Subject: ASGRG Newsletter #15 ****************************************************************************** AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION Electronic Newsletter -- #15, 2005 ****************************************************************************** Items for this newsletter should be emailed to the editor: asgrg *AT* hotmail *DOT* com The deadline for the next issue is 31 October, 2006. ****************************************************************************** CONTENTS: * POSTPONEMENT OF 5TH AUSTRALASIAN CONFERENCE ON GENERAL RELATIVITY AND GRAVITATION (ACGRG5) * REPLACEMENT OF ASGRG TREASURER * MEMBERSHIP DETAILS ONLINE at http://www.physics.adelaide.edu.au/ASGRG/members.html * SUBSCRIPTIONS * FORTHCOMING MEETINGS * MEMBERS' ABSTRACTS at gr-qc, December 2004 - November 2005 * ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc, December 2004 - November 2005 ****************************************************************************** Fifth Australasian Conference on General Relativity & Gravitation -------------------------------------------------------------------------- ACGRG5 POSTPONED The Fifth Australasian Conference was originally to have been held in Christchurch in 2006. However, we are unfortunately unable to find a mutually convenient date in which to run the meeting, the suggestion of January being impossible for the local organiser because of other commitments on one hand, and clashes between New Zealand and Australian semester breaks at other times in the year on the other. Since there are two major international conferences in our region soon- the Texas meeting in Melbourne in December 2006 and GR18 in Sydney 2007 - it does not seem practical to be running another meeting in 2006 and so the ASGRG committee propose that we postpone the 2006 BGM until the time of GR18 in Sydney when a majority of members will be present. The venue for the next ACGRG will be decided then. ****************************************************************************** REPLACEMENT OF ASGRG TREASURER Antony Searle resigned from his position as ASGRG Treasurer on 22 November 2005. We would like to thank Antony for all his efforts on behalf of the Society over the years. The Executive Committee decided unanimously to elect John Steele as the new ASGRG Treasurer to fill the casual vacancy caused by Antony's departure. ****************************************************************************** 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 2006 - June 2007 subscriptions are requested, if you wish to pay for July 2007 - June 2008 at the same time, it may simplify matters. ****************************************************************************** FORTHCOMING MEETINGS March 2-6, 2006: International Conference on Gravitation, Cosmology and Astrophysics Moscow, Russia http://www.rgs.da.ru/ July 23-29, 2006: 11th Marcel Grossman Meeting on General Relativity (MG11) Freie Univesitaet, Berlin http://www.icra.it/MG/mg11/ December 11-15, 2006: Texas in Australia: 23rd Texas Symposium on Relativistic Astrophysics University of Melbourne, Melbourne, Australia July 8-13, 2007: 18th International Conference on General Relativity and Gravitation (GR18) Darling Harbour, Sydney, Australia ****************************************************************************** MEMBERS' ABSTRACTS at gr-qc, December 2004 - November 2005 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. ----------------------------------------------------------------------------- gr-qc/0505160 From: Malcolm Anderson Date: Tue, 31 May 2005 15:04:17 GMT (231kb) Self-Similar Evaporation of a Rigidly-Rotating Cosmic String Loop Authors: Malcolm Anderson Comments: 41 pages, 5 figures. Accepted for publication in Classical and Quantum Gravity Journal-ref: Class.Quant.Grav. 22 (2005) 2539-2568 The gravitational back-reaction on a certain type of rigidly-rotating cosmic string loop, first discovered by Allen, Casper and Ottewill, is studied at the level of the weak-field approximation. The near-field metric perturbations are calculated and used to construct the self- acceleration vector of the loop. Although the acceleration vector is divergent at the two kink points on the loop, its net effect on the trajectory over a single oscillation period turns out to be finite. The net back-reaction on the loop over a single period is calculated using a method due to Quashnock and Spergel, and is shown to induce a uniform shrinkage of the loop while preserving its original shape. The loop therefore evolves by self-similar evaporation. ----------------------------------------------------------------------------- gr-qc/0505103 From: Dr. Bikash Chandra Paul Date: Fri, 20 May 2005 07:40:14 GMT (16kb) Emergent Universe in Starobinsky Model Authors: S. Mukherjee, B. C. Paul, S. D. Maharaj, A. Beesham Comments: 12 pages, 3 figures We present an emergent universe scenario making use of a new solution of the Starobinsky model. The solution belongs to a one parameter family of solutions, where the parameter is determined by the number and the species (spin-values) of primordial fields. The general features of the model have also been studied. ----------------------------------------------------------------------------- gr-qc/0502079 From: Chunnong Zhao Date: Fri, 18 Feb 2005 02:46:01 GMT (209kb) Parametric instabilities and their control in advanced interferometer GW detectors Authors: C. Zhao, L. Ju, J. Degallaix, S. Gras, D. G. Blair Comments: 5 pages, 4 figures Journal-ref: Phys.Rev.Lett. 94 (2005) 121102 A detailed simulation of Advanced LIGO test mass optical cavities shows that parametric instabilities will excite acoustic modes in the test masses in the frequency range 28-35 kHz and 64-72 kHz. Using nominal Advanced LIGO optical cavity parameters with fused silica test masses, parametric instability excites 7 acoustic modes in each test mass, with parametric gain R up to 7. For the alternative sapphire test masses only 1 acoustic mode is excited in each test mass with R ~ 2. Fine tuning of the test mass radii of curvature cause the instabilities to sweep through various modes with R as high as ~2000. Sapphire test mass cavities can be tuned to completely eliminate instabilities using thermal g-factor tuning with negligible degradation of the noise performance. In the case of fused silica test mass, instabilities can be minimized but not eliminated. ----------------------------------------------------------------------------- gr-qc/0507006 From: Brandon Carter Date: Sun, 3 Jul 2005 13:50:51 GMT (35kb) Covariant Newtonian and Relativistic dynamics of (magneto)-elastic solid model for neutron star crust Authors: Brandon Carter, Elie Chachoua, Nicolas Chamel Comments: 