australian
Institute of Physics was already covering GRG18's losses to a limit of
$20,000, and requested a contribution from the ASGRG if the losses exceeded
this sum. Bernard Whiting propOsed that the Society provide additional
cover up to a limit of $5,000. Leo Brewin seconded the proposal, and it was
passed unanimously (with 12 votes for).
The meeting closed at 2.20 p.m.
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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 2008 - June 2009 subscriptions are requested, if you wish to
pay for July 2009 - June 2010 at the same time, it may simplify matters.
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FORTHCOMING MEETINGS
December 17-21, 2007: 6th International Conference on Gravitation and Cosmology (ICGC-07)
IUCAA, Pune, India
http://meghnad.iucaa.ernet.in/~icgc07/index.html
January 7-12, 2008: Non-Perturbative Gauge Theories and Gravity
S.N. Bose National Centre for Basic Sciences, Kolkata, India
http://www.bose.res.in/~qgt08/
January 24-29, 2008: APCTP Winter School on Black Hole Astrophysics 2008
"Computational Methods in Black Hole Physics and High Energy
Astrophysics around Black Holes"
KASI, Daejeon and APCTP, Pohang, South Korea
http://numerics.inje.ac.kr/symposium/bh2008/
January 31 - February 1, 2008: Southern African Relativity Society Conference
University of Cape Town, South Africa
http://cosmology.uct.ac.za/sars/
March 7-8, 2008: Fourth Gulf Coast Gravity Meeting
University of Mississippi, Oxford MS, USA
http://www.phy.olemiss.edu/GR/gcgm4/
March 18-19, 2008: 8th British Gravitational Conference (Britgrav8)
University of York, UK
http://maths.york.ac.uk/www/BritGrav8
March 21-22, 2008: 24th West Coast Gravity Meeting
Kavli Institute for Theoretical Physics, University of California, Santa Barbara
http://www.physics.ucsb.edu/~relativity/24thPCGM.html
June 16-20, 2008: 7th International LISA Symposium
CosmoCaixa, Barcelona, Spain
http://www.ice.cat/research/LISA_Symposium
June 23-28, 2008: 13th Russian International Conference on Gravitation, Cosmology and Astrophysics (RUSGRAV-13)
PFUR, Moscow, Russia
http://www.com2com.ru/rgs/conf12.htm
June 27 - July 5, 2008: 2nd Course of the International School on Astrophysical Relativity
"Frontiers in Numerical Gravitational Astrophysics"
EMFCSC, Erice, Italy
http://astro1.phys.uniroma1.it/ericeschool/index.html
June 30 - July 4, 2008: QG^2 - Quantum Geometry and Quantum Gravity Conference
University of Nottingham, UK
http://www.maths.nottingham.ac.uk/conferences/qgsquared-2008/
July 8-14, 2007: 7th Alexander Friedmann International Seminar on Gravitation and Cosmology
Joao Pessoa, Brazil
http://www.fisica.ufpb.br/eventos/friedmann2008/friedmann2008new2.htm
August 25-29, 2008: Conference on Geometry and Analysis
Royal Institute of Technology, Stockholm, Sweden
http://www.math.kth.se/ag08/
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MEMBERS' ABSTRACTS at gr-qc, December 2006 - November 2007
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.
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arXiv:0708.1810
1+1+2 Electromagnetic perturbations on non-vacuum LRS class II space-times:
Decoupling scalar and 2-vector harmonic amplitudes
Authors: R B Burston
(Submitted on 14 Aug 2007)
9 pages
We use the covariant and gauge-invariant 1+1+2 formalism of Clarkson and
Barrett \cite{Clarkson2003} to analyze electromagnetic (EM) perturbations
on non-vacuum {\it locally rotationally symmetric} (LRS) class II
space-times. Ultimately, we show how to derive six real decoupled equations
governing the total of six EM scalar and 2-vector harmonic amplitudes. Four
of these are new, and result from expanding the complex EM 2-vector which
we defined in \cite{Burston2007} in terms of EM 2-vector harmonic amplitudes.
We are then able to show that there are four precise combinations of the
amplitudes that decouple, two of these are polar perturbations whereas the
remaining two are axial. The remaining two decoupled equations are the
generalized Regge-Wheeler equations which were developed previously in
\cite{Betschart2004}, and these govern the two EM scalar harmonic amplitudes.
However, our analysis generalizes this by including a full description and
classification of energy-momentum sources, such as charges and currents.
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arXiv:0708.1811
1+1+2 Electromagnetic perturbations on general LRS space-times: Regge-Wheeler
and Bardeen-Press equations
Authors: R. B. Burston, A. W. C. Lun
(Submitted on 14 Aug 2007)
We use the, covariant and gauge-invariant, 1+1+2 formalism developed by
Clarkson and Barrett, and develop new techniques, to decouple electromagnetic
(EM) perturbations on arbitrary locally rotationally symmetric (LRS)
space-times. Ultimately, we derive 3 decoupled complex equations governing 3
complex scalars. One of these is a new Regge-Wheeler (RW) equation
generalized for LRS space-times, whereas the remaining two are new
generalizations of the Bardeen-Press (BP) equations. This is achieved by
first using linear algebra techniques to rewrite the first-order Maxwell
equations in a new complex 1+1+2 form which is conducive to decoupling. This
new complex system immediately yields the generalized RW equation, and
furthermore, we also derive a decoupled equation governing a newly defined
complex EM 2-vector. Subsequently, a further decomposition of the 1+1+2
formalism into a 1+1+1+1 formalism is developed, allowing us to decompose the
complex EM 2-vector, and its governing equations, into spin-weighted scalars,
giving rise to the generalized BP equations.
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arXiv:0708.1812
1+1+2 gravitational perturbations on LRS class II space-times: Decoupling
GEM tensor harmonic amplitudes
Authors: R. B. Burston
(Submitted on 14 Aug 2007)
This paper considers gauge-invariant and covariant gravitational
perturbations on arbitrary vacuum locally rotationally symmetric (LRS) class
II space-times. Ultimately, we derive four decoupled equations governing
four specific combinations of the gravito-electromagnetic (GEM) 2-tensor
harmonic amplitudes. We use the gauge-invariant and covariant 1+1+2 formalism
which Clarkson and Barrett developed for analysis of vacuum Schwarzschild
perturbations. In particular we focus on the first-order 1+1+2 GEM system and
use linear algebra techniques suitable for exploiting its structure.
Consequently, we express the GEM system new 1+1+2 complex form by choosing
new complex GEM tensors, which is conducive to decoupling. We then show how
to derive a gauge-invariant and covariant decoupled equation governing a
newly defined complex GEM 2-tensor. Finally, the GEM 2-tensor is expanded in
terms of arbitrary tensor harmonics and linear algebra is used once again to
decouple the system further into 4 real decoupled equations.
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arXiv:0708.2558
1+1+2 gravitational perturbations on LRS class II space-times: GEM vector
harmonic amplitudes
Authors: R. B. Burston
(Submitted on 19 Aug 2007)
This is the second in a series of papers which considers first-order
gauge-invariant and covariant gravitational perturbations to locally
rotationally symmetric (LRS) class II space-times. This paper shows how to
decouple a complex combination of the gravito-electromagnetic (GEM)
2-vectors with the 2-tensors describing the shear of the 2/3-sheets. An
arbitrary harmonic expansion is then used along with an eigen-vector/value
analysis of the first-order GEM system, analogous to the first paper in
this series. This results in four real decoupled equations governing four
real combinations of the harmonic amplitudes of the GEM 2-vectors and the
(2/3-sheet) shear 2-tensors. Finally, these are categorized into polar and
axial perturbations.
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arXiv:0708.2559
1+1+2 gravitational perturbations on LRS class II space-times: GEM scalar
harmonic amplitudes
Authors: R. B. Burston
(Submitted on 19 Aug 2007)
This is the third in a series of papers which considers first-order
gauge-invariant and covariant gravitational perturbations to locally
rotationally symmetric (LRS) class II space-times. In this paper we complete
our analysis of the first-order gravito-electromagnetic (GEM) system by
showing how to derive three decoupled equations governing the GEM scalar
fields. One of these is for the gravito-magnetic scalar, whereas another two
arise from the 2-gradient of the gravito-electric scalar.
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arXiv:0704.3372
Shearfree perfect fluids with solenoidal magnetic curvature and a gamma-law
equation of state
Authors: Norbert Van den Bergh, John Carminati, Hamid Reza Karimian
(Submitted on 25 Apr 2007)
11 pages
We show that shearfree perfect fluids obeying an equation of state
p=(gamma-1)mu are non-rotating or non-expanding under the assumption that
the spatial divergence of the magnetic part of the Weyl tensor is zero.
