Subject: ASGRG Newsletter #8 ****************************************************************************** AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION Electronic Newsletter -- #8, Spring 2001 ****************************************************************************** Items for this newsletter should be emailed to the editor: asgrg *AT* hotmail *DOT* com The deadline for the next issue is 31 March, 2002. ****************************************************************************** CONTENTS: * 2002 AIP CONGRESS, Sydney, 8-11 July, 2002 * REPORT ON ACGRG3, Perth, 11-13 July, 2001 * MINUTES OF BIENNIAL GENERAL MEETING, Perth, 11 July, 2001 * DEATH OF NOEL DOUGHTY * MEMBERSHIP DETAILS ONLINE at http://www.physics.adelaide.edu.au/ASGRG/members.html * SUBSCRIPTIONS * FORTHCOMING MEETINGS * MEMBERS' ABSTRACTS at gr-qc, March 2001 – November 2001 ****************************************************************************** 2002 CONGRESS OF THE AUSTRALIAN INSTITUTE OF PHYSICS The 15th Biennial Congress of the Australian Institute of Physics is to be held at the Sydney Convention and Exhibition Centre, Darling Harbour, Sydney from the 8th to the 11th of July 2002. The ASGRG Interest Group has nominated Prof Barry Barish from CalTech, Director of LIGO, as our Plenary Speaker. We are now calling for papers to be presented as part of the ASGRG Interest Group's contribution. The Call for Papers appeared in the November edition of the Australian Physicist, and abstracts should be submitted through the Congress web site, which is at http://www.aip.org.au/Congress2002 The closing date for submission of abstracts is the 15th of February 2002. See the web site for further information on the Congress. ****************************************************************************** REPORT ON ACGRG3, Perth, July 11-13 2001 ACGRG3, the third in the roughly biennial sequence of conferences so far organized by the Society, was held at the University of Western Australia from July 11 to July 13 this year, in tandem with the 4th Edoardo Amaldi Conference on Gravitational Waves. At total of 18 presentations were given over the three days of ACGRG3, including invited talks from Matt Visser ("Analog Gravity"), Hugh Luckock ("Dirac Observables and the Phase Space of General Relativity"), Neil Cornish ("Chaos and Gravitational Waves"), Adrian Gentle ("Regge Calculus") and Peter Szekeres ("The Hubble Index"). Special mention should also be given to Bernard Whiting, who at extremely short notice contributed a talk on algebraically special perturbations in gravity wave research to fill a gap caused by a late withdrawal. The more technical presentations included three talks on gravito- electrodynamics from the Monash group, talks on the abstract boundary and GRworkbench from the ANU group, plus talks on the effective action of a self-interacting scalar field, axisymmetric vacuum gravitation, quintessence, process physics, Gowdy symmetric spacetimes and cosmic strings. The Conference Excursion on July 12 involved a quick lunch and walk around the Yanchep National Park north of Perth, followed by an afternoon exploring the Australian International Gravitational Observatory (AIGO), which included an opportunity to sample some of the wares of the local wineries. The Conference Banquet, a spit roast dinner, was held in an enormous marquee in a paddock just outside the town of Gingin. The last day of ACGRG3 was marked by a dinner in honour of Peter Szekeres at a charming French restaurant on the Stirling Highway. ****************************************************************************** MINUTES OF THE 3RD BIENNIAL GENERAL MEETING OF THE ASGRG held at the University of Western Australia, Perth, 11 July, 2001 The meeting opened at 5.40 p.m. Apologies: David Blair 1. The minutes of the 2nd Biennial General Meeting, held at the University of Sydney, 8 July 1998, were presented to the meeting. Tony Lun moved that the minutes be accepted, and Peter Szekeres seconded. The motion was approved. 