39 pages Latex This work develops the dynamics of perfectly elastic solid model for application to the outer crust of a magnetised neutron star. Particular attention is given to the Noether identities responsible for energy-momentum conservation, using a formulation that is fully covariant, not only (as is usual) in a fully relativistic treatment but also (sacrificing accuracy and elegance for economy of degrees of gravitational freedom) in the technically more complicated case of the Newtonian limit. The results are used to obtain explicit (relativistic and Newtonian) formulae for the propagation speeds of generalised (Alfven type) magneto-elastic perturbation modes. ----------------------------------------------------------------------------- gr-qc/0504012 From: Edward Porter Date: Mon, 4 Apr 2005 18:41:16 GMT (24kb) Detecting Galactic Binaries with LISA Authors: Neil J. Cornish, Edward K. Porter Comments: 6 pages-1 figure, Proceedings of GWDAW 9, Submitted to Classical and Quantum Gravity One of the main sources of gravitational waves for the LISA space-borne interferometer are galactic binary systems. The waveforms for these sources are represented by eight parameters, of which four are extrinsic, and four are intrinsic to the system. Geometrically, these signals exist in an 8-d parameter space. By calculating the metric tensor on this space, we calculate the number of templates needed to search for such sources. We show in this study that below a particular monochromatic frequency, we can ignore one of the intrinsic parameters and search over a 7-d space. Beyond this frequency, we have a sudden change in dimensionality of the parameter space from 7 to 8 dimensions, which results in a change in the scaling of the growth of template number as a function of monochromatic frequency. ----------------------------------------------------------------------------- gr-qc/0504071 From: Neil J. Cornish Date (v1): Fri, 15 Apr 2005 19:30:41 GMT (283kb) Date (revised v2): Sat, 16 Apr 2005 19:01:28 GMT (179kb) Characterizing the Galactic Gravitational Wave Background with LISA Authors: Seth E. Timpano, Louis J. Rubbo, Neil J. Cornish Comments: 29 pages, 12 figures We present a Monte Carlo simulation for the response of the Laser Interferometer Space Antenna (LISA) to the galactic gravitational wave background. The simulated data streams are used to estimate the number and type of binary systems that will be individually resolved. We find that the background is highly non-Gaussian due to the presence of individual bright sources, but once these sources are identified and removed, the remaining signal is Gaussian. We give a new estimate of the confusion noise due to the unresolved sources that differs significantly from earlier estimates. ----------------------------------------------------------------------------- gr-qc/0506015 From: Neil J. Cornish Date (v1): Fri, 3 Jun 2005 16:46:52 GMT (46kb) Date (revised v2): Fri, 17 Jun 2005 04:35:37 GMT (46kb) Date (revised v3): Mon, 17 Oct 2005 19:04:42 GMT (54kb) Beyond LISA: Exploring Future Gravitational Wave Missions Authors: Jeff Crowder, Neil J. Cornish Comments: 9 pages, 10 figures, published version Journal-ref: Phys.Rev. D72 (2005) 083005 The Advanced Laser Interferometer Antenna (ALIA) and the Big Bang Observer (BBO) have been proposed as follow on missions to the Laser Interferometer Space Antenna (LISA). Here we study the capabilities of these observatories, and how they relate to the science goals of the missions. We find that the Advanced Laser Interferometer Antenna in Stereo (ALIAS), our proposed extension to the ALIA mission, will go considerably further toward meeting ALIA's main scientific goal of studying intermediate mass black holes. We also compare the capabilities of LISA to a related extension of the LISA mission, the Laser Interferometer Space Antenna in Stereo (LISAS). Additionally, we find that the initial deployment phase of the BBO would be sufficient to address the BBO's key scientific goal of detecting the Gravitational Wave Background, while still providing detailed information about foreground sources. ----------------------------------------------------------------------------- gr-qc/0506059 From: Neil J. Cornish Date: Fri, 10 Jun 2005 19:51:28 GMT (196kb) LISA Data Analysis using MCMC methods Authors: Neil J. Cornish, Jeff Crowder Comments: 14 pages, 7 figures Journal-ref: Phys.Rev. D72 (2005) 043005 The Laser Interferometer Space Antenna (LISA) is expected to simultaneously detect many thousands of low frequency gravitational wave signals. This presents a data analysis challenge that is very different to the one encountered in ground based gravitational wave astronomy. LISA data analysis requires the identification of individual signals from a data stream containing an unknown number of overlapping signals. Because of the signal overlaps, a global fit to all the signals has to be performed in order to avoid biasing the solution. However, performing such a global fit requires the exploration of an enormous parameter space with a dimension upwards of 50,000. Markov Chain Monte Carlo (MCMC) methods offer a very promising solution to the LISA data analysis problem. MCMC algorithms are able to efficiently explore large parameter spaces, simultaneously providing parameter estimates, error analyses and even model selection. Here we present the first application of MCMC methods to simulated LISA data and demonstrate the great potential of the MCMC approach. Our implementation uses a generalized F-statistic to evaluate the likelihoods, and simulated annealing to speed convergence of the Markov chains. As a final step we super-cool the chains to extract maximum likelihood estimates, and estimates of the Bayes factors for competing models. We find that the MCMC approach is able to correctly identify the number of signals present, extract the source parameters, and return error estimates consistent with Fisher information matrix predictions. ----------------------------------------------------------------------------- cond-mat/0501182 From: Craig M. Savage Date: Mon, 10 Jan 2005 02:36:02 GMT (53kb) Superradiant scattering from a hydrodynamic vortex Authors: T.R. Slatyer, C.M. Savage Comments: 10 pages, 1 figure We show that sound waves scattered from a hydrodynamic vortex may be amplified. Such superradiant scattering follows from the physical analogy between spinning black holes and hydrodynamic vortices. However a sonic horizon analogous to the black hole event horizon does not exist unless the vortex possesses a central drain, which is challenging to produce experimentally. In the astrophysical domain, superradiance can occur even in the absence of an event horizon: we show