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arXiv:0710.3543
The significance of numerical coincidences in nature
Authors: Brandon Carter
(Submitted on 18 Oct 2007)
This is the first part of a survey whose ultimate purpose is to clarify the
significance of the famous coincidence between the Hubble age of the
universe and a certain combination of microphysical parameters. In this part
the way is prepared by a discussion of the manner in which familiar local
phenomena depend qualitatively, and in order of magnitude, quantitatively on
the fundamental parameters of microphysics. In order to keep the account
concise while remaining self contained, only the barest essentials of the
standard nuclear physical and astrophysical calculations involved are given.
Only six of the fundamental parameters play a dominant part, namely the
coupling constants of the strong, electromagnetic, and gravitational forces,
and the mass ratios of the proton, neutron, electron and pi-meson. Attention
is drawn to the important consequences of three coincidental relationships
between these parameters. It is shown that most of the principle limiting
masses of astrophysics arise (in fundamental units) simply as the reciprocal
of the gravitational fine structure constant, with relatively small
adjustment factors. The dividing point between red dwarf and blue giant
stars turns out to be an exception: this division occurs within the range of
the main sequence stars only as a consequence of the rather exotic
coincidence that the ninth power of the electromagnetic fine structure
constant is roughly equal to the square root of the gravitational fine
structure constant.
Comments: 73 latex pages, consisting of 5 page postscript appended to
transcript (with original figures by photocopy) of 68 page manuscript
printed by stencil in 1967 under subheading "The role of fundamental
microphysical parameters in cosmogony", as a foundation for what was to
become known as the anthropic principle.
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arXiv:gr-qc/0612091
The Search for Massive Black Hole Binaries with LISA
Authors: Neil J. Cornish, Edward K. Porter
(Submitted on 14 Dec 2006 (v1), last revised 15 Nov 2007 (this version, v3))
In this work we focus on the search and detection of Massive black hole
binary (MBHB) systems, including systems at high redshift. As well as
expanding on previous works where we used a variant of Markov Chain Monte
Carlo (MCMC), called Metropolis-Hastings Monte Carlo, with simulated
annealing, we introduce a new search method based on frequency annealing
which leads to a more rapid and robust detection. We compare the two
search methods on systems where we do and do not see the merger of the
black holes. In the non-merger case, we also examine the posterior
distribution exploration using a 7-D MCMC algorithm. We demonstrate that
this method is effective in dealing with the high correlations between
parameters, has a higher acceptance rate than previously proposed methods
and produces posterior distribution functions that are close to the
prediction from the Fisher Information matrix. Finally, after carrying out
searches where there is only one binary in the data stream, we examine the
case where two black hole binaries are present in the same data stream. We
demonstrate that our search algorithm can accurately recover both binaries,
and more importantly showing that we can safely extract the MBHB sources
without contaminating the rest of the data stream.
Comments: Final published version. Accepted by Classical and Quantum Gravity
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arXiv:gr-qc/0701167
Searching for Massive Black Hole Binaries in the first Mock LISA Data
Challenge
Authors: Neil J. Cornish, Edward K. Porter
(Submitted on 30 Jan 2007)
The Mock LISA Data Challenge is a worldwide effort to solve the LISA data
analysis problem. We present here our results for the Massive Black Hole
Binary (BBH) section of Round 1. Our results cover Challenge 1.2.1, where
the coalescence of the binary is seen, and Challenge 1.2.2, where the
coalescence occurs after the simulated observational period. The data
stream is composed of Gaussian instrumental noise plus an unknown BBH
waveform. Our search algorithm is based on a variant of the Markov Chain
Monte Carlo method that uses Metropolis-Hastings sampling and
thermostated frequency annealing. We present results from the training
data sets and the blind data sets. We demonstrate that our algorithm is
able to rapidly locate the sources, accurately recover the source
parameters, and provide error estimates for the recovered parameters.
Comments: 11 pages, 6 figures, Submitted to CQG proceedings of GWDAW 11,
AEI, Germany, Dec 2006
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arXiv:gr-qc/0701170
An overview of the second round of the Mock LISA Data Challenges
Authors: K A Arnaud, S Babak, J G Baker, M J Benacquista, N J Cornish,
C Cutler, L S Finn, S L Larson, T Littenberg, E K Porter, M Vallisneri,
A Vecchio, J-Y Vinet (the Mock LISA Data Challenge Task Force)
(Submitted on 30 Jan 2007 (v1), last revised 16 Nov 2007 (this version, v4))
The Mock Data Challenges (MLDCs) have the dual purpose of fostering the
development of LISA data-analysis tools and capabilities and of demonstrating
the technical readiness already achieved by the gravitational-wave community
in distilling a rich science payoff from the LISA data. The first round of
MLDCs has just been completed and the second-round data sets are being
released shortly after this workshop. The second-round data sets contain
radiation from an entire Galactic population of stellar-mass binary systems,
from massive--black-hole binaries, and from extreme--mass-ratio inspirals.
These data sets are designed to capture much of the complexity that is
expected in the actual LISA data, and should provide a fairly realistic
setting to test advanced data-analysis techniques, and in particular the
global aspect of the analysis. Here we describe the second round of MLDCs
and provide details about its implementation.
Comments: Proceedings of GWDAW-11.
-----------------------------------------------------------------------------
arXiv:0704.1808
Tests of Bayesian Model Selection Techniques for Gravitational Wave
Astronomy
Authors: Neil J. Cornish, Tyson B. Littenberg
(Submitted on 13 Apr 2007 (v1), last revised 8 Nov 2007 (this version, v3))
11 pages
The analysis of gravitational wave data involves many model selection
problems. The most important example is the detection problem of selecting
between the data being consistent with instrument noise alone, or
instrument noise and a gravitational wave signal. The analysis of data
from ground based gravitational wave detectors is mostly conducted using
classical statistics, and methods such as the Neyman-Pearson criteria are
used for model selection. Future space based detectors, such as the
\emph{Laser Interferometer Space Antenna} (LISA), are expected to produced
rich data streams containing the signals from many millions of sources.
Determining the number of sources that are resolvable, and the most
appropriate description of each source poses a challenging model selection
problem that may best be addressed in a Bayesian framework. An important
class of LISA sources are the millions of low-mass binary systems within our
own galaxy, tens of thousands of which will be detectable. Not only are
the number of sources unknown, but so are the number of parameters required
to model the waveforms. For example, a significant subset of the resolvable
galactic binaries will exhibit orbital frequency evolution, while a smaller
number will have measurable eccentricity. In the Bayesian approach to model
selection one needs to compute the Bayes factor between competing models.
Here we explore various methods for computing Bayes factors in the context
of determining which galactic binaries have measurable frequency evolution.
The methods explored include a Reverse Jump Markov Chain Monte Carlo (RJMCMC)
algorithm, Savage-Dickie density ratios, the Schwarz-Bayes Information
Criterion (BIC), and the Laplace approximation to the model evidence. We
find good agreement between all of the approaches.
-----------------------------------------------------------------------------
arXiv:0704.2917
Extracting galactic binary signals from the first round of Mock LISA Data
Challenges
Authors: Jeff Crowder, Neil J. Cornish
(Submitted on 23 Apr 2007)
We report on the performance of an end-to-end Bayesian analysis pipeline
for detecting and characterizing galactic binary signals in simulated LISA
data. Our principal analysis tool is the Blocked-Annealed Metropolis
Hasting (BAM) algorithm, which has been optimized to search for tens of
thousands of overlapping signals across the LISA band. The BAM algorithm
employs Bayesian model selection to determine the number of resolvable
sources, and provides posterior distribution functions for all the model
parameters. The BAM algorithm performed almost flawlessly on all the
Round 1 Mock LISA Data Challenge data sets, including those with many
highly overlapping sources. The only misses were later traced to a coding
error that affected high frequency sources. In addition to the BAM
algorithm we also successfully tested a Genetic Algorithm (GA), but only
on data sets with isolated signals as the GA has yet to be optimized to
handle large numbers of overlapping signals.