2. President's Report: David McClelland informed the meeting that the ASGRG had been given Cognate Society Status with the Australian Institute of Physics at the beginning of 2000. He urged all ASGRG members to join the AIP (the fee is $150). He also raised the possibility that the ASGRG should become a member of FASTS, but no decision was made on this. David briefly mentioned the most recent activity of the Society, namely the ASGRG workshop attached to the AIP Congress in Adelaide in December 2000. The ASGRG partly sponsored the attendance of John Barrow at AIP 2000 as a plenary invited speaker. On another front, three ASGRG committee members attended the first Science Meets Parliament Day, but all declined to attend the second. David reported that the Society's numbers have remained roughly constant since 1998, although relativity research remains in a dire state in Australia. David Wiltshire and Peter Szekeres were leaving Adelaide University without replacement, while Adrian Gentle had moved to Los Alamos and Malcolm Anderson to Brunei. No funding was forthcoming for the national gravity wave facility, and no action had yet been taken on assigning a separate ARC Category Code to general relativity, gravitation and cosmology (the ARC programme manager responsible for this is Laurie Cram). Finally, David suggested that the ASGRG Newsletter continue to be published on a half-yearly basis. Tony Lun added that the ASGRG had been commended by the AIP for bidding for the 17th International Conference of the ISGRG (GR17). 3. Treasurer's Report: Susan Scott reported that the Society's funds had increased from $3,398 on 16 June 1998 to $11,393 on 21 June 2001, although the latter figure included a debt of about $1000 to the ANU Department of Physics. This striking increase in the Society's funds was due almost entirely to the accumulation of membership fees. Currently the ASGRG had 21 Life Members (who had each paid $250), 20 Ordinary Members (each paying $30 a year) and 4 Retired, 15 Student and 3 Unwaged Members (each paying $15 a year). According to Sue, ACGRG2 (Sydney, 1998) had returned a profit of $1488, while she expected ACGRG3 (Perth, 2001) to either lose money or break even. The outstanding costs of ACGRG3 included $1000 to the UWA Adminstrator, $25 per person for the conference excursion, and $450 for the five tea breaks. In addition, the ASGRG contributed $800 of the $3000 sponsorship extended to John Barrow for his attendance at AIP 2000. 4. Auditor's Report: A letter from the Auditor, Hugh Luckock, stating that he was satisfied with the Society's accounts was tabled before the meeting and accepted. The suggestion was made that a life membership lottery should be offered to anyone who joins the ASGRG in the next two years, but no decision was made on this. 5. Appointment of Auditor for the next session: John Schutz agreed to become the next Auditor of the Society's accounts. 6. Election of officers: The following people were elected officers of the ASGRG Committee by acclamation (the mover and seconder are shown in brackets): President: David McClelland (Searle, Shaddock) Treasurer: Susan Scott (McClelland, Shaddock) Secretary: Malcolm Anderson (Wiltshire, Whiting) Officer: David Wiltshire (Charlton, Luckock) Officer: Peter Szekeres (Wiltshire, Whiting) 7. Invited Speaker for AIP 2002 Congress, July 2002: The meeting decided to ask Barry Barish, the Director of the LIGO Project, to become the ASGRG Interest Group's Invited Speaker at the AIP 2002 Congress in July 2002, with Kip Thorne as a second choice. 8. Date and venue for ACGRG4: The meeting decided (tentatively) that ACGRG4 would be held at Monash University in December 2003 or January 2004. 9. Co-option of further committee members: In view of the decisions reported in items 7 and 8 above, the meeting moved to co-opt Tony Lun of Monash University and (in absentia) John Steele of UNSW as extraordinary members of the ASGRG Committee. 10. Bid for GR17, Cairns, 2004: Susan Scott entertained the meeting with a preview of the bid for GR17 that the ASGRG was about to make at the forthcoming GR16 meeting in Durban. The proposed venue was the Cairns Convention Centre, and the proposed date the first week of July 2004. Sue anticipated that between 500 and 700 delegates would attend. With a registration fee of around $600 per delegate, the weekly hire cost of $34,000 for the Convention Centre would be more than adequately covered. [Unfortunately, the ASGRG bid lost out at Durban, and GR17 went to Dublin.] 