that in the hydrodynamic analogue, a drain is not required and a vortex scatters sound superradiantly. Possible experimental realization in dilute gas Bose- Einstein condensates is discussed. ----------------------------------------------------------------------------- gr-qc/0508098 From: Andrew Moylan Date: Wed, 24 Aug 2005 03:26:07 GMT (119kb) Developments in GRworkbench Authors: A. Moylan, S.M. Scott, A.C. Searle Comments: 14 pages. To appear A. Moylan, S.M. Scott and A.C. Searle, Developments in GRworkbench. Proceedings of the Tenth Marcel Grossmann Meeting on General Relativity, editors M. Novello, S. Perez-Bergliaffa and R. Ruffini. Singapore: World Scientific 2005 The software tool GRworkbench is an ongoing project in visual, numerical General Relativity at The Australian National University. Recently, GRworkbench has been significantly extended to facilitate numerical experimentation in analytically-defined space-times. The numerical differential geometric engine has been rewritten using functional programming techniques, enabling objects which are normally defined as functions in the formalism of differential geometry and General Relativity to be directly represented as function variables in the C++ code of GRworkbench. The new functional differential geometric engine allows for more accurate and efficient visualisation of objects in space-times and makes new, efficient computational techniques available. Motivated by the desire to investigate a recent scientific claim using GRworkbench, new tools for numerical experimentation have been implemented, allowing for the simulation of complex physical situations. ----------------------------------------------------------------------------- gr-qc/0412065 From: Francisco Lobo Date: Tue, 14 Dec 2004 18:13:24 GMT (26kb) Linearized warp drive and the energy conditions Authors: Francisco S. N. Lobo, Matt Visser Comments: 6 pages, contribution to the proceedings of the Spanish Relativity Meeting-2004 (Miraflores de la Sierra, Madrid, September 2004) "Warp drive" spacetimes are useful as "gedanken-experiments" and as a theoretician's probe of the foundations of general relativity. Applying linearized gravity to the weak-field warp drive, i.e., for non-relativistic warp-bubble velocities, we find that the occurrence of energy condition violations in this class of spacetimes is generic to the form of the geometry under consideration and is not simply a side-effect of the "superluminal" properties. Using the linearized construction it is now possible to compare the warp field energy with the mass-energy of the spaceship, and applying the "volume integral quantifier", extremely stringent conditions on the warp drive spacetime are found. ----------------------------------------------------------------------------- gr-qc/0503007 From: Matt Visser Date: Wed, 2 Mar 2005 03:25:03 GMT (54kb) Generating perfect fluid spheres in general relativity Authors: Petarpa Boonserm, Matt Visser, Silke Weinfurtner Comments: 18 pages, 4 tables, 4 figures Ever since Karl Schwarzschild's 1916 discovery of the spacetime geometry describing the interior of a particular idealized general relativistic star -- a static spherically symmetric blob of fluid with position-independent density -- the general relativity community has continued to devote considerable time and energy to understanding the general-relativistic static perfect fluid sphere. Over the last 90 years a tangle of specific perfect fluid spheres has been discovered, with most of these specific examples seemingly independent from each other. To bring some order to this collection, in this article we develop several new transformation theorems that map perfect fluid spheres into perfect fluid spheres. These transformation theorems sometimes lead to unexpected connections between previously known perfect fluid spheres, sometimes lead to new previously unknown perfect fluid spheres, and in general can be used to develop a systematic way of classifying the set of all perfect fluid spheres. ----------------------------------------------------------------------------- gr-qc/0505065 From: Matt Visser Date (v1): Fri, 13 May 2005 03:50:40 GMT (281kb) Date (revised v2): Wed, 1 Jun 2005 00:16:05 GMT (362kb) Analogue Gravity Authors: Carlos Barcelo (IAA, Granada), Stefano Liberati (SISSA/ISAS, Trieste), Matt Visser (Victoria University of Wellington) Comments: V1: 151 pages; 12 figures; 427 references. This is a draft of a "Living Review" that will shortly be submitted to the Journal "Living Reviews in General Relativity". Constructive comments are welcome. V2: 152 pages, added 8 references and expanded discussion of a few technical points Analogue models of (and for) gravity have a long and distinguished history dating back to the earliest years of general relativity. In this review article we will discuss the history, aims, results, and future prospects for the various analogue models. We start the discussion by presenting a particularly simple example of an analogue model, before exploring the rich history and complex tapestry of models discussed in the literature. The last decade in particular has seen a remarkable and sustained development of analogue gravity ideas, leading to some hundreds of published articles, a workshop, two books, and this review article. Future prospects for the analogue gravity programme also look promising, both on the experimental front (where technology is rapidly advancing) and on the theoretical front (where variants of analogue models can be used as a springboard for radical attacks on the problem of quantum gravity). ----------------------------------------------------------------------------- gr-qc/0505137 From: Matt Visser Date: Fri, 27 May 2005 02:36:51 GMT (21kb) Gravastars must have anisotropic pressures Authors: Celine Cattoen (Victoria University of Wellington), Tristan Faber (Victoria University of Wellington), Matt Visser (Victoria University of Wellington) Comments: 15 pages; 4 figures; uses iopart.cls One of the very small number of serious alternatives to the usual concept of an astrophysical black hole is the "gravastar" model developed by Mazur and Mottola; and a related phase-transition model due to Laughlin et al. We consider a generalized class of similar models that exhibit continuous pressure -- without the presence of infinitesimally thin shells. By considering the usual TOV equation for static solutions with negative central pressure, we find that gravastars cannot be perfect fluids -- anisotropic pressures in the "crust" of a gravastar-like object are unavoidable. The anisotropic TOV equation can then be used to bound the pressure anisotropy. The transverse stresses that support a gravastar permit a higher compactness