Comments: 13 pages, 4 figures, submitted to Proceedings of GWDAW-11
(Berlin, Dec. '06)
-----------------------------------------------------------------------------
arXiv:0711.2667
Report on the second Mock LISA Data Challenge
Authors: Stanislav Babak, John G. Baker, Matthew J. Benacquista,
Neil J. Cornish, Jeff Crowder, Curt Cutler, Shane L. Larson,
Tyson B. Littenberg, Edward K. Porter, Michele Vallisneri,
Alberto Vecchio (the Mock LISA Data Challenge task force), Gerard Auger,
Leor Barack, Arkadiusz Blaut, Ed Bloomer, Duncan A. Brown,
Nelson Christensen, James Clark, Stephen Fairhurst, Jonathan R. Gair,
Hubert Halloin, Martin Hendry, Arturo Jimenez, Andrzej Krolak, Ilya Mandel,
Chris Messenger, Renate Meyer, Soumya Mohanty, Rajesh Nayak,
Antoine Petiteau, Matt Pitkin, Eric Plagnol, Reinhard Prix,
Emma L. Robinson, Christian Roever, Pavlin Savov, Alexander Stroeer,
Jennifer Toher, John Veitch, Jean-Yves Vinet, Linqing Wen, John T. Whelan,
Graham Woan (the Challenge 2 participants)
(Submitted on 16 Nov 2007)
The Mock LISA Data Challenges are a program to demonstrate LISA
data-analysis capabilities and to encourage their development. Each round
of challenges consists of several data sets containing simulated instrument
noise and gravitational-wave sources of undisclosed parameters. Participants
are asked to analyze the data sets and report the maximum information about
source parameters. The challenges are being released in rounds of increasing
complexity and realism: in this proceeding we present the results of
Challenge 2, issued in January 2007, which successfully demonstrated the
recovery of signals from supermassive black-hole binaries, from ~20,000
overlapping Galactic white-dwarf binaries, and from the extreme-mass-ratio
inspirals of compact objects into central galactic black holes.
Comments: 8 pages, 2 EPS figures, proceedings of the 7th Amaldi Conference
on Gravitational Waves, 8-14 July 2007, Sydney, Australia.
-----------------------------------------------------------------------------
arXiv:0707.0339
The BSSN formulation is a partially constrained evolution system
Authors: Adrian P. Gentle
(Submitted on 3 Jul 2007 (v1), last revised 17 Jul 2007 (this version, v2))
8 pages
Relativistic simulations in 3+1 dimensions typically monitor the Hamiltonian
and momentum constraints during evolution, with significant violations of
these constraints indicating the presence of instabilities. In this paper we
rewrie the momentum constraints as first-order evolution equations, and show
that the popular BSSN formulation of the Einstein equations explicitly uses
the momentum constraints as evolution equations. We conjecture that this
feature is a key reason for the relative success of the BSSN formulation in
numerical relativity.
-----------------------------------------------------------------------------
arXiv:gr-qc/0612007
Spherically Symmetric Gravitational Collapse of General Fluids
Authors: Paul Lasky, Anthony Lun
(Submitted on 1 Dec 2006)
11 pages
We express Einstein's field equations for a spherically symmetric ball of
eneral fluid such that they are conducive to an initial value problem. We
show how the equations reduce to the Vaidya spacetime in a non-null
coordinate frame, simply by designating specific equations of state.
Furthermore, this reduces to the Schwarzschild spacetime when all matter
variables vanish. We then describe the formulation of an initial value
problem, whereby a general fluid ball with vacuum exterior is established
on an initial spacelike slice. As the system evolves, the fluid ball
collapses and emanates null radiation such that a region of Vaidya
spacetime develops. Therefore, on any subsequent spacelike slice there
exists three regions; general fluid, Vaidya and Schwarzschild, all
expressed in a single coordinate patch with two free-boundaries determined
by the equations. This implies complicated matching schemes are not
required at the interfaces between the regions, instead, one simply
requires the matter variables tend to the appropriate equations of state.
We also show the reduction of the system of equations to the static cases,
and show staticity necessarily implies zero ``heat flux''. Furthermore,
the static equations include a generalization of the Tolman-Oppenheimer-
Volkoff equations for hydrostatic equilibrium to include anisotropic
stresses in general coordinates.
Journal reference: Phys.Rev. D75 (2007) 024031
-----------------------------------------------------------------------------
arXiv:0704.3634
Gravitational collapse of spherically symmetric plasmas in Einstein-Maxwell
spacetimes
Authors: Paul Lasky, Anthony Lun
(Submitted on 26 Apr 2007 (v1), last revised 7 May 2007 (this version, v2))
We utilize a recent formulation of a spherically symmetric spacetime
endowed with a general decomposition of the energy momentum tensor [Phys.
Rev. D, 75, 024031 (2007)] to derive equations governing spherically
symmetric distributions of electromagnetic matter. We show the system
reduces to the Reissner-Nordstrom spacetime in general, spherically
symmetric coordinates in the vacuum limit. Furthermore, we show reduction
to the charged Vaidya spacetime in non-null coordinates when certain
equations of states are chosen. A model of gravitational collapse is
discussed whereby a charged fluid resides within a boundary of finite
radial extent on the initial hypersurface, and is allowed to radiate
charged particles. Our formalism allows for the discussion of all regions
in this model without the need for complicated matching schemes at the
interfaces between successive regions. As further examples we consider
the collapse of a thin shell of charged matter onto a Reissner-Nordstrom
black hole. Finally, we reduce the entire system of equations to the
static case such that we have the equations for hydrostatic equilibrium of
a charged fluid.
Journal reference: Phys. Rev. D, 75, 104010 (2007)
-----------------------------------------------------------------------------
arXiv:hep-th/0702002
Gauss-Bonnet cosmologies: crossing the phantom divide and the transition
from matter dominance to dark energy
Authors: Ben M. Leith, Ishwaree P. Neupane
(Submitted on 1 Feb 2007 (v1), last revised 23 May 2007 (this version, v2))
44 pages
Dark energy cosmologies with an equation of state parameter $w$ less than -1
are often found to violate the null energy condition and show unstable
behaviour. A solution to this problem may require the existence of a
consistent effective theory that violates the null energy condition only
momentarily and does not develop any instabilities or other pathological
features for a late time cosmology. A model which incorporates a dynamical
scalar field $\phi$ coupled to the quadratic Riemann invariant of the
Gauss-Bonnet form is a viable proposal. Such an effective theory is shown to
admit nonsingular cosmological evolutions for a wide range of
scalar-Gauss-Bonnet coupling. We discuss the conditions for which our model
yields observationally supported spectra of scalar and tensor fluctuations,
under cosmological perturbations. The model can provide a reasonable
explanation for the transition from matter dominance to dark energy regime
and the late time cosmic acceleration, offering an interesting testing
ground for investigations of the cosmological modified gravity.
Journal reference: JCAP 0705 (2007) 019
-----------------------------------------------------------------------------
arXiv:0709.2535
Gravitational energy as dark energy: Concordance of cosmological tests
Authors: Ben M. Leith, S. C. Cindy Ng, David L. Wiltshire
(Submitted on 17 Sep 2007 (v1), last revised 21 Nov 2007 (this version, v2))
We provide preliminary quantitative evidence that a new solution to
averaging the observed inhomogeneous structure of matter in the universe
[gr-qc/0702082, arxiv:0709.0732], may lead to an observationally viable
cosmology without exotic dark energy. We find parameters which
simultaneously satisfy three independent tests: the match to the angular
scale of the sound horizon detected in the cosmic microwave background
anisotropy spectrum; the effective comoving baryon acoustic oscillation
scale detected in galaxy clustering statistics; and type Ia supernova
luminosity distances. Independently of the supernova data, concordance is
obtained for a value of the Hubble constant which agrees with the
measurement of the Hubble Key team of Sandage et al [astro-ph/0603647].
Best-fit parameters include a global average Hubble constant H_0 = 61.7
(+1.2/-1.1) km/s/Mpc, a present epoch void volume fraction of f_{v0} = 0.76
(+0.12/-0.09), and an age of the universe of 14.7 (+0.7/-0.5) billion years
as measured by observers in galaxies. The mass ratio of non-baryonic dark
matter to baryonic matter is 3.1 (+2.5/-2.4), computed with a
baryon-to-photon ratio that concords with primordial lithium abundances.
Comments: 4 pages, 2 figures; v2 improved statistics, references added,
to appear in ApJ Letters.
