Subject: ASGRG Newsletter #18 ****************************************************************************** AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION Electronic Newsletter -- #18, 2008 ****************************************************************************** Items for this newsletter should be emailed to the editor: asgrg *AT* hotmail *DOT* com The deadline for the next issue is 31 October, 2009. ****************************************************************************** CONTENTS: * REPORT ON AMSI WORKSHOP ON MATHEMATICAL GENERAL RELATIVITY * MEMBERSHIP DETAILS ONLINE at http://www.physics.adelaide.edu.au/ASGRG/members.html * SUBSCRIPTIONS * FORTHCOMING MEETINGS * MEMBERS' ABSTRACTS at gr-qc, December 2007 - November 2008 * ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc, December 2007 - November 2008 ****************************************************************************** Report on AMSI Workshop on Mathematical General Relativity -------------------------------------------------------------------------- AMSI WORKSHOP ON MATHEMATICAL RELATIVITY: UNIVERSITY OF MELBOURNE, 7-9 JULY 2007 A 3-day Workshop on mathematical general relativity was held in the Australian Mathematical Sciences Institute (AMSI) Building on the Melbourne University campus in July. The Workshop was organised by Con Lozanovski of Swinburne Institute of Technology, who single- handedly drafted an impressive line-up of invited speakers and coaxed generous sponsorship from the AMSI, the ASGRG, Swinburne and software suppliers Analytica. The keynote speakers were: * Joerg Frauendiener of the University of Otago, who spoke about the relativistic theory of elasticity in the limit of static spherical symmetry, * Susan Scott of the Australian National University, who spoke about the application of conformal structures to future cosmological singularities, * Todd Oliynyk, who spoke about second-order Newtonian expansions for perfect fluids, * Matthew Choptuik of the University of British Columbia, who spoke about numerical tests of the cosmic censorship conjecture, * Robert Bartnik of Monash University, who spoke about geometric boundary conditions for the Ricci tensor, * Edward Fackerell of the University of Sydney, who spoke on the 1-Killing-vector vacuum Einstein equations, * Peter Szekeres of the University of Adelaide, who spoke about conformal gravity and the variation of fundamental constants, and * Pengzi Miao of Monash University, who spoke about the first variation of quasi-local mass. The other contributing speakers were Chris Goddard (Melbourne), Celine Cattoen (Wellington), Gabriel Abreu (Wellington), Petarpa Boonserm (Weliington), Florian Beyer (Albert Einstein Institute), Leo Brewin (Monash), Jules Katjar (Monash), Malcolm Anderson (Brunei) and Con Lozanovski (Swinburne). Celine Cattoen won the prize for the best student presentation, and was awarded a copy of Roger Penrose's "The Road to Reality". The weather in Melbourne during the workshop was unfortunately cold and wet, but we were compensated with a superb conference dinner at the Brandon Hotel in Carlton North on July 8 (all free courtesy of the sponsors). Warm thanks to Con Lozanovski for hosting such an enjoyable metting. Malcolm Anderson ****************************************************************************** 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 2009 - June 2010 subscriptions are requested, if you wish to pay for July 2010 - June 2011 at the same time, it may simplify matters. ****************************************************************************** FORTHCOMING MEETINGS February 24-27, 2009: 3rd High-Frequency Gravitational Wave Workshop (HFGW3) Von Braun Center, Huntsville, Alabama, USA http://www.maths.qmul.ac.uk/hyperspace/conference/08May.9.html April 13-17, 2009: Grav 09 Hotel del Lago - La Falda, Cordoba, Argentina httP://www.famaf.unc.edu.ar/~gdotti/grg/grav09/grav09.htm April 27 - May 1, 2009: IAU Symposium 261 "Relativity in Fundamental Astronomy: Dynamics, Reference Frames and Fundamental Astronomy" Cavalier Hotel, Virginia Beach, Virginia, USA http://www.aas.org/divisions/meetings/iau/ May 25-30, 2009: APCTP-BLTP JINR Joint Workshop "Frontiers in Black Hole Physics at Dubna" Dubna, Russia http://fbhp.jinr.ru/ June 4-5, 2009: Ecole Internationale Daniel Chalonge "Physics of the Standard Model of the Universe: Theory and Observations" Cite Internationale Universitaire de Paris, Paris, France http://chalonge.obspm.fr/colloque_ES2009.html June 18-19, 2009: Mathematical Relativity in Lisbon Instituto Superior Tecnico, Lisbon, Portugal http://www.math.ist.utl.pt/~jnatar/Mira/ June 28 - July 2, 2009: IX Asia-Pacific Conference on Gravitation and Astrophysics (ICGA9) Huazhong university of Science and Technology, Wuhan, China http://ggg.hust.edu.cn/ICGA9/icga9.htm June 29 - July 1, 2009: The Unity of the Universe Institute of Cosmology and Gravitation, University of Portsmouth, UK http://www.icg.port.ac.uk/sciama09/ June 29 - July 3, 2009: Invisible Universe UNESCO Headquarters, Paris, France http://www.universe2009.obspm.fr/ July 12-18, 2009: 12th Marcel Grossman Meeting on General Relativity UNESCO Headquarters, Paris, France http://www.icra.it/MG/mg12/en/ September 14-19, 2009: Grassmannian Conference in Fundamental Cosmology University of Szczeczin, Szczeczin, Poland http://cosmo.fiz.univ.szczecin.pl/ October 26-30, 2009: First Galileo-Xu Guangqi Meeting "The Sun, the Stars, the Universe and General Relativity" Shanghai, China http://www.icranet.org/index.php/ ****************************************************************************** MEMBERS' ABSTRACTS at gr-qc, December 2007 - November 2008 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:0802.3332v2 Searching for gravitational waves from Cassiopeia A with LIGO Authors: K. Wette, B. J. Owen, B. Allen, M. Ashley, J. Betzwieser, N. Christensen, T. D. Creighton, V. Dergachev, I. Gholami, E. Goetz, R. Gustafson, D. Hammer, D. I. Jones, B. Krishnan, M. Landry, B. Machenschalk, D. E. McClelland, G. Mendell, C. J. Messenger, M. A. Papa, P. Patel, M. Pitkin, H. J. Pletsch, R. Prix, K. Riles, L. Sancho de la Jordana, S. M. Scott, A. M. Sintes, M. Trias, J. T. Whelan, G. Woan (Submitted on 22 Feb 2008 (v1), last revised 8 Oct 2008 (this version, v2)) 8 pages, 1 figure We describe a search underway for periodic gravitational waves from the central compact object in the supernova remnant Cassiopeia A. The object is the youngest likely neutron star in the Galaxy. Its position is well known, but the object does not pulse in any electromagnetic radiation band and thus presents a challenge in searching the parameter space of frequency and frequency derivatives. We estimate that a fully coherent search can, with a reasonable amount of time on a computing cluster, achieve a sensitivity at which it is theoretically possible (though not likely) to observe a signal even with the initial LIGO noise spectrum. Cassiopeia A is only the second object after the Crab pulsar for which this is true. The search method described here can also obtain interesting results for similar objects with current LIGO sensitivity. Journal reference: Class. Quantum Grav. 25 235011 (2008) ----------------------------------------------------------------------------- arXiv:0802.3263v1 Quadratic superconducting cosmic strings revisited Authors: Mustapha Azreg-Aďnou (Submitted on 22 Feb 2008) 6 pages It has been shown that 5-dimensional general relativity action extended by appropriate quadratic terms admits a singular superconducting cosmic string solution. We search for cosmic strings endowed with similar and extended physical properties by directly integrating the non-linear matrix field equations thus avoiding the perturbative approach by which we constructed the above-mentioned \textsl{exact} solution. The most general superconducting cosmic string, subject to some constraints, will be derived and shown to be mathematically \textsl{unique} up to linear coordinate transformations mixing its Killing vectors. The most general solution, however, is not globally equivalent to the old one due to the existence of Killing vectors with closed orbits. Journal reference: Europhys.Lett.81:60003,2008 ----------------------------------------------------------------------------- arXiv:0801.1150v1 Observation of Three Mode Parametric Interactions in Long Optical Cavities Authors: C. Zhao, L. Ju, Y. Fan, S. Gras. B. J. J. Slagmolen, H. Miao, P. Barriga D.G. Blair, D. J. Hosken, A. F. Brooks, P. J. Veitch, D. Mudge, J. Munch (Submitted on 8 Jan 2008) 10 pages and 5 figures We report the first observation of three-mode opto-acoustic parametric interactions of the type predicted to cause parametric instabilities in an 80 m long, high optical power cavity that uses suspended sapphire mirrors. Resonant interaction occurs between two distinct optical modes and an acoustic mode of one mirror when the difference in frequency between the two optical cavity modes is close to the frequency of the acoustic mode. Experimental results validate the theory of parametric instability in high power optical cavities. ----------------------------------------------------------------------------- arXiv:0802.0582v1 [astro-ph] Astrodynamical Space Test of Relativity using Optical Devices I (ASTROD I) - A