than is given by the Buchdahl--Bondi bound for perfect fluid stars. Finally we comment on the qualitative features of the equation of state that gravastar material must have if it is to do the desired job of preventing horizon formation. ----------------------------------------------------------------------------- gr-qc/0506029 From: Matt Visser Date (v1): Mon, 6 Jun 2005 07:28:13 GMT (18kb) Date (revised v2): Wed, 8 Jun 2005 08:48:39 GMT (18kb) Massive Klein--Gordon equation from a BEC-based analogue spacetime Authors: Matt Visser (Victoria University of Wellington), Silke Weinfurtner (Victoria University of Wellington) Comments: V1: 10 pages; uses revtex4; V2: two references and brief comments added Journal-ref: Phys.Rev. D72 (2005) 044020 We extend the "analogue spacetime" programme by investigating a condensed- matter system that is in principle capable of simulating the massive Klein -Gordon equation in curved spacetime. Since many elementary particles have mass, this is an essential step in building realistic analogue models, and a first step towards simulating quantum gravity phenomenology. Specifically, we consider the class of two-component BECs subject to laser-induced transitions between the components. This system exhibits a complicated spectrum of normal mode excitations, which can be viewed as two interacting phonon modes that exhibit the phenomenon of "refringence". We study the conditions required to make these two phonon modes decouple. Once decoupled, the two distinct phonons generically couple to distinct effective spacetimes, representing a bi-metric model, with one of the modes acquiring a mass. In the eikonal limit the massive mode exhibits the dispersion relation of a massive relativistic particle: omega = sqrt[omega_0^2 + c^2 k^2], plus curved-space modifications. Furthermore, it is possible to tune the system so that both modes can be arranged to travel at the same speed, in which case the two phonon excitations couple to the same effective metric. From the analogue spacetime perspective this situation corresponds to the Einstein equivalence principle being satisfied. ----------------------------------------------------------------------------- gr-qc/0508045 From: Matt Visser Date (v1): Thu, 11 Aug 2005 04:49:42 GMT (16kb) Date (revised v2): Tue, 30 Aug 2005 04:11:11 GMT (16kb) Necessary and sufficient conditions for big bangs, bounces, crunches, rips, sudden singularities, and extremality events Authors: Celine Cattoen (Victoria University of Wellington), Matt Visser (Victoria University of Wellington) Comments: 20 pages, uses iopart.cls; several references added Journal-ref: Class.Quant.Grav. 22 (2005) 4913-4930 The physically relevant singularities occurring in FRW cosmologies had traditionally been thought to be limited to the "big bang", and possibly a "big crunch". However, over the last few years, the zoo of cosmological singularities considered in the literature has become considerably more extensive, with "big rips" and "sudden singularities" added to the mix, as well as renewed interest in non-singular cosmological events such as "bounces" and "turnarounds". In this article we present a complete catalogue of such cosmological milestones, both at the kinematical and dynamical level. First, using generalized power series, purely kinematical definitions of these cosmological events are provided in terms of the behaviour of the scale factor a(t). The notion of a "scale-factor singularity'" is defined, and its relation to curvature singularities (polynomial and differential) is explored. Second, dynamical information is extracted by using the Friedmann equations (without assuming even the existence of any equation of state) to place constraints on whether or not the classical energy conditions are satisfied at the cosmological milestones. We use these considerations to derive necessary and sufficient conditions for the existence of cosmological milestones such as bangs, bounces, crunches, rips, sudden singularities, and extremality events. Since the classification is extremely general, the corresponding results are to a high degree model-independent: In particular, we provide a complete characterization of the class of bangs, crunches, and sudden singularities for which the dominant energy condition is satisfied. ----------------------------------------------------------------------------- gr-qc/0510083 From: Matt Visser Date (v1): Tue, 18 Oct 2005 03:10:58 GMT (20kb) Date (revised v2): Wed, 26 Oct 2005 08:58:10 GMT (21kb) Production and decay of evolving horizons Authors: Matt Visser (Victoria University of Wellington), Alex B. Nielsen (University of Canterbury) Comments: 23 pages, uses iopart.cls V2: 5 references added; minor typos We consider a simple physical model for an evolving horizon that is strongly interacting with its environment, exchanging arbitrarily large quantities of matter with its environment in the form of both infalling material and outgoing Hawking radiation. We permit fluxes of both lightlike and timelike particles to cross the horizon, and ask how the horizon grows and shrinks in response to such flows. We place a premium on providing a clear and straightforward exposition with simple formulae. To be able to handle such a highly dynamical situation in a simple manner we make one significant physical restriction, that of spherical symmetry, and two technical mathematical restrictions: (1) We choose to slice the spacetime in such a way that the space-time foliations (and hence the horizons) are always spherically symmetric. (2) Furthermore we adopt Painleve-Gullstrand coordinates (which are well suited to the problem because they are nonsingular at the horizon) in order to simplify the relevant calculations. We find particularly simple forms for surface gravity, and for the first and second law of black hole thermodynamics, in this general evolving horizon situation. Furthermore we relate our results to Hawking's apparent horizon, Ashtekar's isolated and dynamical horizons, and Hayward's trapping horizons. The evolving black hole model discussed here will be of interest, both from an astrophysical viewpoint in terms of discussing growing black holes, and from a purely theoretical viewpoint in discussing black hole evaporation via Hawking radiation. ----------------------------------------------------------------------------- gr-qc/0510125 From: Matt Visser Date: Sun, 30 Oct 2005 06:28:37 GMT (34kb) Analogue quantum gravity phenomenology from a two-component Bose-Einstein condensate Authors: Stefano Liberati (Sissa, Trieste and INFN, Italy), Matt Visser (Victoria University of Wellington), Silke Weinfurtner (Victoria University of Wellington) Comments: 36 pages, uses iopart.sty We