-----------------------------------------------------------------------------
arXiv:0709.2541
Non-minimally coupled multi-scalar black holes
Authors: Ben M. Leith, Alex B. Nielsen
(Submitted on 17 Sep 2007)
6 pages
We study the static, spherically symmetric black hole solutions for a
non-minimally coupled multi-scalar theory. We find numerical solutions for
values of the scalar fields when a certain constraint on the maximal charge
is satisfied. Beyond this constraint no black hole solutions exist. This
constraint therefore corresponds to extremal solutions, however, this does
not match the \kappa = 0 constraint which typically indicates extremal
solutions in other models. This implies that the set of extremal solutions
have non-zero, finite and varying surface gravity. These solutions also
violate the no-hair theorems for N>1 scalar fields and have previously been
proven to be linearly stable.
-----------------------------------------------------------------------------
arXiv:0710.3140
Numerical wave optics and the lensing of gravitational waves by globular
clusters
Authors: Andrew J. Moylan, David E. McClelland, Susan M. Scott,
Antony C. Searle, G. V. Bicknell
(Submitted on 16 Oct 2007)
We consider the possible effects of gravitational lensing by globular
clusters on gravitational waves from asymmetric neutron stars in our galaxy.
In the lensing of gravitational waves, the long wavelength, compared with
the usual case of optical lensing, can lead to the geometrical optics
approximation being invalid, in which case a wave optical solution is
necessary. In general, wave optical solutions can only be obtained
numerically. We describe a computational method that is particularly well
suited to numerical wave optics. This method enables us to compare the
properties of several lens models for globular clusters without ever
calling upon the geometrical optics approximation, though that
approximation would sometimes have been valid. Finally, we estimate the
probability that lensing by a globular cluster will significantly affect
the detection, by ground-based laser interferometer detectors such as LIGO,
of gravitational waves from an asymmetric neutron star in our galaxy,
finding that the probability is insignificantly small.
Comments: To appear in: Proceedings of the Eleventh Marcel Grossmann
Meeting
-----------------------------------------------------------------------------
arXiv:0710.3108
Functional programming framework for GRworkbench
Authors: Andrew J. Moylan, Susan M. Scott, Antony C. Searle
(Submitted on 16 Oct 2007)
The software tool GRworkbench is an ongoing project in visual, numerical
General Relativity at The Australian National University. Recently, the
numerical differential geometric engine of GRworkbench has been rewritten
using functional programming techniques. By allowing functions to be
directly represented as program variables in C++ code, the functional
framework enables the mathematical formalism of Differential Geometry to be
more closely reflected in GRworkbench . The powerful technique of 'automatic
differentiation' has replaced numerical differentiation of the metric
components, resulting in more accurate derivatives and an order-of-magnitude
performance increase for operations relying on differentiation.
Journal reference: Moylan, A J, S M Scott, and A C Searle. 2005. Functional
programming framework for GRworkbench. General Relativity and Gravitation 37,
no. 9 (September): 1517-1528
-----------------------------------------------------------------------------
arXiv:0710.3435
Numerical experimentation within GRworkbench
Authors: Andrew Moylan
(Submitted on 18 Oct 2007)
The software tool GRworkbench is an ongoing project in visual, numerical
General Relativity at The Australian National University. This year,
GRworkbench has been significantly extended to facilitate numerical
experimentation. The numerical differential geometric engine has been
rewritten using functional programming techniques, enabling fundamental
concepts to be directly represented as variables in the C++ code of
GRworkbench. Sophisticated general numerical methods have replaced simpler
specialised algorithms. Various tools for numerical experimentation have
been implemented, allowing for the simulation of complex physical
situations.
A recent claim, that the mass of the Milky Way can be measured using a small
interferometer located on the surface of the Earth, has been investigated,
and found to be an artifact of the approximations employed in the analysis.
This difficulty is symptomatic of the limitations of traditional
pen-and-paper analysis in General Relativity, which was the motivation
behind the original development of GRworkbench. The physical situation
pertaining to the claim has been modelled in a numerical experiment in
GRworkbench, without the necessity of making any simplifying assumptions,
and an accurate estimate of the effect has been obtained.
Comments: Honours thesis (ANU, 2003)
-----------------------------------------------------------------------------
arXiv:0704.1669
Possible polarisation and spin dependent aspects of quantum gravity
Authors: D. V. Ahluwalia-Khalilova, N. G. Gresnigt, Alex B. Nielsen,
D. Schritt, T. F. Watson (University of Canterbury, New Zealand)
(Submitted on 12 Apr 2007 (v1), last revised 8 Jun 2007 (this version, v2))
We argue that quantum gravity theories that carry a Lie algebraic
modification of the Poincare' and Heisenberg algebras inevitably provide
inhomogeneities that may serve as seeds for cosmological structure formation.
Furthermore, in this class of theories one must expect a strong polarisation
and spin dependence of various quantum-gravity effects.
Comments: Awarded an "honourable mention" in the 2007 Gravity Research
Foundation Essay Competition
-----------------------------------------------------------------------------
arXiv:0711.0313
Black holes as local horizons
Authors: Alex B. Nielsen
(Submitted on 2 Nov 2007)
This talk gives a brief introduction to black hole horizons and their role
in black hole thermodynamics. In particular a distinction is made between
quasi-locally defined horizons and event horizons. Currently some new
techniques have led to interesting developments and the field seems to be
growing in two distinct directions. We will show how thermodynamics can
equally well be applied to locally defined horizons and discuss some recent
results. The emphasis is on giving simple intuitive pictures and
mathematical details are largely omitted.
Comments: Talk presented at KPS meeting, 18th October, 2007, Jeju, Korea,
18 pages, 5 figures
-----------------------------------------------------------------------------
arXiv:0711.1445
Dynamical surface gravity
Authors: Alex B. Nielsen, Jong Hyuk Yoon
(Submitted on 9 Nov 2007)
17 pages
We discuss how the surface gravity can be classically defined for dynamical
black holes. In particular we focus on defining the surface gravity for
locally defined horizons and compare a number definitions proposed in the
literature. We illustrate the differences between the various proposals in
the case of an arbitrary dynamical, spherically symmetric black hole
spacetime. We also discuss how the trapping horizon formalism of Hayward
can be related to other constructions.
-----------------------------------------------------------------------------
arXiv:gr-qc/0612193
The affine theory of gravitation and electromagnetism I
Authors: Nikodem J. Poplawski
(Submitted on 29 Dec 2006 (v1), last revised 31 Jan 2007 (this version, v2))
9 pages
Abstract: The affine variational principle of Eddington generates the
Einstein field equations of general relativity in vacuum with a non-zero
cosmological constant. We generalize this principle to include
electromagnetism, obtaining the Einstein-Maxwell field equations and the
Lorentz equation of motion. We vary the action with respect to the
quantities that appear in the definition of the electromagnetic covariant
derivative: the affine (nonsymmetric) connection and the electromagnetic
potential, while the Lagrangian density is taken to be the square root of
the determinant of a linear combination of the symmetrized Ricci tensor
and the electromagnetic field tensor. This construction generates a
symmetric metric tensor and a connection with torsion that depends only
on the torsion vector. The whole formulation is valid only for very weak
electromagnetic fields, on the order of the magnetic field in interstellar
space.
-----------------------------------------------------------------------------
arXiv:gr-qc/0701176
The affine theory of gravitation and electromagnetism II
Authors: Nikodem J. Poplawski
(Submitted on 31 Jan 2007 (v1), last revised 27 Feb 2007 (this version, v2))
7 pages
The Eddington Lagrangian of the purely affine theory of gravitation
generates the Einstein equations of general relativity with the
cosmological constant. The purely affine Lagrangian for the electromagnetic
field, that has the form of the Maxwell Lagrangian with the metric tensor
replaced by the symmetrized Ricci tensor, is dynamically equivalent to
the Einstein-Maxwell Lagrangian in the metric formulation. We show that
the sum of the two affine Lagrangians is not equivalent to the sum of the
analogous Lagrangians in the metric formulation. Therefore, the simplest
affine theory combining gravitation, electromagnetism and the cosmological
constant may explain unsolved physical phenomena in systems where all three
factors are important, for example, in outer regions of the Solar System or
galaxies.
-----------------------------------------------------------------------------
arXiv:gr-qc/0702129
The Maxwell Lagrangian in purely affine gravity
Authors: Nikodem J. Poplawski
(Submitted on 25 Feb 2007 (v1), last revised 27 Aug 2007 (this version, v2))
9 pages
The purely affine Lagrangian for linear electrodynamics, that has the form
of the Maxwell Lagrangian in which the metric tensor is replaced by the
symmetrized Ricci tensor, is dynamically equivalent to the Einstein-Maxwell
equations in the metric-affine and metric formulation. We show that this
equivalence is related to the invariance of the Maxwell Lagrangian under
conformal transformations of the metric tensor. We also apply to a purely
affine Lagrangian the Legendre transformation with respect to the second
Ricci tensor to show that the corresponding Legendre term and the new
Hamiltonian density are related to the Maxwell-Palatini Lagrangian for
the electromagnetic field. Therefore the purely affine picture, in addition
to generating the gravitational Lagrangian that is linear in the curvature,
justifies why the electromagnetic Lagrangian is quadratic in the
electromagnetic field.