class-M fundamental physics mission proposal for Cosmic Vision 2015-2025 Authors: Thierry Appourchaux, Raymond Burston, Yanbei Chen, Michael Cruise, Hansjoerg Dittus, Bernard Foulon, Patrick Gill, Laurent Gizon, Hugh Klein, Sergei Klioner, Sergei Kopeikin, Hans Krueger, Claus Laemmerzahl, Alberto Lobo, Xinlian Luo, Helen Margolis, Wei-Tou Ni, Antonio Pulido Paton, Qiuhe Peng, Achim Peters, Ernst Rasel, Albrecht Ruediger, Etienne Samain, Hanns Selig, Diana Shaul, Timothy Sumner, Stephan Theil, Pierre Touboul, Slava Turyshev, Haitao Wang, Li Wang, Linqing Wen, Andreas Wicht, Ji Wu, Xiaomin Zhang, Cheng Zhao (Submitted on 5 Feb 2008) 26 pages, 11 figures, shortened from the original cosmic vision proposal, submitted to Experimental Astronomy ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test General Relativity with an improvement in sensitivity of over 3 orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is an international project, with major contributions from Europe and China and is envisaged as the first in a series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals. A second mission, ASTROD II is envisaged as a three-spacecraft mission which would test General Relativity to one part per billion, enable detection of solar g-modes, measure the solar Lense-Thirring effect to 10 parts per million, and probe gravitational waves at frequencies below the LISA bandwidth. In the third phase (ASTROD III or Super-ASTROD), larger orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below the ASTROD II bandwidth. ----------------------------------------------------------------------------- arXiv:0804.0332v1 The Effect of Higher Harmonic Corrections on the Detection of massive black hole binaries with LISA Authors: Edward K. Porter, Neil J. Cornish (Submitted on 2 Apr 2008) 15 pages, 8 figures, submitted to PRD Massive black hole binaries are key targets for the space based gravitational wave interferometer LISA. Several studies have investigated how LISA observations could be used to constrain the parameters of these systems. Until recently, most of these studies have ignored the higher harmonic corrections to the waveforms. Here we analyze the effects of the higher harmonics in more detail by performing extensive Monte Carlo simulations. We pay particular attention to how the higher harmonics impact parameter correlations, and show that the additional harmonics help mitigate the impact of having two laser links fail, by allowing for an instantaneous measurement of the gravitational wave polarization with a single interferometer channel. By looking at parameter correlations we are able to explain why certain mass ratios provide dramatic improvements in certain parameter estimations, and illustrate how the improved polarization measurement improves the prospects for single interferometer operation. ----------------------------------------------------------------------------- arXiv:0804.3323v2 Detection Strategies for Extreme Mass Ratio Inspirals Authors: N. J. Cornish (Submitted on 21 Apr 2008 (v1), last revised 5 Aug 2008 (this version, v2)) 6 pages, 4 figures The capture of compact stellar remnants by galactic black holes provides a unique laboratory for exploring the near horizon geometry of the Kerr spacetime, or possible departures from general relativity if the central cores prove not to be black holes. The gravitational radiation produced by these Extreme Mass Ratio Inspirals (EMRIs) encodes a detailed map of the black hole geometry, and the detection and characterization of these signals is a major scientific goal for the LISA mission. The waveforms produced are very complex, and the signals need to be coherently tracked for hundreds to thousands of cycles to produce a detection, making EMRI signals one of the most challenging data analysis problems in all of gravitational wave astronomy. Estimates for the number of templates required to perform an exhaustive grid-based matched-filter search for these signals are astronomically large, and far out of reach of current computational resources. Here a hierarchical approach to the EMRI detection problem is developed that employs a directed-stochastic search technique. The algorithm, dubbed Metropolis Hastings Monte Carlo (MHMC), is closely related to Markov Chain Monte Carlo and genetic algorithms. The utility of the MHMC approach is demonstrated using simulated data sets from the Mock LISA Data Challenge. ----------------------------------------------------------------------------- arXiv:0806.2110v1 The Mock LISA Data Challenges: from Challenge 1B to Challenge 3 Authors: Stanislav Babak, John G. Baker, Matthew J. Benacquista, Neil J. Cornish, Jeff Crowder, Shane L. Larson, Eric Plagnol, Edward K. Porter, Michele Vallisneri, Alberto Vecchio (the Mock LISA Data Challenge Task Force), Keith Arnaud, Leor Barack, Arkadiusz Blaut, Curt Cutler, Stephen Fairhurst, Jonathan Gair, Xuefei Gong, Ian Harry, Deepak Khurana, Andrzej Królak, Ilya Mandel, Reinhard Prix, B. S. Sathyaprakash, Pavlin Savov, Yu Shang, Miquel Trias, John Veitch, Yan Wang, Linqing Wen, John T. Whelan (the Challenge 1B participants) (Submitted on 12 Jun 2008) 20 pages, 3 EPS figures. Proceedings of the 12th Gravitational Wave Data Analysis Workshop, Cambridge MA, 13--16 December 2007 The Mock LISA Data Challenges are a programme to demonstrate and encourage the development of LISA data-analysis capabilities, tools and techniques. At the time of this workshop, three rounds of challenges had been completed, and the next was about to start. In this article we provide a critical analysis of entries to the latest completed round, Challenge 1B. The entries confirm the consolidation of a range of data-analysis techniques for Galactic and massive--black-hole binaries, and they include the first convincing examples of detection and parameter estimation of extreme-mass -ratio inspiral sources. In this article we also introduce the next round, Challenge 3. Its data sets feature more realistic waveform models (e.g., Galactic binaries may now chirp, and massive--black-hole binaries may precess due to spin interactions), as well as new source classes (bursts from cosmic strings, isotropic stochastic backgrounds) and more complicated nonsymmetric instrument noise. Journal reference: Class.Quant.Grav.25:184026,2008 ----------------------------------------------------------------------------- arXiv:0811.1011v1 Massive Black Hole Binary Inspirals: Results from the LISA Parameter Estimation Taskforce Authors: K. G. Arun, Stas Babak, Emanuele Berti, Neil Cornish, Curt Cutler, Jonathan Gair, Scott A. Hughes, Bala R. Iyer, Ryan N. Lang, Ilya Mandel, Edward K. Porter, Bangalore S. Sathyaprakash, Siddhartha Sinha, Alicia M. Sintes, Miquel Trias, Chris Van Den Broeck, Marta Volonteri (Submitted on 6 Nov 2008) 14 pages, 2 figures, 5 tables, submitted to proceedings of 7th LISA Symposium. The LISA Parameter Estimation (LISAPE) Taskforce was formed in September 2007 to provide the LISA Project with vetted codes, source distribution models, and results related to parameter estimation. The Taskforce's goal is to be able to quickly calculate the impact of any mission design changes on LISA's science capabilities, based on reasonable estimates of the distribution of astrophysical sources in the universe. This paper describes our Taskforce's work on massive black-hole binaries (MBHBs). Given present uncertainties in the formation history of MBHBs, we adopt four different population models, based on (i) whether the initial black- hole seeds are small or large, and (ii) whether accretion is efficient or inefficient at spinning up the holes. We compare four largely independent codes for calculating LISA's parameter-estimation capabilities. All codes are based on the Fisher-matrix approximation, but in the past they used somewhat different signal models, source parametrizations and noise curves. We show that once these differences are removed, the four codes give results in extremely close agreement with each other. Using a code that includes both spin precession and higher harmonics in the gravitational- wave signal, we carry out Monte Carlo simulations and determine the number of events that can be detected and accurately localized in our four population models. ----------------------------------------------------------------------------- arXiv:0811.2814v2 Semi-classical limit and minimum decoherence in the Conditional Probability Interpretation of Quantum Mechanics Authors: Vincent Corbin, Neil J. Cornish (Submitted on 17 Nov 2008 (v1), last revised 2 Dec 2008 (this version, v2)) 8 pages The Conditional Probability Interpretation of Quantum Mechanics replaces the abstract notion of time used in standard Quantum Mechanics by the time that can be read off from a physical clock. The use of physical clocks leads to apparent non-unitary and decoherence. Here we show that a close approximation to standard Quantum Mechanics can be recovered from conditional Quantum Mechanics for semi-classical clocks, and we use these clocks to compute the minimum decoherence predicted by the Conditional Probability Interpretation. ----------------------------------------------------------------------------- arXiv:0807.2045v1 Using the etalon effect for in-situ balancing of the Advanced Virgo arm cavities Authors: S. Hild, A. Freise, M. Mantovani, S. Chelkowski, J. Degallaix, R. Schilling (Submitted on 13 Jul 2008) 12 pages, 6 Figures Several large-scale interferometric gravitational-wave detectors use resonant arm cavities to enhance the light power in the interferometer arms. These cavities are based on different optical designs: One design uses wedged input mirrors to create additional optical pick-off ports for deriving control signals. The second design employs input mirrors without wedge and thus offers the possibility to use the etalon effect inside the input mirrors for tuning the finesse of the arm cavities. In this article we introduce a concept of maximized flexibility that combines both of these options, by featuring wedges at the input mirrors and using the etalon effect instead in the end mirrors. We present a design for the arm cavities of Advanced Virgo. We have used numerical simulations to derive requirements for the manufacturing accuracy of an end mirror etalon for Advanced Virgo. Furthermore, we give analytical approximations for the achievable tuning range of the etalon in dependence on the reflectance, the curvature and the orientation of the etalon back surface. ----------------------------------------------------------------------------- arXiv:0811.3242v1 DC-readout of a signal-recycled gravitational wave detector Authors: S.Hild, H.Grote, J.Degallaix, S.Chelkowski, K.Danzmann, A. Freise, M.Hewitson, J.Hough, H.Lueck, M.Prijatelj, K.A.Strain, J.R.Smith, B.Willke (Submitted on 19 Nov 2008) 11 pages All first-generation large-scale gravitational wave detectors are operated at the dark fringe and use a heterodyne readout employing radio frequency (RF) modulation-demodulation techniques. However, the experience in the currently running interferometers reveals several problems connected with a heterodyne readout, of which phase noise of the RF modulation is the most serious one. A homodyne detection scheme (DC-readout), using the highly stabilized and filtered carrier light as local oscillator for the readout, is considered to be a favourable alternative. Recently a DC- readout scheme was implemented on the GEO 600 detector. We describe the results of first measurements and give a comparison of the performance achieved with homodyne and heterodyne readout. The implications of the combined use of DC-readout and signal-recycling are considered. ----------------------------------------------------------------------------- arXiv:0807.3041v2 A Kirchhoff-like conservation law in Regge calculus Authors: Adrian P. Gentle, Arkady Kheyfets, Jonathan R. McDonald, Warner A. Miller (Submitted on 18 Jul 2008 (v1), last revised 22 Jul 2008 (this version, v2)) 13 pages, 4 figures, submitted to Class. Quantum Grav Simplicial lattices provide an elegant framework for discrete spacetimes. The inherent orthogonality between a simplicial lattice and its circumcentric dual yields an austere representation of spacetime which provides a conceptually simple form of Einstein's geometric theory of gravitation. A sufficient understanding of simplicial spacetimes has been demonstrated in the literature for spacetimes devoid of all non- gravitational sources. However, this understanding has not been adequately extended to non-vacuum spacetime models. Consequently, a deep understanding of the diffeomorphic structure of the discrete theory is lacking. Conservation laws and symmetry properties are attractive starting points for coupling matter with the lattice. We present a simplicial form of the contracted Bianchi identities which is based on the E. Cartan moment of rotation operator. These identities manifest themselves in the conceptually-simple form of a Kirchhoff-like conservation law. This conservation law enables one to extend Regge Calculus to non-vacuum spacetimes, and provides a deeper understanding of the simplicial diffeomorphism group. ----------------------------------------------------------------------------- arXiv:0712.3833v2 [astro-ph] Redshift periodicity in quasar number counts from Sloan Digital Sky Survey Authors: John G. Hartnett (Submitted on 22 Dec 2007 (v1), last revised 8 Feb 2008 (this version, v2)) 9 pages, 3 figures Fourier spectral analysis has been carried out on the quasar number count as a function of redshift calculated from the quasar data of the Sloan Digital Sky Survey DR6 data release. The results indicate that quasars have preferred periodic redshifts with redshift intervals of 0.258, 0.312, 0.44, 0.63, and 1.1. Within their standard errors these intervals are integer multiples 4, 5, 7, 10 and 20 of 0.062. Could this be indicative of an intrinsic redshift for quasars as has been suggested by some? ----------------------------------------------------------------------------- arXiv:0809.0334v1 [astro-ph] Pressure gradients, shell crossing singularities and acoustic oscillations - application to inhomogeneous cosmological models Authors: Krzysztof Bolejko, Paul Lasky (Submitted on 2 Sep 2008) 5 pages, 3 figures Inhomogeneous cosmological models have recently become a very interesting alternative to standard cosmology. This is because these models are able to fit cosmological observations without the need for dark energy. However, due to inhomogeneity and pressure-less matter content, these models can suffer from shell crossing singularities. These singularities occur when two shell of dust collide with each other leading to infinite values of the density. In this Letter we show that if inhomogeneous pressure is included then these singularities can be prevented from occurring over the period of structure formation. Thus, a simple incorporation of a gradient of pressure allows for more comprehensive studies of inhomogeneous cosmological models and their application to cosmology. Journal reference: MNRAS 391, L59 (2008) ----------------------------------------------------------------------------- arXiv:0811.2006v1 [astro-ph] Structure of Neutron Stars in Tensor-Vector-Scalar Theory Authors: Paul D. Lasky, Hajime Sotani, Dimitrios Giannios (Submitted on 12 Nov 2008) Bekenstein's Tensor-Vector-Scalar (TeVeS) theory has had considerable success in explaining various phenomena without the need for dark matter. However, it is difficult to observationally discern the differences between TeVeS and predictions made within the Lambda-cold dark matter concordance model. This implies that alternative tests are required that independently verify which theory is correct. For this we turn to the strong-field regime of TeVeS. In particular, we solve the spherically symmetric equations of hydrostatic equilibrium for a perfect fluid with a realistic equation of state to build models of neutron stars in TeVeS. We show that causality within the neutron star is only maintained for certain cosmological values of the scalar field, which allows us to put constraints on this value independently of cosmological observations. We also discuss in detail the internal structure of neutron stars and how each of the free parameters in the theory effects the overall size and mass of the neutron stars. In particular, the radii of neutron stars in TeVeS can significantly differ from those in General Relativity for certain values of the vector field coupling, which allows us to also place extra constraints on this parameter. Finally, we discuss future observations of neutron stars using both the electromagnetic and gravitational wave spectrums that will allow for tests of the appropriate theory of gravity. Journal reference: Phys. Rev. D 78 (2008) 104019 ----------------------------------------------------------------------------- arXiv:0802.4118v1 [quant-ph] A Quantum-Enhanced Prototype Gravitational-Wave Detector Authors: Keisuke Goda, Osamu Miyakawa, Eugeniy E. Mikhailov, Shailendhar Saraf, Rana Adhikari, Kirk McKenzie, Robert Ward, Steve Vass, Alan J. Weinstein, Nergis Mavalvala (Submitted on 28 Feb 2008) 7 pages, 3 figures. Accepted for publication in Nature Physics The quantum nature of the electromagnetic field imposes a fundamental limit on the sensitivity of optical precision measurements such as spectroscopy, microscopy, and interferometry. The so-called quantum limit is set by the zero-point fluctuations of the electromagnetic field, which constrain the precision with which optical signals can be measured. In the world of precision measurement, laser-interferometric gravitational wave (GW) detectors are the most sensitive position meters ever operated, capable of measuring distance changes on the order of 10^-18 m RMS over kilometer separations caused by GWs from astronomical sources. The sensitivity of currently operational and future GW detectors is limited by quantum optical noise. Here we demonstrate a 44% improvement in displacement sensitivity of a prototype GW detector with suspended quasi-free mirrors at frequencies where the sensitivity is shot-noise- limited, by injection of a squeezed state of light. This demonstration is a critical step toward implementation of squeezing-enhancement in large-scale GW detectors. ----------------------------------------------------------------------------- arXiv:0809.4352v1 Gravitational radiation from pulsar glitches Authors: C. A. van Eysden, A. Melatos (Submitted on 25 Sep 2008) 28 pages The nonaxisymmetric Ekman flow excited inside a neutron star following a rotational glitch is calculated analytically including stratification and compressibility. For the largest glitches, the gravitational wave strain produced by the hydrodynamic mass quadrupole moment approaches the sensitivity range of advanced long-baseline interferometers. It is shown that the viscosity, compressibility, and orientation of the star can be inferred in principle from the width and amplitude ratios of the Fourier peaks (at the spin frequency and its first harmonic) observed in the gravitational wave spectrum in the plus and cross polarizations. These transport coefficients constrain the equation of state of bulk nuclear matter, because they depend sensitively on the degree of superfluidity. ----------------------------------------------------------------------------- arXiv:0802.3422v1 Black Holes without Event Horizons Authors: Alex B. Nielsen (Submitted on 23 Feb 2008) Talk at APCTP Winter School, Daejeon, Korea, 2008. 