present an analogue spacetime model that reproduces the salient features of the most common ansatz for quantum gravity phenomenology. We do this by investigating a system of two coupled Bose-Einstein condensates. This system can be tuned to have two "phonon" modes (one massive, one massless) which share the same limiting speed in the hydrodynamic approximation [Phys. Rev. D72 (2005) 044020, gr-qc/0506029; cond-mat/0409639]. The system nevertheless possesses (possibly non-universal) Lorentz violating terms at very high energies where "quantum pressure" becomes important. We investigate the physical interpretation of the relevant fine-tuning conditions, and discuss the possible lessons and hints that this analogue spacetime could provide for the phenomenology of real physical quantum gravity. In particular we show that the effective field theory of quasi- particles in such an emergent spacetime does not exhibit the so called "naturalness problem". ----------------------------------------------------------------------------- gr-qc/0511105 From: Silke Weinfurtner Date: Fri, 18 Nov 2005 03:24:52 GMT (11kb) Analogue model for quantum gravity phenomenology Authors: Silke Weinfurtner, Stefano Liberati, Matt Visser Comments: Talk given at 7th Workshop on Quantum Field Theory Under the Influence of External Conditions (QFEXT 05), Barcelona, Catalonia, Spain, 5-9 Sep 2005 So called "analogue models" use condensed matter systems (typically hydrodynamic) to set up an "effective metric" and to model curved-space quantum field theory in a physical system where all the microscopic degrees of freedom are well understood. Known analogue models typically lead to massless minimally coupled scalar fields. We present an extended "analogue space-time" programme by investigating a condensed-matter system - in and beyond the hydrodynamic limit - that is in principle capable of simulating the massive Klein-Gordon equation in curved spacetime. Since many elementary particles have mass, this is an essential step in building realistic analogue models, and an essential first step towards simulating quantum gravity phenomenology. Specifically, we consider the class of two-component BECs subject to laser-induced transitions between the components, and we show that this model is an example for Lorentz invariance violation due to ultraviolet physics. Furthermore our model suggests constraints on quantum gravity phenomenology in terms of the "naturalness problem" and "universality issue". ----------------------------------------------------------------------------- hep-th/0502003 From: David Wiltshire Date (v1): Tue, 1 Feb 2005 20:55:24 GMT (13kb) Date (revised v2): Thu, 10 Feb 2005 20:45:52 GMT (14kb) *Date (revised v3): Fri, 1 Jul 2005 13:25:34 GMT (14kb) Accelerating cosmologies from compactification with a twist Authors: Ishwaree P. Neupane, David L. Wiltshire Comments: 5 pages, 1 figure, RevTeX4 Journal-ref: Phys.Lett. B619 (2005) 201 DOI: 10.1016/j.physletb.2005.06.008 It is demonstrated by explicit solutions of the (4+n)-dimensional vacuum Einstein equations that accelerating cosmologies in the Einstein conformal frame can be obtained by a time-dependent compactification of string/M-theory, even in the case that internal dimensions are Ricci-flat, provided one includes one or more geometric twists. Such acceleration is transient. When both compact hyperbolic internal spaces and geometric twists are included, however, the period of accelerated expansion may be made arbitrarily large. ----------------------------------------------------------------------------- gr-qc/0503099 From: David Wiltshire [view email] Date (v1): Wed, 23 Mar 2005 10:22:03 GMT (14kb) Date (revised v2): Thu, 24 Mar 2005 17:45:02 GMT (14kb) Date (revised v3): Fri, 25 Mar 2005 04:13:08 GMT (15kb) Date (revised v4): Wed, 6 Apr 2005 20:00:16 GMT (17kb) Date (revised v5): Mon, 11 Jul 2005 11:22:10 GMT (19kb) Viable inhomogeneous model universe without dark energy from primordial inflation Authors: David L. Wiltshire Comments: 4 pages, aastex, emualteapj5.sty. v5: Complete overhaul of notation and presentation to improve clarity. Corrected volume factor increases age of universe A new model of the observed universe, using solutions to the full Einstein equations, is developed from the hypothesis that our observable universe is an underdense bubble, with an internally inhomogeneous fractal bubble distribution of bound matter systems, in a spatially flat bulk universe. It is argued on the basis of primordial inflation and resulting structure formation, that the clocks of the isotropic observers in average galaxies coincide with clocks defined by the true surfaces of matter homogeneity of the bulk universe, rather than the comoving clocks at average spatial positions in the underdense bubble geometry, which are in voids. This understanding requires a systematic reanalysis of all observed quantities in cosmology. I begin such a reanalysis by giving a model of the average geometry of the universe, which depends on two measured parameters: the present matter density parameter, Omega_m, and the Hubble constant, H_0. The observable universe is not accelerating. Nonetheless, inferred luminosity distances are larger than naively expected, in accord with the evidence of distant type Ia supernovae. The predicted age of the universe is 15.3 +/-0.7 Gyr. The expansion age is larger than in competing models, and may account for observed structure formation at large redshifts. ----------------------------------------------------------------------------- astro-ph/0504192 From: David Wiltshire Date (v1): Fri, 8 Apr 2005 10:57:51 GMT (68kb) Date (revised v2): Tue, 12 Apr 2005 10:12:13 GMT (73kb) Date (revised v3): Mon, 11 Jul 2005 11:35:25 GMT (71kb) Type Ia supernovae tests of fractal bubble universe with no cosmic acceleration Authors: B.M.N. Carter, B.M. Leith, S.C.C. Ng, A.B. Nielsen, D.L. Wiltshire Comments: 10 pages, 5 figures, aastex. v3: Corrected volume factor changes parameter estimates and discussion, figures redrawn, references added The unexpected dimness of Type Ia supernovae at redshifts z >~ 1 has over the past 7 years been seen as an indication that the expansion of the universe is accelerating. A new model cosmology, the "fractal bubble model", has been proposed by one of us [gr-qc/0503099], based on the idea that our observed universe resides in an underdense bubble remnant from a primordial epoch of cosmic inflation, together with a new solution for averaging in an inhomogeneous universe. Although there is no cosmic acceleration, it is claimed that the luminosity distance of type Ia supernovae data will nonetheless fit the new model, since it mimics a Milne universe at low redshifts. In this paper the