-----------------------------------------------------------------------------
arXiv:0705.0351
A unified, purely affine theory of gravitation and electromagnetism
Authors: Nikodem J. Poplawski
(Submitted on 2 May 2007 (v1), last revised 12 Jul 2007 (this version, v4))
7 pages
In the purely affine formulation of gravity, the gravitational field is
represented by the symmetric part of the Ricci tensor of the affine
connection. The classical electromagnetic field can be represented in
this formulation by the second Ricci tensor of the connection. Such a
construction is dynamically equivalent to the sourceless Einstein-Maxwell
equations. We generalize this construction to the case with sources,
represented by the derivative of the affine Lagrangian density with
respect to the connection. We show that the Maxwell equations with
sources emerge for the simplest affine Lagrangian for matter, while the
Einstein and Lorentz equations arise if mass has electromagnetic origin.
We also show that the Maxwell equations replace the unphysical constraint
imposed by the projective invariance of purely affine Lagrangians that
depend explicitly on the connection.
-----------------------------------------------------------------------------
arXiv:0706.4474
F(R) gravity in purely affine formulation
Authors: Nikodem J. Poplawski
(Submitted on 29 Jun 2007 (v1), last revised 11 Jul 2007 (this version, v2))
4 pages
The purely affine, metric-affine and purely metric formulation of general
relativity are dynamically equivalent and the relation between them is
analogous to the relation between Lagrangian and Hamiltonian dynamics. We
show that one cannot construct a purely affine Lagrangian that is
dynamically equivalent to a metric-affine or metric F(R) Lagrangian which
is nonlinear in the curvature scalar. Thus the equivalence between the
purely affine picture and the two other formulations does not hold for
theories of gravity with a nonlinear dependence on the curvature. We also
show that this equivalence is restored if the metric tensor is conformally
transformed from the Jordan to the Einstein frame. Consequently, the
Einstein frame is physical with respect to the affine/metric (or
Lagrangian/Hamiltonian) equivalence and F(R) gravity is simply general
relativity with a scalar field, reformulated in the Jordan frame.
-----------------------------------------------------------------------------
arXiv:0709.3652
Massive vectors from projective invariance breaking
Authors: Nikodem J. Poplawski
(Submitted on 23 Sep 2007)
11 pages
A general affine connection has enough degrees of freedom to make it
possible to describe the classical gravitational and electromagnetic fields
in the metric-affine formulation of gravity. The gravitational field is
represented in the Lagrangian by the symmetric part of the Ricci tensor of
the connection and the classical electromagnetic field can be represented
by the second Ricci tensor. We show that the simplest metric-affine
Lagrangian which depends on the second Ricci tensor of the nonsymmetric
connection generates the Einstein-Maxwell equations for a massless vector.
Metric-affine Lagrangians with matter fields depending on the connection
are subject to an unphysical constraint because the symmetrized Ricci
tensor is projectively invariant while matter fields are not. We show that
the appearance of the second Ricci tensor, which is not projectively
invariant, in the Lagrangian replaces this constraint with the Maxwell
equations and restores the projective invariance of the total action. We
also show that constraints on the connection that break projective
invariance replace the massless vector with a massive vector and impose
projective invariance on the second Ricci tensor. We examine several
algebraic constraints on the torsion tensor. The conclusion is that the
metric-affine formulation of gravity allows for a mechanism that generates
mass of vectors, as it happens for electroweak gauge bosons via spontaneous
symmetry breaking.
-----------------------------------------------------------------------------
arXiv:0710.3982
Covariant differentiation of spinors for a general affine connection
Authors: Nikodem J. Poplawski
(Submitted on 22 Oct 2007 (v1), last revised 13 Nov 2007 (this version, v2))
8 pages
We show that the covariant derivative of a spinor for a general affine
connection, not restricted to be metric compatible, is given by the
Fock-Ivanenko coefficients with the antisymmetric part of the Lorentz
connection. The projective invariance of the spinor connection allows to
introduce gauge fields interacting with spinors. We also derive the
relation between the curvature spinor and the curvature tensor for a
general connection.
-----------------------------------------------------------------------------
arXiv:0711.2341
Conservation laws for a general Lorentz connection
Authors: Nikodem J. Poplawski
(Submitted on 15 Nov 2007)
7 pages
We derive conservation laws for energy-momentum (canonical and dynamical)
and angular momentum for a general Lorentz connection.
-----------------------------------------------------------------------------
arXiv:gr-qc/0703117
Trans-Planckian physics and signature change events in Bose gas
hydrodynamics
Authors: Silke Weinfurtner (Victoria University of Wellington),
Angela White (The Australian National University), Matt Visser (Victoria
University of Wellington)
(Submitted on 23 Mar 2007)
18 pages
We present an example of emergent spacetime as the hydrodynamic limit of a
more fundamental microscopic theory. The low-energy, long-wavelength limit
in our model is dominated by collective variables that generate an
effective Lorentzian metric. This system naturally exhibits a microscopic
mechanism allowing us to perform controlled signature change between
Lorentzian and Riemannian geometries. We calculate the number of particles
produced from a finite-duration Euclidean-signature event, where we take
the position that to a good approximation the dynamics is dominated by the
evolution of the linearized perturbations, as suggested by Calzetta and Hu
[Phys. Rev. A 68 (2003) 043625]. We adapt the ideas presented by Dray et al.
[Gen. Rel. Grav. 23 (1991) 967], such that the field and its canonical
momentum are continuous at the signature-change event. We investigate the
interplay between the underlying microscopic structure and the emergent
gravitational field, focussing on its impact on particle production in the
ultraviolet regime. In general, this can be thought of as the combination
of trans-Planckian physics and signature-change physics. Further we
investigate the possibility of using the proposed signature change event as
an amplifier for analogue "cosmological particle production" in condensed
matter experiments.
-----------------------------------------------------------------------------
arXiv:gr-qc/0703122
Cosmography: Extracting the Hubble series from the supernova data
Authors: Celine Cattoen (Victoria University of Wellington), Matt Visser
(Victoria University of Wellington)
(Submitted on 26 Mar 2007 (v1), last revised 31 Jul 2007 (this version, v3))
50 pages
We perform a number of inter-related cosmographic fits to the legacy05 and
gold06 supernova datasets. We pay particular attention to the influence of
both statistical and systematic uncertainties, and also to the extent to
which the choice of distance scale and manner of representing the redshift
scale affect the cosmological parameters. While the "preponderance of
evidence" certainly suggests an accelerating universe, we would argue that
(based on the supernova data) 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 graph slopes up or down.
Turning to the details of the cosmographic fits, three issues in particular
concern us: First, the fitted value for the deceleration parameter changes
significantly depending on whether one performs a chi^2 fit to the
luminosity distance, proper motion distance, angular diameter distance, or
other suitable distance surrogate. Second, the fitted value for the
deceleration parameterchanges significantly depending on whether one uses
the traditional redshift variable z, or what we shall argue is on
theoretical grounds an improved parameterization y=z/(1+z). Third, the
published estimates for systematic uncertainties are sufficiently large
that they certainly impact on, and to a large extent undermine, the usual
purely statistical tests of significance. We conclude that the case for an
accelerating universe is considerably less watertight than commonly
believed.
-----------------------------------------------------------------------------
arXiv:0705.2077
Analogue model of a FRW universe in Bose-Einstein condensates: Application
of the classical field method
Authors: Piyush Jain, Silke Weinfurtner, Matt Visser, C. W. Gardiner
(Submitted on 15 May 2007)
26 pages
Analogue models of gravity have been motivated by the possibility of
investigating phenomena not readily accessible in their cosmological
counterparts. In this paper, we investigate the analogue of cosmological
particle creation in a Friedmann-Robertson-Walker universe by numerically
simulating a Bose-Einstein condensate with a time-dependent scattering
length. In particular, we focus on a two-dimensional homogeneous condensate
using the classical field method via the truncated Wigner approximation.