7 pages, no figures We discuss some of the drawbacks of using event horizons to define black holes. The reasons are both practical, physical and theoretical. We argue that locally defined trapping horizons can remedy many of these drawbacks. We examine of the question of whether black hole thermodynamics should be associated with event horizons or trapping horizons. To this end we discuss what role trapping horizons may play in black hole thermodynamics. In addition, we show how trapping horizons may give rise to Hawking radiation and discuss the issue of gravitational entropy. ----------------------------------------------------------------------------- arXiv:0804.4435v1 Spherically symmetric trapping horizons, the Misner-Sharp mass and black hole evaporation Authors: Alex B. Nielsen, Dong-han Yeom (Submitted on 28 Apr 2008) 9 pages, 10 figures Understood in terms of pure states evolving into mixed states, the possibility of information loss in black holes is closely related to the global causal structure of spacetime, as is the existence of event horizons. However, black holes need not be defined by event horizons, and in fact we argue that in order to have a fully unitary evolution for black holes, they should be defined in terms of something else, such as a trapping horizon. The Misner-Sharp mass in spherical symmetry shows very simply how trapping horizons can give rise to black hole thermodynamics, Hawking radiation and singularities. We show how the Misner-Sharp mass can also be used to give insights into the process of collapse and evaporation of locally defined black holes. ----------------------------------------------------------------------------- arXiv:0809.1711v1 Black holes without boundaries Authors: Alex B. Nielsen (Submitted on 10 Sep 2008) 8 pages. Invited essay for special edition of the International Journal of Modern Physics D We discuss some of the drawbacks of using event horizons to define black holes and suggest ways in which black holes can be described without event horizons, using trapping horizons. We show that these trapping horizons give rise to thermodynamic behavior and possibly Hawking radiation too. This raises the issue of whether the event horizon or the trapping horizon should be seen as the true boundary of a black hole. This difference is important if we believe that quantum gravity will resolve the central singularity of the black hole and clarifies several of the issues associated with black hole thermodynamics and information loss. ----------------------------------------------------------------------------- arXiv:0801.4797v1 Geometrization of electromagnetism Authors: Nikodem J. Poplawski (Submitted on 30 Jan 2008) 8 pages A general affine connection has enough degrees of freedom to describe the classical gravitational and electromagnetic fields in the metric-affine formulation of gravity. The gravitational field is represented by the symmetric part of the Ricci tensor and the classical electromagnetic field can be represented geometrically by the tensor of homothetic curvature. The simplest metric-affine Lagrangian that depends on these two tensors is linear in the Ricci scalar and quadratic in the tensor of homothetic curvature, generating the Einstein-Maxwell equations. To include spinor fields we use the metric-affine variational principle with the tetrad and spin connection as dynamical variables. We show that the generally covariant Dirac Lagrangian gives rise to the standard spinor source for the Einstein-Maxwell equations, while the spinor field obeys the nonlinear Heisenberg-Ivanenko equation with the electromagnetic coupling. ----------------------------------------------------------------------------- arXiv:0802.4453v1 Geometrical formulation of classical electromagnetism Authors: Nikodem J. Poplawski (Submitted on 29 Feb 2008) 5 pages A general affine connection has enough degrees of freedom 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, while the classical electromagnetic field is represented geometrically by the tensor of homothetic curvature. We introduce matter as the four-velocity field subject to the kinematical constraint in which the Lagrange multiplier represents the energy density. A coupling between the four-velocity and the trace of the nonmetricity tensor represents the electric charge density. We show that the simplest metric-affine Lagrangian that depends on the Ricci tensor and the tensor of homothetic curvature generates the Einstein-Maxwell field equations, while the Bianchi identity gives the Lorentz equation of motion. If the four-velocity couples to the torsion vector, the Einstein equations are modified by a term that is significant at the Planck scale and may prevent the formation of spacetime singularities. ----------------------------------------------------------------------------- arXiv:0803.4366v1 Variational formulation of Eisenhart's unified theory Authors: Nikodem J. Poplawski (Submitted on 31 Mar 2008) 9 pages Eisenhart's unified field theory is based on a non-Riemannian affine connection related to the covariant derivative of the electromagnetic field tensor. The sourceless field equations of this theory arise from vanishing of the symmetrized Ricci tensor and the torsion trace. We formulate Eisenhart's theory from a metric-affine variational principle; a Lagrange multiplier constraining the torsion becomes the source for the Maxwell equations. ----------------------------------------------------------------------------- arXiv:0806.2283v1 On variational formulation of relativistic hydrodynamics Authors: Nikodem J. Poplawski (Submitted on 13 Jun 2008) 4 pages We combine Taub's and Ray's variational approaches to relativistic hydrodynamics of perfect fluids into a simple formulation. ----------------------------------------------------------------------------- arXiv:0712.0196v1 Robust Bayesian detection of unmodelled bursts Authors: Antony C Searle, Patrick J Sutton, Massimo Tinto, Graham Woan (Submitted on 2 Dec 2007) 9 pages, 1 figure, submitted to CQG Amaldi proceedings special issue A Bayesian treatment of the problem of detecting an unmodelled gravitational wave burst with a global network of gravitational wave observatories reveals that several previously proposed statistics have implicit biases that render them sub-optimal for realistic signal populations. Journal reference: Class.Quant.Grav.25:114038,2008 ----------------------------------------------------------------------------- arXiv:0804.1161v1 Monte-Carlo and Bayesian techniques in gravitational wave burst data analysis Authors: Antony C. Searle (Submitted on 7 Apr 2008) 9 pages, submitted to GWDAW12 proceedings Monte-Carlo simulations are used in the gravitational wave burst detection community to demonstrate and compare the properties of different search techniques. We note that every Monte-Carlo simulation has a corresponding optimal search technique according to both the non-Bayesian Neyman-Pearson criterion and the Bayesian approach, and that this optimal search technique is the Bayesian statistic. When practical, we recommend deriving the optimal statistic for a credible Monte-Carlo simulation, rather than testing ad hoc statistics against that simulation. ----------------------------------------------------------------------------- arXiv:0809.2809v1 Bayesian detection of unmodeled bursts of gravitational waves Authors: Antony C. Searle, Patrick J. Sutton, Massimo Tinto (Submitted on 16 Sep 2008) 14 pages, 4 figures The data analysis problem of coherently searching for unmodeled gravitational-wave bursts in the data generated by a global network of gravitational-wave observatories has been at the center of research for almost two decades. As data from these detectors is starting to be analyzed, a renewed interest in this problem has been sparked. A Bayesian approach to the problem of coherently searching for gravitational wave bursts with a network of ground-based interferometers is here presented. We demonstrate how to systematically incorporate prior information on the burst signal and its source into the analysis. This information may range from the very minimal, such as best-guess durations, bandwidths, or polarization content, to complete prior knowledge of the signal waveforms and the distribution of sources through spacetime. We show that this comprehensive Bayesian formulation contains several