hypothesis is tested statistically against the available type Ia supernovae data by both chi-square and Bayesian methods. While the standard model with cosmological constant Omega_Lambda = 1-Omega_m is favoured by a Bayesian analysis with wide priors, the comparison depends strongly on the priors chosen for the density parameter, Omega_m. The fractal bubble model gives better agreement generally for Omega_m<0.2. It also gives reasonably good fits for all the range, Omega_m=0.01-0.55, allowing the possibility of a viable cosmology with just baryonic matter, or alternatively with both baryonic matter and additional cold dark matter. ----------------------------------------------------------------------------- hep-th/0504135 From: Ishwaree P. Neupane Date (v1): Mon, 18 Apr 2005 19:46:35 GMT (92kb) Date (revised v2): Wed, 27 Apr 2005 19:49:15 GMT (93kb) Cosmic Acceleration from M Theory on Twisted Spaces Authors: Ishwaree P. Neupane, David L. Wiltshire Comments: 16 pages, 2 figures, RevTex4; references added In a recent paper [hep-th/0502003] we have found a new class of accelerating cosmologies arising from time-dependent compactifications of classical supergravities on product spaces that include one or more geometric twists along with non-trivial curved internal spaces. With such effects, a scalar potential can have a locally stable minimum with positive vacuum energy. The existence of such a minimum generically predicts a period of accelerated expansion in the four-dimensional conformal frame. Here we considerably extend our knowledge of these solutions by presenting more new examples, and discuss their properties in a more general setting, which relates the solutions to other types of solutions with simple product spaces for internal manifolds. ****************************************************************************** ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc, December 2004 - November 2005 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. ----------------------------------------------------------------------------- gr-qc/0412022 From: John T. Whelan Date: Sat, 4 Dec 2004 22:12:56 GMT (16kb) First upper limit analysis and results from LIGO science data: stochastic background Authors: John T. Whelan, for the LIGO Scientific Collaboration Comments: 7 pages; 1 eps figures; proceeding from 2003 Edoardo Amaldi Meeting on Gravitational Waves Journal-ref: Class.Quant.Grav. 21 (2004) 685-690 I describe analysis of correlations in the outputs of the three LIGO interferometers from LIGO's first science run, held over 17 days in August and September of 2002, and the resulting upper limit set on a stochastic background of gravitational waves. By searching for cross-correlations between the LIGO detectors in Livingston, LA and Hanford, WA, we are able to set a 90% confidence level upper limit of h_{100}^2 Omega_0 < 23 +/- 4.6. ----------------------------------------------------------------------------- gr-qc/0501068 From: Szabolcs M\'arka Date (v1): Mon, 24 Jan 2005 03:25:30 GMT (357kb) Date (revised v2): Sun, 20 Feb 2005 21:22:15 GMT (357kb) A Search for Gravitational Waves Associated with the Gamma Ray Burst GRB030329 Using the LIGO Detectors Authors: The LIGO Scientific Collaboration Comments: 18 pages, 9 figures and 3 tables; Minor Updates: Authorlist, Acknowledgement; Added: Ref [65] Report-no: LIGO-P040007-07-D We have performed a search for bursts of gravitational waves associated with the very bright Gamma Ray Burst GRB030329, using the two detectors at the LIGO Hanford Observatory. Our search covered the most sensitive frequency range of the LIGO detectors (approximately 80-2048 Hz), and we specifically targeted signals shorter than 150 ms. Our search algorithm looks for excess correlated power between the two interferometers and thus makes minimal assumptions about the gravitational waveform. We observed no candidates with gravitational wave signal strength larger than a pre-determined threshold. We report frequency dependent upper limits on the strength of the gravitational waves associated with GRB030329. Near the most sensitive frequency region, around 250 Hz, our root-sum-square (RSS) gravitational wave strain sensitivity for optimally polarized bursts was better than h_RSS = 6E-21 Hz^{-1/2}. Our result is comparable to the best published results searching for association between gravitational waves and GRBs. ----------------------------------------------------------------------------- gr-qc/0504065 From: Eirini Messaritaki Date: Thu, 14 Apr 2005 19:07:56 GMT (886kb) Report on the first binary black hole inspiral search in LIGO data Authors: Eirini Messaritaki, for the LIGO Scientific Collaboration Comments: 10 pages, 2 figures, submitted to CQG for inclusion in the GWDAW9 proceedings The LIGO Scientific Collaboration is currently engaged in the first search for binary black hole inspiral signals in real data. We are using the data from the second LIGO science run and we focus on inspiral signals coming from binary systems with component masses between 3 and 20 solar masses. We describe the analysis methods used and report on preliminary estimates for the sensitivities of the LIGO instruments during the second science run. ----------------------------------------------------------------------------- gr-qc/0504067 From: Nelson Christensen Date: Fri, 15 Apr 2005 11:28:16 GMT (298kb) Veto Studies for LIGO Inspiral Triggers Authors: Nelson Christensen (for the LIGO Scientific Collaboration) Comments: Submitted to Classical and Quantum Gravity for the special issue for presentations at GWDAW 9 LIGO recently conducted its third scientific data run, S3. Here we summarize the veto and data quality studies conducted by the LIGO Scientific Collaboration in connection with the search for binary inspiral signals in the S3 data. LIGO's interferometer channels and physical environmental monitors were monitored, and events in these channels coincident with inspiral triggers were examined. ----------------------------------------------------------------------------- gr-qc/0504106 From: Alessandra Di Credico Date: Thu, 21 Apr 2005 16:39:21 GMT (243kb) Gravitational wave burst vetoes in the LIGO S2 and S3 data analyses Authors: Alessandra Di Credico (for the LIGO Scientific Collaboration) Comments: 9 pages, 4 figures, submitted to Classical and Quantum Gravity for the special issue of the GWDAW9 Proceedings The LIGO detectors collected about 4 months of data in 2003-2004 during two science runs, S2 and S3. Several environmental and auxiliary channels that monitor the instruments' physical environment and overall interferometric operation were analyzed in order to establish the quality of the data as well as the presence of transients