11. Other business: Peter Szekeres was appointed editor of the proceedings of ACGRG3, which are to appear in General Relativity and Gravitation. The deadline for manuscripts was nominated as the end of October [but has since been changed to the end of November]. The meeting closed at 7 p.m. ****************************************************************************** DEATH OF NOEL DOUGHTY It is with great sadness that we have to report the tragic death of Noel A Doughty, aged 62, who recently took early retirement from the Department of Physics and Astronomy at the University of Canterbury, Christchurch, New Zealand. Noel is well known for his textbook "Lagrangian Interaction – An Introduction to Relativistic Symmetry in Electrodynamics and Gravitation" and is fondly remembered by many former students scattered around the world, who were inspired to undertake careers in theoretical physics by Noel's enthusiasm, his friendly help as a supervisor, and his unique and original approach to his lectures. He will be deeply missed. David Wiltshire Amanda Peet Richard Easther ****************************************************************************** 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 new version of the membership script programs will 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 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 2001 – June 2002 subscriptions are requested, if you wish to pay for July 2002 – June 2003 at the same time, it may simplify matters. ****************************************************************************** FORTHCOMING MEETINGS June 10-11, 2002: BritGravII Queen Mary College, London, UK June 22-July 3, 2002: XIV Petrov School: Recent Problems in Theoretical and Mathematical Physics Kazan, Tatarstan, Russia http://www.kcn.ru/petrov_school July 1-5, 2002: XVIIIth IAP Colloquium: On the Nature of Dark Energy Institut d'Astrophysique de Paris, France http://www.iap.fr/Conferences/Colloque/col2002 July 1-10, 2002: GRG11: Theoretical and Experimental Problems of GR Tomsk, Russia July 8-11, 2002: 15th Biennial Congress of the Australian Institute of Physics Darling Harbour, Sydney, Australia http://www.aip.org.au/Congress2002 July 29-August 10, 2002: 50 Years of the Cauchy Problem in General Relativity Cargese, Corsica, France http://www.phys.univ-tours.fr/%7Epiotr/cargese/announcement November 15-18, 2002: Brane World 2 Kyoto, Japan 2003: 10th Marcel Grossmann Meeting on General Relativity Rio de Janeiro, Brazil http://www.icra.it/MG/mg10/Welcome.htm Dec 2003/Jan 2004: 4th Conference of the ASGRG (ACGRG4) Monash University, Melbourne, Australia July 2004: 17th International Conference of the ISGRG (GR 17) Dublin, Ireland ****************************************************************************** MEMBERS' ABSTRACTS at gr-qc, March 2001 - November 2001 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. ----------------------------------------------------------------------------- Paper: gr-qc/0110028 From: Alan Barnes Date: Thu, 4 Oct 2001 21:15:02 GMT (12kb) Title: Ricci Collineations in Friedmann-Robertson-Walker Spacetimes Authors: Ugur Camci, Alan Barnes Comments: 14 pages, plain TeX, no figures Ricci collineations and Ricci inheritance collineations of Friedmann- Robertson-Walker spacetimes are considered. When the Ricci tensor is non-degenerate, it is shown that the spacetime always admits a fifteen parameter group of Ricci inheritance collineations; this is the maximal possible dimension for spacetime manifolds. The general form of the vector generating the symmetry is exhibited. It is also shown, in the generic case, that the group of Ricci collineations is six-dimensional and coincides with the isometry group. In special cases the spacetime may admit either one or four proper Ricci collineations in addition to the six isometries. These special cases are classified and the general form of the vector fields generating the Ricci collineations is exhibited. When the Ricci tensor is degenerate, the groups of Ricci inheritance collineations and Ricci collineations are infinite-dimensional. General forms for the generating vectors are obtained. Similar results are obtained for matter collineations and matter inheritance collineations. ----------------------------------------------------------------------------- Paper: gr-qc/0109037 From: Alan Barnes Date: Tue, 11 Sep 2001 14:02:12 GMT (6kb) Title: On the Symmetries of the Edgar-Ludwig Metric Authors: Alan Barnes Comments: Plain TeX, 7 pages, No figures The conformal Killing equations for the most general (non-plane wave) conformally flat pure radiation field are solved to find the conformal Killing vectors. As expected fifteen independent conformal Killing vectors exist, but in general the metric admits no Killing or homothetic vectors. However for certain special cases a one-dimensional group of homotheties or motions may exist and in one very special case, overlooked by previous investigators, a two-dimensional