previously proposed detection statistics as special (unphysical) limiting cases, and demonstrate that it outperforms them. ----------------------------------------------------------------------------- arXiv:0712.0427v1 Analogue spacetimes: Toy models for "quantum gravity'' Authors: Matt Visser (Victoria University of Wellington), Silke Weinfurtner (Victoria University of Wellington) (Submitted on 4 Dec 2007) 24 pages; Based on a talk at the conference: From Quantum to Emergent Gravity: Theory and Phenomenology, June 11-15 2007, Trieste, Italy Why are "analogue spacetimes'' interesting? For the purposes of this workshop the answer is simple: Analogue spacetimes provide one with physically well-defined and physically well-understood concrete models of many of the phenomena that seem to be part of the yet incomplete theory of "quantum gravity'', or more accessibly, "quantum gravity phenomenology''. Indeed "analogue spacetimes'' provide one with concrete models of "emergence'' (whereby the effective low-energy theory can be radically different from the high-energy microphysics). They also provide many concrete and controlled models of "Lorentz symmetry breaking'', and extensions of the usual notions of pseudo-Riemannian geometry such as "rainbow spacetimes'', and pseudo-Finsler geometries, and more. I will provide an overview of the key items of "unusual physics'' that arise in analogue spacetimes, and argue that they provide us with hints of what we should be looking for in any putative theory of "quantum gravity''. For example: The dispersion relations that naturally arise in the known emergent/analogue spacetimes typically violate analogue Lorentz invariance at high energy, but do not do so in completely arbitrary manner. This suggests that a search for arbitrary violations of Lorentz invariance is possibly overkill: There are a number of natural and physically well-motivated restrictions one can put on emergent/ analogue dispersion relations, considerably reducing the plausible parameter space. Journal reference: PoSQG-Ph:042,2007 ----------------------------------------------------------------------------- arXiv:0712.1619v1 Cosmodynamics: Energy conditions, Hubble bounds, density bounds, time and distance bounds Authors: Celine Cattoen (Victoria University of Wellington), Matt Visser (Victoria University of Wellington) (Submitted on 10 Dec 2007) 21 pages, 2 figures We refine and extend a programme initiated by one of the current authors [Science 276 (1997) 88; Phys. Rev. D56 (1997) 7578] advocating the use of the classical energy conditions of general relativity in a cosmological setting to place very general bounds on various cosmological parameters. We show how the energy conditions can be used to bound the Hubble parameter H(z), Omega parameter Omega(z), density rho(z), distance d(z), and lookback time T(z) as (relatively) simple functions of the redshift z, present-epoch Hubble parameter H_0, and present-epoch Omega parameter Omega_0. We compare these results with related observations in the literature, and confront the bounds with the recent supernova data. Journal reference: Class.Quant.Grav.25:165013,2008 ----------------------------------------------------------------------------- arXiv:0801.2673v1 Cosmological particle production in emergent rainbow spacetimes Authors: Silke Weinfurtner, Piyush Jain, Matt Visser, C.W. Gardiner (Submitted on 17 Jan 2008) We investigate cosmological particle production in spacetimes where Lorentz invariance emerges in the infrared limit, but is explicitly broken in the ultraviolet regime. Our specific model focuses on the boost subgroup that supports CPT invariance and results in a momentum-dependent dispersion relation. Motivated by previous studies on spacetimes emerging from a microscopic substrate, we show how these modifications naturally lead to momentum-dependent rainbow metrics. Firstly, we investigate the possibility of reproducing cosmological particle production in spacetimes emerging from real Bose gases. We have studied the influence of non-perturbative ultraviolet corrections in time-dependent analogue spacetimes, leading to momentum-dependent emergent rainbow spacetimes. Within certain limits the analogy is sufficiently good to simulate relativistic quantum field theory in time-dependent classical backgrounds, and the quantum effects are approximately robust against the model-dependent modifications. Secondly, we analyze how significantly the particle production process deviates from the common picture. While very low-energy modes do not see the difference at all, some modes "re-enter the Hubble horizon" during the inflationary epoch, and extreme ultraviolet modes are completely insensitive to the expansion. ----------------------------------------------------------------------------- arXiv:0804.1346v1 On the phenomenon of emergent spacetimes: An instruction guide for experimental cosmology Authors: Silke Weinfurtner (University of British Columbia), Matt Visser (Victoria University of Wellington), Piyush Jain (University of Otago), C.W. Gardiner (University of Otago) (Submitted on 8 Apr 2008) 19 pages; Based on a talk at the conference: From Quantum to Emergent Gravity: Theory and Phenomenology, June 11-15 2007, Trieste, Italy We present a toy model where spacetime is emergent from a more fundamental microscopic system, and investigate the gray area interpolating between the collective and free-particle regimes. For a period of rapid exponential growth in the analogue universe, we argue that the intermediate regime is best described by a coloured potpourri of geometries -- a "rainbow geometry". This can be viewed as an alternative approach towards understanding quantum field theories in the presence of Lorentz-symmetry breaking at ultraviolet scales. Firstly, it is pointed out that cosmological particle production in our emergent FRW-type analogue universe, when compared to conventional semi-classical quantum gravity, is only temporarily robust against model-specific deviations from Lorentz invariance. Secondly, it is possible to carry out a straightforward quantitative analysis to estimate a suitable parameter regime for experimental (analogue) cosmology. Journal reference: PoSQG-Ph:044,2007 ----------------------------------------------------------------------------- arXiv:0806.0950v1 The pseudo-Finslerian spacetimes of birefringent optics Authors: Jozef Skakala (Victoria University of Wellington), Matt Visser (Victoria University of Wellington) (Submitted on 5 Jun 2008) 19 pages It is reasonably well-known that birefringent crystal optics can to some extent be described by the use of pseudo-Finslerian spacetimes (an extension of pseudo-Riemannian spacetime). What is less commonly appreciated is that there are two separate and quite disjoint pseudo- Finsler structures for the two photon polarizations, and further, that there are separate tangent-space pseudo-Finsler structures defined by the group velocity and co-tangent-space pseudo-co-Finsler structures defined by the phase velocity. The inter-connections between these four separate pseudo-Finsler structures are rather subtle. One particular source of technical difficulty is the fact that because physicists need to use pseudo-Finsler structures to describe propagation of signals, there will be nonzero null vectors in both the tangent and cotangent spaces -- this causes significant problems in that many of the mathematical results normally obtained for "usual'' (Euclidean signature) Finsler structures either do not apply, or require significant modifications to their formulation. We shall first provide a few basic definitions, and then present a tutorial outline of the relevant physics of birefringent optics, explicitly demonstrating the interpretation in terms of pseudo-Finsler spacetimes. We shall then discuss the tricky issues that arise when trying to inter-relate the various pseudo-Finsler structures we encounter, and finish by connecting these technical questions (which of course arise in what is a physically a very well-understood situation) back to ongoing research into possible extensions and modifications of general relativity. ----------------------------------------------------------------------------- arXiv:0806.2186v1 Bounding the Hubble flow in terms of the w parameter Authors: Celine Cattoen (Victoria University of Wellington), Matt Visser (Victoria University of Wellington) (Submitted on 13 Jun 2008) 15 pages The last decade has seen increasing efforts to circumscribe and bound the cosmological Hubble flow in terms of model-independent constraints on the cosmological fluid - such as, for instance, the classical energy conditions of general relativity. Quite a bit can certainly be said in this regard, but much more refined bounds can be obtained by placing more precise constraints (either theoretical or observational) on the cosmological fluid. In particular, the use of the w-parameter (w=p/rho) has become increasingly common as a surrogate for trying to say something about the cosmological equation of state. Herein we explore the extent to which a constraint on the w-parameter leads to useful and nontrivial constraints on the Hubble flow, in terms of constraints on density rho(z), Hubble parameter H(z), density parameter Omega(z), cosmological distances d(z), and