of non-astrophysical origin. This analysis allowed better understanding of the noise character of the instruments and the establishment of correlations between transients in these channels and the one recording the gravitational wave strain. In this way vetoes for spurious burst were identified. We present the methodology we followed in this analysis and the results from the S2 and S3 veto analysis within the context of the search for gravitational wave bursts. ----------------------------------------------------------------------------- gr-qc/0504128 From: Hirotaka Takahashi Date: Tue, 26 Apr 2005 01:28:38 GMT (111kb) Status of the joint LIGO--TAMA300 inspiral analysis Authors: Stephen Fairhurst, for the LIGO Scientific Collaboration, Hirotaka Takahashi, for the TAMA Collaboration Comments: 10 page, 8 figures, submitted to Classical and Quantum Gravity for the special issue of the GWDAW9 Proceedings Report-no: OU-TAP 257 We present the status of the joint search for gravitational waves from inspiraling neutron star binaries in the LIGO Science Run 2 and TAMA300 Data Taking Run 8 data, which was taken from February 14 to April 14, 2003, by the LIGO and TAMA collaborations. In this paper we discuss what has been learned from an analysis of a subset of the data sample reserved as a "playground". We determine the coincidence conditions for parameters such as the coalescence time and chirp mass by injecting simulated Galactic binary neutron star signals into the data stream. We select coincidence conditions so as to maximize our efficiency of detecting simulated signals. We obtain an efficiency for our coincident search of 78 %, and show that we are missing primarily very distant signals for TAMA300. We perform a time slide analysis to estimate the background due to accidental coincidence of noise triggers. We find that the background triggers have a very different character from the triggers of simulated signals. ----------------------------------------------------------------------------- gr-qc/0505029 From: E Katsavounidis Date: Fri, 6 May 2005 18:08:54 GMT (158kb) Upper limits on gravitational wave bursts in LIGO's second science run Authors: LIGO Scientific Collaboration Comments: 23 pages, 14 figures, to be submitted to Phys Rev D Report-no: LIGO Laboratory document P-040040-07-R We perform a search for gravitational wave bursts using data from the second science run of the LIGO detectors, using a method based on a wavelet time- frequency decomposition. This search is sensitive to bursts of duration much less than a second and with frequency content in the 100-1100Hz range. It features significant improvements in the instrument sensitivity and in the analysis pipeline with respect to the burst search previously reported by LIGO. Improvements in the search method allow exploring weaker signals, relative to the detector noise floor, while maintaining a low false alarm rate, O(0.1) microHz. The sensitivity in terms of the root-sum-square (rss) strain amplitude lies in the range of hrss~10^{-20} - 10^{-19}/sqrt(Hz) No gravitational wave signals were detected in 9.98 days of analyzed data. We interpret the search result in terms of a frequentist upper limit on the rate of detectable gravitational wave bursts at the level of 0.26 events per day at 90% confidence level. We combine this limit with measurements of the detection efficiency for given waveform morphologies in order to yield rate versus strength exclusion curves as well as to establish order-of-magnitude distance sensitivity to certain modeled astrophysical sources. Both the rate upper limit and its applicability to signal strengths improve our previously reported limits and reflect the most sensitive broad-band search for untriggered and unmodeled gravitational wave bursts to date. ----------------------------------------------------------------------------- gr-qc/0505041 From: Gabriela Gonz\'alez Date (v1): Tue, 10 May 2005 02:36:47 GMT (439kb) Date (revised v2): Thu, 12 May 2005 19:13:54 GMT (439kb) Search for gravitational waves from galactic and extra--galactic binary neutron stars Authors: LIGO Scientific Collaboration: B. Abbott, et al Comments: 20 pages, 12 figures, to be submitted to Phys. Rev. D Report-no: LIGO-P040024-04-Z We use 373 hours ($\approx$ 15 days) of data from the second science run of the LIGO gravitational-wave detectors to search for signals from binary neutron star coalescences within a maximum distance of about 1.5 Mpc, a volume of space which includes the Andromeda Galaxy and other galaxies of the Local Group of galaxies. This analysis requires a signal to be found in data from detectors at the two LIGO sites, according to a set of coincidence criteria. The background (accidental coincidence rate) is determined from the data and is used to judge the significance of event candidates. No inspiral gravitational wave events were identified in our search. Using a population model which includes the Local Group, we establish an upper limit of less than 47 inspiral events per year per Milky Way equivalent galaxy with 90% confidence for non-spinning binary neutron star systems with component masses between 1 and 3 $M_\odot$. ----------------------------------------------------------------------------- gr-qc/0505042 From: Duncan Brown Date: Tue, 10 May 2005 02:37:19 GMT (175kb) Search for Gravitational Waves from Primordial Black Hole Binary Coalescences in the Galactic Halo Authors: LIGO Scientific Collaboration: B. Abbott, et al Comments: 7 pages, 4 figures, to be submitted to Phys. Rev. D Report-no: LIGO-P040045-04-Z We use data from the second science run of the LIGO gravitational-wave detectors to search for the gravitational waves from primordial black hole (PBH) binary coalescence with component masses in the range 0.2--$1.0 M_\odot$. The analysis requires a signal to be found in the data from both LIGO observatories, according to a set of coincidence criteria. No inspiral signals were found. Assuming a spherical halo with core radius 5 kpc extending to 50 kpc containing non-spinning black holes with masses in the range 0.2--$1.0 M_\odot$, we place an observational upper limit on the rate of PBH coalescence of 63 per year per Milky Way halo (MWH) with 90% confidence. ----------------------------------------------------------------------------- gr-qc/0505076 From: Matthew Pitkin Date: Mon, 16 May 2005 11:42:51 GMT (62kb) Searching for gravitational waves from known pulsars Authors: Matthew Pitkin, for the LIGO Scientific Collaboration Comments: Accepted by CQG for the proceeding of GWDAW9, 7 pages, 2 figures We present upper limits on the amplitude of gravitational waves from 28 isolated pulsars using data from the second science run of LIGO. The results