We show that for various forms of the scaling function the particle
production is consistent with the underlying theory in the long wavelength
limit. In this context, we further discuss the implications of modified
dispersion relations that arise from the microscopic theory of a weakly
interacting Bose gas.
Journal reference: Phys. Rev. A 76, 033616 (2007)
-----------------------------------------------------------------------------
arXiv:0706.0622
The Kerr spacetime: A brief introduction
Authors: Matt Visser (Victoria University of Wellington)
(Submitted on 5 Jun 2007 (v1), last revised 30 Jun 2007 (this version, v2))
This chapter provides a brief introduction to the Kerr spacetime and
rotating black holes, touching on the most common coordinate
representations of the spacetime metric and the key features of the
geometry -- the presence of horizons and ergospheres. The coverage is by
no means complete, and serves chiefly to orient oneself when reading
subsequent chapters.
Comments: V2: 41 pages, 3 figures: Introductory chapter on the Kerr
spacetime that is intended for use in the book "The Kerr spacetime",
currently being edited by Susan Scott, Matt Visser, and David Wiltshire.
It is not, nor is it intended to be, complete and exhaustive.
-----------------------------------------------------------------------------
arXiv:0707.0146
Buchdahl-like transformations for perfect fluid spheres
Authors: Petarpa Boonserm (Victoria University of Wellington), Matt Visser
(Victoria University of Wellington)
(Submitted on 2 Jul 2007)
23 pages
In two previous articles [Phys. Rev. D71 (2005) 124307 (gr-qc/0503007), and
gr-qc/0607001] we have discussed several "algorithmic" techniques that
permit one (in a purely mechanical way) to generate large classes of general
relativistic static perfect fluid spheres. Working in Schwarzschild
curvature coordinates, we used these algorithmic ideas to prove several
"solution-generating theorems" of varying levels of complexity. In the
present article we consider the situation in other coordinate systems: In
particular, in general diagonal coordinates we shall generalize our
previous theorems, in isotropic coordinates we shall encounter a variant of
the so-called "Buchdahl transformation", while in other coordinate systems
(such as Gaussian polar coordinates, Synge isothermal coordinates, and
Buchdahl coordinates) we shall find a number of more complex "Buchdahl-like
transformations" and "solution-generating theorems" that may be used to
investigate and classify the general relativistic static perfect fluid
sphere. Finally by returning to general diagonal coordinates and making a
suitable ansatz for the functional form of the metric components we place
the Buchdahl transformation in its most general possible setting.
-----------------------------------------------------------------------------
arXiv:0710.1887
The Hubble series: Convergence properties and redshift variables
Authors: Celine Cattoen (Victoria University of Wellington), Matt Visser
(Victoria University of Wellington)
(Submitted on 10 Oct 2007)
15 pages
In cosmography, cosmokinetics, and cosmology it is quite common to encounter
physical quantities expanded as a Taylor series in the cosmological redshift
z. Perhaps the most well-known exemplar of this phenomenon is the Hubble
relation between distance and redshift. However, we now have considerable
high-z data available, for instance we have supernova data at least back to
redshift z=1.75. This opens up the theoretical question as to whether or not
the Hubble series (or more generally any series expansion based on the
z-redshift) actually converges for large redshift? Based on a combination of
mathematical and physical reasoning, we argue that the radius of convergence
of any series expansion in z is less than or equal to 1, and that z-based
expansions must break down for z>1, corresponding to a universe less than
half its current size. Furthermore, we shall argue on theoretical grounds for
the utility of an improved parameterization y=z/(1+z). In terms of the
y-redshift we again argue that the radius of convergence of any series
expansion in y is less than or equal to 1, so that y-based expansions are
likely to be good all the way back to the big bang y=1, but that y-based
expansions must break down for y<-1, now corresponding to a universe more
than twice its current size.
Journal reference: Class. Quantum Grav. 24 (2007) 5985-5997
-----------------------------------------------------------------------------
arXiv:0704.0628
Black hole puncture initial data with realistic gravitational wave content
Authors: Bernard J Kelly, Wolfgang Tichy, Manuela Campanelli,
Bernard F Whiting
(Submitted on 4 Apr 2007 (v1), last revised 2 Aug 2007 (this version, v2))
13 pages
We present improved post-Newtonian-inspired initial data for non-spinning
black-hole binaries, suitable for numerical evolution with punctures. We
revisit the work of Tichy et al. [W. Tichy, B. Bruegmann, M. Campanelli,
and P. Diener, Phys. Rev. D 67, 064008 (2003)], explicitly calculating the
remaining integral terms. These terms improve accuracy in the far zone
and, for the first time, include realistic gravitational waves in the
initial data. We investigate the behavior of these data both at the center
of mass and in the far zone, demonstrating agreement of the transverse-
traceless parts of the new metric with quadrupole-approximation waveforms.
These data can be used for numerical evolutions, enabling a direct
connection between the merger waveforms and the post-Newtonian inspiral
waveforms.
-----------------------------------------------------------------------------
arXiv:0706.0199
Approximate Killing Vectors on S^2
Authors: Gregory B. Cook, Bernard F. Whiting
(Submitted on 1 Jun 2007)
We present a new method for computing the best approximation to a Killing
vector on closed 2-surfaces that are topologically S^2. When solutions of
Killing's equation do not exist, this method is shown to yield results
superior to those produced by existing methods. In addition, this method
appears to provide a new tool for studying the horizon geometry of distorted
black holes.
Comments: 4 pages, 3 figures, submitted to Physical Review D
-----------------------------------------------------------------------------
arXiv:0706.4324
Conformal coordinates of a constant density star
Authors: Karthik Shankar, Bernard. F. Whiting
(Submitted on 28 Jun 2007)
13 pages
It is well known that the interior of a constant density spherical star is
conformally flat. In this paper we obtain the coordinate system in which
the conformal flatness of the metric manifests itself. In a similar way,
we also construct such coordinates for Robertson Walker metric.
-----------------------------------------------------------------------------
arXiv:0707.0042
Self force of a static electric charge near a Schwarzschild Star
Authors: Karthik Shankar, Bernard F. Whiting
(Submitted on 30 Jun 2007 (v1), last revised 6 Nov 2007 (this version, v2))
11 pages
When a charge is held static near a constant density spherical star, it
experiences a self-force which is significantly different from the force
it would experience when placed near a black hole of the same mass. In
this paper, an expression for the self-force (as measured by a locally
inertial observer) is given explicitly calculated for an insulating
Schwarzschild star, and the result is explicitly computed for the extreme
density case, which has a singularity at its center. The force is found to
be repulsive. A similar calculation of the self-force is also performed for
a conducting star. This calculation is valid for any static, spherically
conducting star, since the result is independent of the interior metric.
When the charge is placed very close to the conducting star, the force is
found to be attractive but when the charge is placed beyond a certain
distance (2.95M for a conducting star of radius 2.25M), the force is found
to be repulsive. When the charge is placed very far from the star (be it
conducting or insulating), the charge experiences the same repulsive force
it would experience when placed in the spacetime of a black hole with the
same mass as the star.
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arXiv:0710.5658
Analytic approximations, perturbation methods, and their applications
Authors: P. Jaranowski, K. G. Arun, L. Barack, L. Blanchet, A. Buonanno,
M. F. De Laurentis, S. Detweiler, H. Dittus, M. Favata, G. Faye,
J. L. Friedman, K. Ganz, W. Hikida, B. R. Iyer, T. S. Keidl, Dong-Hoon Kim,
K. D. Kokkotas, B. Kol, A. S. Kubeka, C. Lämmerzahl, J. Majár, A. Nagar,
H. Nakano, L. R. Price, M. S. S. Qusailah, N. Radicella, N. Sago, D. Singh,
H. Sotani, T. Tanaka, A. Tartaglia, M. Vasúth, I. Vega, B. F. Whiting,
A. G. Wiseman, S. Yoshida
(Submitted on 30 Oct 2007 (v1), last revised 2 Nov 2007 (this version, v2))
The paper summarizes the parallel session B3 {\em Analytic approximations,
perturbation methods, and their applications} of the GR18 conference. The
talks in the session reported notably recent advances in black hole
perturbations and post-Newtonian approximations as applied to sources of
gravitational waves.
