Subject: ASGRG Newsletter #17 ****************************************************************************** AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION Electronic Newsletter -- #17, 2007 ****************************************************************************** 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. ****************************************************************************** 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 ****************************************************************************** Report on 18th International Conference on General Relativity and Gravitation (GRG18) -------------------------------------------------------------------------- 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 ****************************************************************************** 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. ****************************************************************************** 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. ****************************************************************************** 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. ****************************************************************************** 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/ ****************************************************************************** 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. ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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 ----------------------------------------------------------------------------- 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 ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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 ----------------------------------------------------------------------------- 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 ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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 ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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 ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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 ----------------------------------------------------------------------------- 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. ----------------------------------------------------------------------------- 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) ----------------------------------------------------------------------------- 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 ----------------------------------------------------------------------------- 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. -----------------------------------------------------------------------------