are also expressed as a constraint on the pulsars' equatorial ellipticities. We discuss a new way of presenting such ellipticity upper limits that takes account of the uncertainties of the pulsar moment of inertia. We also extend our previous method to search for known pulsars in binary systems, of which there are about 80 in the sensitive frequency range of LIGO and GEO 600. ----------------------------------------------------------------------------- gr-qc/0505102 From: Duncan Brown Date: Thu, 19 May 2005 23:45:55 GMT (40kb) Using the INSPIRAL program to search for gravitational waves from low-mass binary inspiral Authors: Duncan A Brown (for the LIGO Scientific Collaboration) Comments: 11 pages, 3 figures, submitted to Classical and Quantum Gravity for the special issue of the GWDAW9 Proceedings The INSPIRAL program is the LIGO Scientific Collaboration's computational engine for the search for gravitational waves from binary neutron stars and sub-solar mass black holes. We describe how this program, which makes use of the FINDCHIRP algorithm (discussed in a companion paper), is integrated into a sophisticated data analysis pipeline that was used in the search for low-mass binary inspirals in data taken during the second LIGO science run. ----------------------------------------------------------------------------- gr-qc/0507081 From: Patrick Sutton Date (v1): Tue, 19 Jul 2005 01:43:57 GMT (389kb) Date (revised v2): Wed, 20 Jul 2005 00:37:41 GMT (351kb) Date (revised v3): Tue, 26 Jul 2005 17:49:15 GMT (318kb) Upper limits from the LIGO and TAMA detectors on the rate of gravitational- wave bursts Authors: LIGO Scientific Collaboration, TAMA Collaboration Comments: 15 pages, 11 figures, to be submitted to Phys Rev D. Updated author list Report-no: LIGO-P040050-06-Z We report on the first joint search for gravitational waves by the TAMA and LIGO collaborations. We looked for millisecond-duration unmodelled gravitational-wave bursts in 473 hr of coincident data collected during early 2003. No candidate signals were found. We set an upper limit of 0.12 events per day on the rate of detectable gravitational-wave bursts, at 90% confidence level. From simulations, we estimate that our detector network was sensitive to bursts with root-sum-square strain amplitude above approximately 1-3x10^{-19} Hz^{-1/2} in the frequency band 700-2000 Hz. We describe the details of this collaborative search, with particular emphasis on its advantages and disadvantages compared to searches by LIGO and TAMA separately using the same data. Benefits include a lower background and longer observation time, at some cost in sensitivity and bandwidth. We also demonstrate techniques for performing coincidence searches with a heterogeneous network of detectors with different noise spectra and orientations. These techniques include using coordinated signal injections to estimate the network sensitivity, and tuning the analysis to maximize the sensitivity and the livetime, subject to constraints on the background. ----------------------------------------------------------------------------- astro-ph/0507254 From: Joseph Romano Date: Mon, 11 Jul 2005 13:53:52 GMT (139kb) Upper Limits on a Stochastic Background of Gravitational Waves Authors: LIGO Scientific Collaboration: B. Abbott, et al Comments: 6 pages, 4 figures The Laser Interferometer Gravitational Wave Observatory (LIGO) has performed a third science run with much improved sensitivities of all three interferometers. We present an analysis of approximately 200 hours of data acquired during this run, used to search for a stochastic background of gravitational radiation. We place upper bounds on the energy density stored as gravitational radiation for three different spectral power laws. For the flat spectrum, our limit of Omega_0<8.4e-4 in the 69-156 Hz band is ~10^5 times lower than the previous result in this frequency range. ----------------------------------------------------------------------------- gr-qc/0508065 From: Alicia M. Sintes Date: Tue, 16 Aug 2005 09:22:26 GMT (863kb) First all-sky upper limits from LIGO on the strength of periodic gravitational waves using the Hough transform Authors: LIGO Scientific Collaboration: B. Abbott, et al Comments: 22 pages, 21 figures, to be submitted to Phys. Rev. D Report-no: LIGO-P050013-03-R We perform a wide parameter space search for continuous gravitational waves over the whole sky and over a large range of values of the frequency and the first spin-down parameter. Our search method is based on the Hough transform, which is a semi-coherent, computationally efficient, and robust pattern recognition technique. We apply this technique to data from the second science run of the LIGO detectors and our final results are all-sky upper limits on the strength of gravitational waves emitted by unknown isolated spinning neutron stars on a set of narrow frequency bands in the range 200-$400 $Hz. The best upper limit on the gravitational wave strain amplitude that we obtain in this frequency range is $4.43\times 10^{-23}$. ----------------------------------------------------------------------------- gr-qc/0509129 From: Eirini Messaritaki Date: Fri, 30 Sep 2005 17:08:23 GMT (528kb) Search for gravitational waves from binary black hole inspirals in LIGO data Authors: LIGO Scientific Collaboration: B. Abbott et. al Comments: 18 pages, 8 figures We report on a search for gravitational waves from binary black hole inspirals in the data from the second science run of the LIGO interferometers. The search focused on binary systems with component masses between 3 and 20 solar masses. Optimally oriented binaries with distances up to 1 Mpc could be detected with efficiency of at least 90%. We found no events that could be identified as gravitational waves in the 385.6 hours of data that we searched. ----------------------------------------------------------------------------- gr-qc/0511146 From: Lindy Blackburn Date: Sun, 27 Nov 2005 22:13:06 GMT (400kb) Search for gravitational wave bursts in LIGO's third science run Authors: LIGO Scientific Collaboration Comments: 12 pages, 6 figures. Amaldi-6 conference proceedings to be published in Classical and Quantum Gravity Report-no: P050043-A-R We report on a search for gravitational wave bursts in data from the three LIGO interferometric detectors during their third science run. The search targets subsecond bursts in the frequency range 100-1100 Hz for which no waveform model is assumed, and has a sensitivity in terms of the root-sum-square (rss) strain amplitude of hrss ~ 10^{-20} / sqrt(Hz). No gravitational wave signals were detected in the 8 days of analyzed data. -----------------------------------------------------------------------------