Comments: Summary of the B3 parallel session of the GR18 conference
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arXiv:gr-qc/0702082
Cosmic clocks, cosmic variance and cosmic averages
Authors: David L. Wiltshire
(Submitted on 15 Feb 2007 (v1), last revised 1 Nov 2007 (this version, v4))
72 pages
Cosmic acceleration is explained quantitatively, purely in general
relativity, as an apparent effect due to quasilocal gravitational energy
differences that arise in the decoupling of bound systems from the global
expansion of the universe. "Dark energy" is recognised as a
misidentification of those aspects of gravitational energy which by virtue
of the equivalence principle cannot be localised, namely gradients in the
energy associated with the expansion of space and spatial curvature
variations in an inhomogeneous universe, as we observe. Gravitational
energy differences between observers in bound systems, such as galaxies,
and volume-averaged comoving locations within voids in freely expanding
space can be so large that the time dilation between the two significantly
affects the parameters of any effective homogeneous isotropic model one
fits to the universe. A new approach to cosmological averaging is
presented, which implicitly solves the Sandage-de Vaucouleurs paradox.
When combined with a nonlinear scheme for cosmological evolution with
back-reaction via the Buchert equations, a new observationally viable
quantitative model of the universe is obtained. The expansion age is
increased, allowing more time for structure formation. The baryon density
fraction obtained from primordial nucleosynthesis bounds can be
significantly larger, yet consistent with primordial lithium abundance
measurements. The angular scale of the first Doppler peak in the CMB
anisotropy spectrum fits the new model despite an average negative spatial
curvature at late epochs, resolving the anomaly associated with ellipticity
in the CMB anisotropies. A number of other testable consequences are
discussed, with the potential to profoundly change the whole of theoretical
and observational cosmology. [Abridged]
Journal reference: New J. Phys. 9 (2007) 377
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arXiv:0709.0732
Exact solution to the averaging problem in cosmology
Authors: David L. Wiltshire
(Submitted on 6 Sep 2007 (v1), last revised 1 Nov 2007 (this version, v2))
Abstract: The exact solution of a two-scale Buchert average of the Einstein
equations is derived for an inhomogeneous universe which represents a close
approximation to the observed universe. The two scales represent voids, and
the bubble walls surrounding them within which clusters of galaxies are
located. As described elsewhere [gr-qc/0702082], apparent cosmic
acceleration can be recognised as a consequence of quasilocal gravitational
energy gradients between observers in bound systems and the volume average
position in freely expanding space. With this interpretation, the new
solution presented here replaces the Friedmann solutions, in representing
the average evolution of a matter-dominated universe without exotic dark
energy, while being observationally viable.
Comments: 4 pages; v2 references added, to appear in Phys. Rev. Letters
******************************************************************************
ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc,
December 2006 - November 2007
The LIGO Scientific Collaboration is a consortium of scientific institutions
doing work on the Laser Interferometer Gravitational-Wave Observatory
(LIGO), which consists of two laser interferometers 3030 km apart, one at
Hanford, Washington State and the other at Livingston, Louisiana. The LIGO
Scientific Collaboration includes ASGRG members David McClelland, Susan Scott
and Antony Searle, who are all at the Australian National University.
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arXiv:gr-qc/0702039
Upper limits on gravitational wave emission from 78 radio pulsars
Authors: The LIGO Scientific Collaboration: B. Abbott, et al, M. Kramer,
A. G. Lyne
(Submitted on 7 Feb 2007 (v1), last revised 12 Oct 2007 (this version, v5))
We present upper limits on the gravitational wave emission from 78 radio
pulsars based on data from the third and fourth science runs of the LIGO
and GEO600 gravitational wave detectors. The data from both runs have been
combined coherently to maximise sensitivity. For the first time pulsars
within binary (or multiple) systems have been included in the search by
taking into account the signal modulation due to their orbits. Our upper
limits are therefore the first measured for 56 of these pulsars. For the
remaining 22, our results improve on previous upper limits by up to a
factor of 10. For example, our tightest upper limit on the gravitational
strain is 2.6e-25 for PSRJ1603-7202, and the equatorial ellipticity of
PSRJ2124-3358 is less than 10^{-6}. Furthermore, our strain upper limit
for the Crab pulsar is only 2.2 times greater than the fiducial spin-
down limit.
Comments: 21 pages, published in Phys. Rev. D
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arXiv:gr-qc/0703068
First Cross-Correlation Analysis of Interferometric and Resonant-Bar
Gravitational-Wave Data for Stochastic Backgrounds
Authors: LIGO Scientific Collaboration, ALLEGRO Collaboration:
B. Abbott, et al
(Submitted on 12 Mar 2007)
17 pages
Data from the LIGO Livingston interferometer and the ALLEGRO resonant bar
detector, taken during LIGO's fourth science run, were examined for cross-
correlations indicative of a stochastic gravitational-wave background in
the frequency range 850-950 Hz, with most of the sensitivity arising
between 905 Hz and 925 Hz. ALLEGRO was operated in three different
orientations during the experiment to modulate the relative sign of
gravitational-wave and environmental correlations. No statistically
significant correlations were seen in any of the orientations, and the
results were used to set a Bayesian 90% confidence level upper limit of
Omega_gw(f) <= 1.02, which corresponds to a gravitational wave strain at
915 Hz of 1.5e-23/rHz. In the traditional units of h_100^2 Omega_gw(f),
this is a limit of 0.53, two orders of magnitude better than the previous
direct limit at these frequencies. The method was also validated with
successful extraction of simulated signals injected in hardware and
software.
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arXiv:astro-ph/0703234
Upper limit map of a background of gravitational waves
Authors: The LIGO Scientific Collaboration: B. Abbott, et al
(Submitted on 9 Mar 2007)
11 pages
We searched for an anisotropic background of gravitational waves using data
from the LIGO S4 science run and a method that is optimized for point
sources. This is appropriate if, for example, the gravitational wave
background is dominated by a small number of distinct astrophysical sources.
No signal was seen. Upper limit maps were produced assuming two different
power laws for the source strain power spectrum. For an f^-3 power law and
using the 50 Hz to 1.8 kHz band the upper limits on the source strain power
spectrum vary between 1.2e-48 Hz^-1 (100 Hz/f)^3 and 1.2e-47 Hz^-1
(100 Hz /f)^3, depending on the position in the sky. Similarly, in the case
of constant strain power spectrum, the upper limits vary between 8.5e-49
Hz^-1 and 6.1e-48 Hz^-1.
As a side product a limit on an isotropic background of gravitational waves
was also obtained. All limits are at the 90% confidence level. Finally, as
an application, we focused on the direction of Sco-X1, the closest low-mass
X-ray binary. We compare the upper limit on strain amplitude obtained by
this method to expectations based on the X-ray luminosity of Sco-X1.
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arXiv:0704.0943
Search for gravitational-wave bursts in LIGO data from the fourth science run
Authors: LIGO Scientific Collaboration
(Submitted on 6 Apr 2007 (v1), last revised 9 Oct 2007 (this version, v3))
The fourth science run of the LIGO and GEO 600 gravitational-wave detectors,
carried out in early 2005, collected data with significantly lower noise
than previous science runs. We report on a search for short-duration
gravitational-wave bursts with arbitrary waveform in the 64-1600 Hz
frequency range appearing in all three LIGO interferometers. Signal
consistency tests, data quality cuts, and auxiliary-channel vetoes are
applied to reduce the rate of spurious triggers. No gravitational-wave
signals are detected in 15.5 days of live observation time; we set a
frequentist upper limit of 0.15 per day (at 90% confidence level) on the
rate of bursts with large enough amplitudes to be detected reliably. The
amplitude sensitivity of the search, characterized using Monte Carlo
simulations, is several times better than that of previous searches. We also
provide rough estimates of the distances at which representative supernova
and binary black hole merger signals could be detected with 50% efficiency
by this analysis.
Comments: 30 pages, submitted to Classical and Quantum Gravity
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arXiv:0704.3368
Search for gravitational waves from binary inspirals in S3 and S4 LIGO data
Authors: LIGO Scientific Collaboration: B. Abbott, et al
(Submitted on 25 Apr 2007 (v1), last revised 26 Apr 2007 (this version, v2))
12 pages
We report on a search for gravitational waves from the coalescence of
compact binaries during the third and fourth LIGO science runs. The search
focused on gravitational waves generated during the inspiral phase of the
binary evolution. In our analysis, we considered three categories of compact
binary systems, ordered by mass: (i) primordial black hole binaries with
masses in the range 0.35 M(sun) < m1, m2 < 1.0 M(sun), (ii) binary neutron
stars with masses in the range 1.0 M(sun) < m1, m2 < 3.0 M(sun), and (iii)
binary black holes with masses in the range 3.0 M(sun)< m1, m2 < m_(max)
with the additional constraint m1+m2 < m_(max), where m_(max) was set to
40.0 M(sun) and 80.0 M(sun) in the third and fourth science runs,
respectively. Although the detectors could probe to distances as far as tens
of Mpc, no gravitational-wave signals were identified in the 1364 hours of
data we analyzed. Assuming a binary population with a Gaussian distribution
around 0.75-0.75 M(sun), 1.4-1.4 M(sun), and 5.0-5.0 M(sun), we derived
90%-confidence upper limit rates of 4.9 yr^(-1) L10^(-1) for primordial
black hole binaries, 1.2 yr^(-1) L10^(-1) for binary neutron stars, and
0.5 yr^(-1) L10^(-1) for stellar mass binary black holes, where L10 is
10^(10) times the blue light luminosity of the Sun.