lookback time T(z). In contrast to other partial results in the literature, we carry out the computations for arbitrary values of the space curvature k in [-1,0,+1], equivalently for arbitrary Omega_0 <= 1. Journal reference: JCAP11(2008)024 ----------------------------------------------------------------------------- arXiv:0806.2209v2 Bounding the greybody factors for Schwarzschild black holes Authors: Petarpa Boonserm (Victoria University of Wellington), Matt Visser (Victoria University of Wellington) (Submitted on 13 Jun 2008 (v1), last revised 23 Jun 2008 (this version, v2)) 5 pages Greybody factors in black hole physics modify the naive Planckian spectrum that is predicted for Hawking radiation when working in the limit of geometrical optics. We consider the Schwarzschild geometry in (3+1) dimensions, and analyze the Regge-Wheeler equation for arbitrary particle spin S and wave-mode angular momentum L, deriving rigourous bounds on the greybody factors as a function of S, L, wave frequency (omega), and the black hole mass, m. Journal reference: Phys.Rev.D78:101502,2008 ----------------------------------------------------------------------------- arXiv:0808.1931v1 Quantum Interest in (3+1) dimensional Minkowski space Authors: Gabriel Abreu (Victoria University of Wellington), Matt Visser (Victoria University of Wellington) (Submitted on 14 Aug 2008) 8 pages The so-called "Quantum Inequalities", and the "Quantum Interest Conjecture", use quantum field theory to impose significant restrictions on the temporal distribution of the energy density measured by a time-like observer, potentially preventing the existence of exotic phenomena such as "Alcubierre warp-drives" or "traversable wormholes". Both the quantum inequalities and the quantum interest conjecture can be reduced to statements concerning the existence or non-existence of bound states for a certain one-dimensional quantum mechanical pseudo-Hamiltonian. Using this approach, we shall provide a simple proof of one version of the Quantum Interest Conjecture in (3+1) dimensional Minkowski space. ----------------------------------------------------------------------------- arXiv:0808.2068v1 Explicit form of the Mann-Marolf surface term in (3+1) dimensions Authors: Matt Visser (Victoria University of Wellington) (Submitted on 14 Aug 2008) 4 pages The Mann-Marolf surface term is a specific candidate for the "reference background term" that is to be subtracted from the Gibbons-Hawking surface term in order make the total gravitational action of asymptotically flat spacetimes finite. That is, the total gravitational action is taken to be: (Einstein-Hilbert bulk term) + (Gibbons-Hawking surface term) - (Mann-Marolf surface term). As presented by Mann and Marolf, their surface term is specified implicitly in terms of the Ricci tensor of the boundary. Herein I demonstrate that for the physically interesting case of a (3+1) dimensional bulk spacetime, the Mann-Marolf surface term can be specified explicitly in terms of the Einstein tensor of the (2+1) dimensional boundary. ----------------------------------------------------------------------------- arXiv:0809.0537v1 Cosmographic Hubble fits to the supernova data Authors: Celine Cattoen (Victoria University of Wellington), Matt Visser (Victoria University of Wellington) (Submitted on 3 Sep 2008) 28 pages The Hubble relation between distance and redshift is a purely cosmographic relation that depends only on the symmetries of a FLRW spacetime, but does not intrinsically make any dynamical assumptions. This suggests that it should be possible to estimate the parameters defining the Hubble relation without making any dynamical assumptions. To test this idea, we perform a number of inter-related cosmographic fits to the legacy05 and gold06 supernova datasets. Based on this supernova data, the "preponderance of evidence" certainly suggests an accelerating universe. However we would argue that (unless one uses additional dynamical and observational information) this conclusion is not currently supported "beyond reasonable doubt". As part of the analysis we develop two particularly transparent graphical representations of the redshift-distance relation - representations in which acceleration versus deceleration reduces to the question of whether the relevant graph slopes up or down. 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 or other suitable distance surrogate. Second, the fitted value for the deceleration parameter changes 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 supernova data should be treated with some caution. Journal reference: Phys.Rev.D78:063501,2008 ----------------------------------------------------------------------------- arXiv:0809.0907v1 Traversable wormholes: Some simple examples Authors: Matt Visser (Victoria University of Wellington) (Submitted on 4 Sep 2008) Pre-arXiv article from 1989; 7 pages, no figures. Building on the work of Morris, Thorne, and Yurtsever, some particularly simple examples of traversable wormholes are exhibited. These examples are notable both because the analysis is not limited to spherically symmetric cases, and because it is possible to in some sense minimize the use of exotic matter. In particular, it is possible for a traveller to traverse such a wormhole without passing through a region of exotic matter. As in previous analyses, the weak energy condition is violated in these traversable wormholes. Journal reference: Phys.Rev.D39:3182-3184,1989 ----------------------------------------------------------------------------- arXiv:0809.0927v1 Traversable wormholes from surgically modified Schwarzschild spacetimes Authors: Matt Visser (Victoria University of Wellington) (Submitted on 4 Sep 2008) Pre-arXiv article from 1989; 12 pages, no figures. In this paper I present a new class of traversable wormholes. This is done by surgically grafting two Schwarzschild spacetimes together in such a way that no event horizon is permitted to form. This surgery concentrates a non--zero stress--energy on the boundary layer between the two asymptotically flat regions. I shall investigate this stress- energy in detail using the "junction condition" formalism. A feature of the present analysis is that this class of traversable wormholes is sufficiently simple for a (partial) dynamical stability analysis to be carried out. The stability analysis places constraints on the equation of state of the exotic matter that comprises the throat of the wormhole. Journal reference: Nucl.Phys.B328:203-212,1989 ----------------------------------------------------------------------------- arXiv:0810.4376v1 Birefringence in pseudo-Finsler spacetimes Authors: Jozef Skakala (Victoria University of Wellington), Matt Visser (Victoria University of Wellington) (Submitted on 24 Oct 2008) 8 pages; Talk delivered by Jozef Skakala at the NEB XIII conference, (Recent Developments in Gravity), Thessalonika, Greece, June 2008 Based on the analogue spacetime programme, and many other ideas currently mooted in "quantum gravity", there is considerable ongoing speculation thatthe usual pseudo-Riemannian (Lorentzian) manifolds of general relativity might eventually be modified at short distances. Two specific modifications that are often advocated are the adoption of Finsler geometries (or more specifically, pseudo-Finsler spacetimes) and the possibility of birefringence (or more generally, multi-refringence). We have investigated the possibility of whether it is possible to usefully and cleanly deal with these two possibilities simultaneously. That is, given two (or more) "signal cones": Is it possible to naturally and intuitively construct a "unified" pseudo-Finsler spacetime such that the pseudo-Finsler metric is null on these "signal cones", but has no other zeros or singularities? Our results are much less encouraging than we had originally hoped, and suggest that while pseudo-Finsler spacetimes are certainly useful constructs, it is physically more appropriate to think of physics as taking place in a single topological manifold that carries several distinct pseudo-Finsler metrics, one for each polarization mode. ----------------------------------------------------------------------------- arXiv:0807.1710v2 Dynamical Analysis of the Structure of Neutron Star Critical Collapses Authors: M.-B. Wan, K.-J. Jin, W.-M. Suen (Submitted on 10 Jul 2008 (v1), last revised 10 Jul 2008 (this version, v2)) Poster version presented at the "2nd Course of the International School on Astrophysical Relativity", Erice, Italy, June 27th - July 5th in et al reported that axisymmetric simulations of NS-like objects with polytropic EOS undergo critical gravitational collapse. As the critical collapse observed via fine-tuning of the adiabatic index $\Gamma$, they conjecture that critical phenomena may occur in realistic astrophysical scenarios. To clarify the implications this numerical observation has on realistic astrophysical scenarios, here, we perform dynamical analysis on the structure of the critical collapse observed in the former work. We report the time scales and oscillation frequencies exhibited by the critical solution and compare these results with values obtained from analytic perturbative mode analysis of equilibrium TOV configurations. We also establish the universality of the critical solution with respect to a 1-parameter family of initial data as well as the phase space manifold of the critical collapse. ----------------------------------------------------------------------------- arXiv:0810.2631v1 The fluid/gravity correspondence: Lectures notes from the 2008 Summer School on Particles, Fields, and Strings Authors: Nicola Ambrosetti, James Charbonneau, Silke Weinfurtner (Submitted on 15 Oct 2008) 21 pages, 5 figures This is a paper compiled by students of the 2008 Summer School on Particles, Fields, and Strings held at the University of British Columbia on lectures given by Veronika Hubeny as understood and interpreted by the authors. We start with an introduction to the AdS/CFT duality. More specifically, we discuss the correspondence between relativistic, conformal hydrodynamics and Einstein's theory of gravity. Within our framework the Einstein equations are an effective description for the string theory in the bulk of AdS_5 spacetime and the hydrodynamic fluid equations represent the conformal field theory near thermal equilibrium on the boundary. In particular we present a new technique for calculating properties in fluid dynamics using the stress- energy tensor induced on the boundary, by the gravitational field in the bulk, and comparing it with the form of the stress-energy tensor from hydrodynamics. A detailed treatment can be found in [JHEP 02 (2008) 045] and [arXiv:0803.2526]. ----------------------------------------------------------------------------- arXiv:0712.3982v1 Gravitational energy and cosmic acceleration Authors: David L. Wiltshire (Submitted on 24 Dec 2007) 9 pages, 2 figures. An essay which received Honorable Mention in the 2007 GRF Essay Competition. Cosmic acceleration is explained quantitatively, as an apparent effect due to gravitational energy differences that arise in the decoupling of bound systems from the global expansion of the universe. "Dark energy" is a misidentification of those aspects of gravitational energy which by virtue of the equivalence principle cannot be localised, namely gradients in the energy due to the expansion of space and spatial curvature variations in an inhomogeneous universe. A new scheme for cosmological averaging is proposed which solves the Sandage-de Vaucouleurs paradox. Concordance parameters fit supernovae luminosity distances, the angular scale of the sound horizon in the CMB anisotropies, and the effective comoving baryon acoustic oscillation scale seen in galaxy clustering statistics. Key observational anomalies are potentially resolved, and unique predictions made, including a quantifiable variance in the Hubble flow below the scale of apparent homogeneity. Journal reference: Int.J.Mod.Phys.D17:641-649,2008 ----------------------------------------------------------------------------- arXiv:0712.3984v1 [astro-ph] Dark energy without dark energy Authors: David L. Wiltshire (Submitted on 24 Dec 2007) 32 pages, 8 figures An overview is presented of a recently proposed "radically conservative" solution to the problem of dark energy in cosmology. The proposal yields a model universe which appears to be quantitatively viable, in terms of its fit to supernovae luminosity distances, the angular scale of the sound horizon in the cosmic microwave background (CMB) anisotropy spectrum, and the baryon acoustic oscillation scale. It may simultaneously resolve key anomalies relating to primordial lithium abundances, CMB ellipticity, the expansion age of the universe and the Hubble bubble feature. The model uses only general relativity, and matter obeying the strong energy condition, but revisits operational issues in interpreting average measurements in our presently inhomogeneous universe, from first principles. The present overview examines both the foundational issues concerning the definition of gravitational energy in a dynamically expanding space, the quantitative predictions of the new model and its best-fit cosmological parameters, and the prospects for an era of new observational tests in cosmology. Journal reference: In "Dark Matter in Astroparticle and Particle Physics: Proceedings of the 6th International Heidelberg Conference", eds H.V. Klapdor-Kleingrothaus and G.F. Lewis, (World Scientific, Singapore, 2008) pp 565-596 ----------------------------------------------------------------------------- arXiv:0809.1183v3 Cosmological equivalence principle and the weak-field limit Authors: David L. Wiltshire (Submitted on 8 Sep 2008 (v1), last revised 24 Oct 2008 (this version, v3)) 17 pages, 5 figures he strong equivalence principle is extended in application to averaged dynamical fields in cosmology to include the role of the average density in the determination of inertial frames. The resulting cosmological equivalence principle is applied to the problem of synchronisation of clocks in the observed universe. Once density perturbations grow to give density contrasts of order one on scales of tens of megaparsecs, the integrated deceleration of the local background regions of voids relative to galaxies must be accounted for in the relative synchronisation of clocks of ideal observers who measure an isotropic cosmic microwave background. The relative deceleration of the background can be expected to represent a scale in which weak-field Newtonian dynamics should be modified to account for dynamical gradients in the Ricci scalar curvature of space. This acceleration scale is estimated using the best-fit nonlinear bubble model of the universe with backreaction. At redshifts z < 0.25 the scale is found to coincide with the empirical acceleration scale of modified Newtonian dynamics. At larger redshifts the scale varies in a manner which is likely to be important for understanding dynamics of galaxy clusters, and structure formation. Although the relative deceleration, typically of order 10^{-10} m/s^2, is small, when integrated over the lifetime of the universe it amounts to an accumulated relative difference of 38% in the rate of average clocks in galaxies as compared to volume-average clocks in the emptiness of voids. A number of foundational aspects of the cosmological equivalence principle are also discussed, including its relation to Mach's principle, the Weyl curvature hypothesis and the initial conditions of the universe. Journal reference: Phys.Rev.D78:084032,2008 ****************************************************************************** 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:0712.2050v3 Search of S3 LIGO data for gravitational wave signals from spinning black hole and neutron star binary inspirals Authors: The LIGO Scientific Collaboration: B. Abbott, et al (Submitted on 12 Dec 2007 (v1), last revised 30 Jun 2008 (this version, v3)) 18 pages, 8 figures We report on the methods and results of the first dedicated search for gravitational waves emitted during the inspiral of compact binaries with spinning component bodies. We analyze 788 hours of data collected during the third science run (S3) of the LIGO detectors. We searched for binary systems using a detection template family designed specially to capture the effects of the spin-induced precession of the orbital plane. We present details of the techniques developed to enable this search for spin-modulated gravitational waves, highlighting the differences between this and other recent searches for binaries with non-spinning components. The template bank we employed was found to yield high matches with our spin-modulated target waveform for binaries with masses in the asymmetric range 1.0 Msol < m1 < 3.0 Msol and 12.0 Msol < m2 < 20.0 Msol which is where we would expect the spin of the binary's components to have significant effect. We find that our search of S3 LIGO data had good sensitivity to binaries in the Milky Way and to a small fraction of binaries in M31 and M33 with masses in the range 1.0 Msol < m1, m2 < 20.0Msol. No gravitational wave signals were identified during this search. Assuming a binary population with spinning components and Gaussian distribution of masses representing a prototypical neutron star - black hole system with m1 ~ 1.35 Msol and m2 ~ 5 Msol, we calculate the 90%-confidence upper limit on the rate of coalescence of these systems to be 15.9 yr^-1 L_10^-1, where L_10 is 10^10 times the blue light luminosity of the Sun. Journal reference: Phys.Rev.D78:042002,2008 ----------------------------------------------------------------------------- arXiv:0801.3429v1 Searching for stochastic gravitational-wave background with the co-located LIGO interferometers Authors: Nickolas V Fotopoulos, for the LIGO Scientific Collaboration (Submitted on 22 Jan 2008) Proceedings paper from the 7th Edoardo Amaldi Conference on Gravitational Waves, held in Sydney, Australia from 8-14 July 2007. This paper presents techniques developed by the LIGO Scientific Collaboration to search for the stochastic gravitational-wave background using the co-located pair of LIGO interferometers at Hanford, WA. We use correlations between interferometers and environment monitoring instruments, as well as time-shifts between two interferometers (described here for the first time) to identify correlated noise from non- gravitational sources. We veto particularly noisy frequency bands and assess the level of residual non-gravitational coupling that