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arXiv:0708.3818
All-sky search for periodic gravitational waves in LIGO S4 data
Authors: LIGO Scientific Collaboration: B. Abbott, et al
(Submitted on 28 Aug 2007)
39 pages
We report on an all-sky search with the LIGO detectors for periodic
gravitational waves in the frequency range 50-1000 Hz and with the
frequency's time derivative in the range -1.0E-8 Hz/s to zero. Data from
the fourth LIGO science run (S4) have been used in this search. Three
different semi-coherent methods of transforming and summing strain power
from Short Fourier Transforms (SFTs) of the calibrated data have been
used. The first, known as "StackSlide", averages normalized power from
each SFT. A "weighted Hough" scheme is also developed and used, and which
also allows for a multi-interferometer search. The third method, known as
"PowerFlux", is a variant of the StackSlide method in which the power is
weighted before summing. In both the weighted Hough and PowerFlux methods,
the weights are chosen according to the noise and detector antenna-pattern
to maximize the signal-to-noise ratio. The respective advantages and
disadvantages of these methods are discussed. Observing no evidence of
periodic gravitational radiation, we report upper limits; we interpret
these as limits on this radiation from isolated rotating neutron stars.
The best population-based upper limit with 95% confidence on the
gravitational-wave strain amplitude, found for simulated sources
distributed isotropically across the sky and with isotropically
distributed spin-axes, is 4.28E-24 (near 140 Hz). Strict upper limits are
also obtained for small patches on the sky for best-case and worst-case
inclinations of the spin axes.
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arXiv:0709.0766
Search for Gravitational Waves Associated with 39 Gamma-Ray Bursts Using
Data from the Second, Third, and Fourth LIGO Runs
Authors: LIGO Scientific Collaboration
(Submitted on 6 Sep 2007)
Abstract: We present the results of a search for short-duration
gravitational-wave bursts associated with 39 gamma-ray bursts (GRBs)
detected by gamma-ray satellite experiments during LIGO's S2, S3, and S4
science runs. The search involves calculating the crosscorrelation between
two interferometer data streams surrounding the GRB trigger time. We search
for associated gravitational radiation from single GRBs, and also apply
statistical tests to search for a gravitational-wave signature associated
with the whole sample. For the sample examined, we find no evidence for the
association of gravitational radiation with GRBs, either on a single-GRB
basis or on a statistical basis. Simulating gravitational-wave bursts with
sine-gaussian waveforms, we set upper limits on the root-sum-square of the
gravitational-wave strain amplitude of such waveforms at the times of the
GRB triggers. We also demonstrate how a sample of several GRBs can be used
collectively to set constraints on population models. The small number of
GRBs and the significant change in sensitivity of the detectors over the
three runs, however, limits the usefulness of a population study for the
S2, S3, and S4 runs. Finally, we discuss prospects for the search
sensitivity for the ongoing S5 run, and beyond for the next generation of
detectors.
Comments: 23 pages, 10 figures, 14 tables; to be submitted to Phys. Rev. D
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arXiv:0710.0497
A Joint Search for Gravitational Wave Bursts with AURIGA and LIGO
Authors: AURIGA Collaboration, LIGO Scientific Collaboration:
L. Baggio et al
(Submitted on 2 Oct 2007)
18 pages
The first simultaneous operation of the AURIGA detector and the LIGO
observatory was an opportunity to explore real data, joint analysis methods
between two very different types of gravitational wave detectors: resonant
bars and interferometers. This paper describes a coincident gravitational
wave burst search, where data from the LIGO interferometers are cross-
correlated at the time of AURIGA candidate events to identify coherent
transients. The analysis pipeline is tuned with two thresholds, on the
signal-to-noise ratio of AURIGA candidate events and on the significance
of the cross-correlation test in LIGO. The false alarm rate is estimated by
introducing time shifts between data sets and the network detection
efficiency is measured with simulated signals with power in the narrower
AURIGA band. In the absence of a detection, we discuss how to set an upper
limit on the rate of gravitational waves and to interpret it according to
different source models. Due to the short amount of analyzed data and to
the high rate of non-Gaussian transients in the detectors noise at the
time, the relevance of this study is methodological: this was the first
joint search for gravitational wave bursts among detectors with such
different spectral sensitivity and the first opportunity for the resonant
and interferometric communities to unify languages and techniques in the
pursuit of their common goal.
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arXiv:0710.4898
Report on an all-sky LIGO search for periodic gravitational waves in the
S4 data
Authors: Alicia M. Sintes, for the LIGO Scientific Collaboration
(Submitted on 25 Oct 2007)
We report on an all-sky search with the LIGO detectors for periodic
gravitational waves in the frequency range 50-1000 Hz and having a
negative frequency time derivative with magnitude between zero and
$10^{-8}$ Hz/s. Data from the fourth LIGO science run have been used
in this search. Three different semi-coherent methods of summing strain
power were applied. Observing no evidence for periodic gravitational
radiation, we report upper limits on strain amplitude and interpret
these limits to constrain radiation from rotating neutron stars.
Comments: 5 pages, 1 figure, presented at Amaldi7, Sydney (July 2007)
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arXiv:0711.1163
Implications for the Origin of GRB 070201 from LIGO Observations
Authors: LIGO Scientific Collaboration, K. Hurley
(Submitted on 8 Nov 2007 (v1), last revised 28 Nov 2007 (this version, v2))
We analyzed the available LIGO data coincident with GRB 070201, a short
duration hard spectrum gamma-ray burst whose electromagnetically
determined sky position is coincident with the spiral arms of the Andromeda
galaxy (M31). Possible progenitors of such short hard GRBs include mergers
of neutron stars or a neutron star and black hole, or soft gamma-ray
repeater (SGR) flares. These events can be accompanied by gravitational-
wave emission. No plausible gravitational wave candidates were found
within a 180 s long window around the time of GRB 070201. This result
implies that a compact binary progenitor of GRB 070201, with masses in the
range 1 M_sun < m_1 < 3 M_sun and 1 M_sun < m_2 < 40 M_sun, located in M31
is excluded at >99% confidence. Indeed, if GRB 070201 were caused by a
binary neutron star merger, we find that D < 3.5 Mpc is excluded, assuming
random inclination, at 90% confidence. The result also implies that an
unmodeled gravitational wave burst from GRB 070201 most probably emitted
less than 4.4 x 10^(-4) M_sun c^2 (7.9 x 10^(50) ergs) in any 100 ms long
period within the signal region if the source was in M31 and radiated
isotropically at the same frequency as LIGO's peak sensitivity
(f ~ 150 Hz). This upper limit does not exclude current models of SGRs at
the M31 distance.
Comments: 10 pages 5 figures 1 table to be submitted to ApJ
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arXiv:0711.3041
LIGO: The Laser Interferometer Gravitational-Wave Observatory
Authors: The LIGO Scientific Collaboration: B. Abbott, et al
(Submitted on 19 Nov 2007)
27 pages
The goal of the Laser Interferometric Gravitational-Wave Observatory (LIGO)
is to detect and study gravitational waves of astrophysical origin. Direct
detection of gravitational waves holds the promise of testing general
relativity in the strong-field regime, of providing a new probe of exotic
objects such as black hole and neutron stars, and of uncovering
unanticipated new astrophysics. LIGO, a joint Caltech-MIT project
supported by the National Science Foundation, operates three multi-
kilometer interferometers at two widely separated sites in the United
States. These detectors are the result of decades of worldwide technology
development, design, construction, and commissioning. They are now
operating at their design sensitivity, and are sensitive to gravitational
wave strains as small as 1 part in 1E21. With this unprecedented
sensitivity, the data are being analyzed for gravitational waves from a
variety of potential astrophysical sources.
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