exists in the surviving data. Journal reference: J.Phys.Conf.Ser.122:012032,2008 ----------------------------------------------------------------------------- arXiv:0802.0393v1 GRB-triggered searches for gravitational waves in LIGO data Authors: Alexander Dietz, for the LIGO Scientific Collaboration (Submitted on 4 Feb 2008) 5 pages, 3 figures, contributed talk, submitted to the proceedings of Gamma Ray Bursts 2007, Santa Fe, New Mexico, November 5-9 2007 The LIGO gravitational wave detectors have recently reached their design sensitivity and finished a two-year science run. During this period one year of data with unprecedented sensitivity has been collected. I will briefly describe the status of the LIGO detectors and the overall quality of the most recent science run. I also will present results of a search for inspiral waveforms in gravitational wave data coincident with the short gamma ray burst detected on 1st February 2007, with its sky location error box overlapping a spiral arms of M31. No gravitational wave signals were detected and a binary merger in M31 can be excluded at the 99% confidence level. ----------------------------------------------------------------------------- arXiv:0802.4320v1 Astrophysically Triggered Searches for Gravitational Waves: Status and Prospects Authors: The LIGO Scientific Collaboration, Virgo Collaboration (Submitted on 29 Feb 2008) In gravitational-wave detection, special emphasis is put onto searches that focus on cosmic events detected by other types of astrophysical observatories. The astrophysical triggers, e.g. from gamma-ray and X-ray satellites, optical telescopes and neutrino observatories, provide a trigger time for analyzing gravitational wave data coincident with the event. In certain cases the expected frequency range, source energetics, directional and progenitor information is also available. Beyond allowing the recognition of gravitational waveforms with amplitudes closer to the noise floor of the detector, these triggered searches should also lead to rich science results even before the onset of Advanced LIGO. In this paper we provide a broad review of LIGO's astrophysically triggered searches and the sources they target. Journal reference: Class.Quant.Grav.25:114051,2008 ----------------------------------------------------------------------------- arXiv:0804.1747v1 The Einstein@Home search for periodic gravitational waves in LIGO S4 data Authors: LIGO Scientific Collaboration: B. Abbott, et al (Submitted on 10 Apr 2008) 29 pages, 19 figures A search for periodic gravitational waves, from sources such as isolated rapidly-spinning neutron stars, was carried out using 510 hours of data from the fourth LIGO science run (S4). The search was for quasi- monochromatic waves in the frequency range from 50 Hz to 1500 Hz, with a linear frequency drift f-dot (measured at the solar system barycenter) in the range -f/tau < f-dot < 0.1 f/tau, where the minimum spin-down age tau was 1000 years for signals below 300 Hz and 10000 years above 300 Hz. The main computational work of the search was distributed over approximately 100000 computers volunteered by the general public. This large computing power allowed the use of a relatively long coherent integration time of 30 hours, despite the large parameter space searched. No statistically significant signals were found. The sensitivity of the search is estimated, along with the fraction of parameter space that was vetoed because of contamination by instrumental artifacts. In the 100 Hz to 200 Hz band, more than 90% of sources with dimensionless gravitational wave strain amplitude greater than 1e-23 would have been detected. ----------------------------------------------------------------------------- arXiv:0805.2412v2 Detection Confidence Tests for Burst and Inspiral Candidate Events Authors: R. Gouaty, for the LIGO Scientific Collaboration (Submitted on 15 May 2008 (v1), last revised 17 Sep 2008 (this version, v2)) 15 pages, 8 figures, Contribution to 12th Gravitational Wave Data Analysis Workshop. The LIGO Scientific Collaboration (LSC) is developing and running analysis pipelines to search for gravitational-wave transients emitted by astrophysical events such as compact binary mergers or core-collapse supernovae. However, because of the non-Gaussian, non-stationary nature of the noise exhibited by the LIGO detectors, residual false alarms might be found at the end of the pipelines. A critical aspect of the search is then to assess our confidence for gravitational waves and to distinguish them from those false alarms. Both the 'Compact Binary Coalescence' and the 'Burst' working groups have been developing a detection checklist for the validation of candidate-events, consisting of a series of tests which aim to corroborate a detection or to eliminate a false alarm. These tests include for example data quality checks, analysis of the candidate appearance, parameter consistency studies and coherent analysis. In this paper, the general methodology used for candidate validation is presented. The method is illustrated with an example of simulated gravitational-wave signal and a false alarm. Journal reference: Class.Quant.Grav.25:184006,2008 ----------------------------------------------------------------------------- arXiv:0805.4758v2 [astro-ph] Beating the spin-down limit on gravitational wave emission from the Crab pulsar Authors: The LIGO Scientific Collaboration: B. Abbott, et al (Submitted on 30 May 2008 (v1), last revised 22 Jul 2008 (this version, v2)) Accepted for Ap. J. Lett. Minor changes in results due to calibration correction We present direct upper limits on gravitational wave emission from the Crab pulsar using data from the first nine months of the fifth science run of the Laser Interferometer Gravitational-wave Observatory (LIGO). These limits are based on two searches. In the first we assume that the gravitational wave emission follows the observed radio timing, giving an upper limit on gravitational wave emission that beats indirect limits inferred from the spin-down and braking index of the pulsar and the energetics of the nebula. In the second we allow for a small mismatch between the gravitational and radio signal frequencies and interpret our results in the context of two possible gravitational wave emission mechanisms. ----------------------------------------------------------------------------- arXiv:0807.2834v2 First joint search for gravitational-wave bursts in LIGO and GEO600 data Authors: LIGO Scientific Collaboration: B. Abbott, et al (Submitted on 17 Jul 2008 (v1), last revised 15 Oct 2008 (this version, v2)) 30 pages, 8 figures We present the results of the first joint search for gravitational-wave bursts by the LIGO and GEO600 detectors. We search for bursts with characteristic central frequencies in the band 768 to 2048 Hz in the data acquired between the 22nd of February and the 23rd of March, 2005 (fourth LSC Science Run - S4). We discuss the inclusion of the GEO600 data in the Waveburst-CorrPower pipeline that first searches for coincident excess power events without taking into account differences in the antenna responses or strain sensitivities of the various detectors. We compare the performance of this pipeline to that of the coherent Waveburst pipeline based on the maximum likelihood statistic. This likelihood statistic is derived from a coherent sum of the detector data streams that takes into account the antenna patterns and sensitivities of the different detectors in the network. We find that the coherentWaveburst pipeline is sensitive to signals of amplitude 30 - 50% smaller than the Waveburst-CorrPower pipeline. We perform a search for gravitational-wave bursts using both pipelines and find no detection candidates in the S4 data set when all four instruments were operating stably. ----------------------------------------------------------------------------- arXiv:0810.0283v1 All-sky LIGO Search for Periodic Gravitational Waves in the Early S5 Data Authors: LIGO Scientific Collaboration (Submitted on 1 Oct 2008) 6 pages, 1 figure We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50--1100 Hz and with the frequency's time derivative in the range -5.0E-9 Hz/s to zero. Data from the first eight months of the fifth LIGO science run (S5) have been used in this search, which is based on a semi-coherent method (PowerFlux) of summing strain power. Observing no evidence of periodic gravitational radiation, we report 95% confidence-level upper limits on radiation emitted by any unknown isolated rotating neutron stars within the search range. Strain limits below 1.E-24 are obtained over a 200-Hz band, and the sensitivity improvement over previous searches increases the spatial volume sampled by an average factor of about 100 over the entire search band. For a neutron star with nominal equatorial ellipticity of 1.0E-6, the search is sensitive to distances as great as 500 pc - a range that could encompass many undiscovered neutron stars, albeit only a tiny fraction of which would likely be rotating fast enough to be accessible to LIGO. This ellipticity is at the upper range thought to be sustainable by conventional neutron stars and well below the maximum sustainable by a strange quark star. -----------------------------------------------------------------------------