homethety group exists. No higher dimensional groups of motions or homotheties are admitted by these metrics. ----------------------------------------------------------------------------- Paper: gr-qc/0109036 From: Alan Barnes Date: Tue, 11 Sep 2001 13:43:22 GMT (9kb) Title: Some Restrictions on Symmetry Groups of Axially Symmetric Spacetimes Authors: Alan Barnes Comments: Plain TeX, 11 pages. No figures Lie transformation groups containing a one-dimensional subgroup acting cyclically on a manifold are considered. The structure of the group is found to be considerably restricted by the existence of a one- dimensional subgroup whose orbits are circles. The results proved do not depend on the dimension of the manifold nor on the existence of a metric, but merely on the fact that the Lie group acts globally on the manifold. Firstly some results for the general case of an $m+1$- dimensional Lie group are derived: those commutators of the associated Lie algebra involving the generator of the cyclic subgroup, $X_0$ say, are severely restricted and, in a suitably chosen basis, take a simple form. The Jacobi identities involving $X_0$ are then applied to show there are further restrictions on the structure of the Lie algebra. All Lie algebras of dimensions 2 and 3 compatible with cyclic symmetry are obtained. In the two-dimensional case the group must be Abelian. For the three-dimensional case, the Bianchi type of the Lie algebra must be I, II, III, VII$_0$, VIII or IX and furthermore in all cases the vector $X_0$ forms part of a basis in which the algebra takes its canonical form. Finally four-dimensional Lie algebras compatible with cyclic symmetry are considered and the results are related to the Petrov- Kruchkovich classification of all four-dimensional Lie algebras. ----------------------------------------------------------------------------- Paper: gr-qc/0111075 From: Zhang Chengmin Date: Thu, 22 Nov 2001 10:23:14 GMT (8kb) Title: Rotation intrinsic spin coupling--the parallelism description Authors: C.M. Zhang, A. Beesham Comments: 10 pages, no figure For the Dirac particle in the rotational system, the rotation induced inertia effect is analogously treated as the modification of the "spin connection" on the Dirac equation in the flat spacetime, which is determined by the equivalent tetrad. From the point of view of parallelism description of spacetime, the obtained torsion axial-vector is just the rotational angular velocity, which is included in the "spin connection". Furthermore the axial-vector spin coupling induced spin precession is just the rotation-spin(1/2) interaction predicted by Mashhoon. Our derivation treatment is straightforward and simplified in the geometrical meaning and physical conception, however the obtained conclusions are consistent with that of the other previous work. ----------------------------------------------------------------------------- Paper: gr-qc/0108011 From: SG Ghosh Date: Fri, 3 Aug 2001 06:45:39 GMT (15kb) Title: Higher dimensional inhomogeneous dust collapse and cosmic censorship Authors: S G Ghosh (Science College, Nagpur, India), A Beesham (University of Zululand, RSA) Comments: 15 pages, LaTeX, 1 figure, 2 tables Journal-ref: Phys.Rev. D64 (2001) 124005 We investigate the occurrence and nature of a naked singularity in the gravitational collapse of an inhomogeneous dust cloud described by higher dimensional Tolman-Bondi space-times. The naked singularities are found to be gravitationally strong in the sense of Tipler. Higher dimensions seem to favour black holes rather than naked singularities. ----------------------------------------------------------------------------- Paper: gr-qc/0106083 From: abeesham Date: Tue, 26 Jun 2001 12:58:37 GMT (8kb) Title: Collapsing shells of radiation in higher dimensional space-time and the cosmic censorship conjecture Authors: S G Ghosh (Science College, Nagpur, India), R V Saraykar (Nagpur University, India), A Beesham (Univesity of Zululand, South Africa) Comments: 9 pages, latex, no figures, accepted in IJMPA Journal-ref: Int.J.Mod.Phys. A16 (2001) 4481-4488 Gravitational collapse of radiation shells in a non self-similar higher dimensional spherically symmetric spacetime is studied. Strong curvature naked singularities form for a highly inhomogeneous collapse, violating the cosmic censorship conjecture. As a special case, self similar models can be constructed. ----------------------------------------------------------------------------- Paper: gr-qc/0110117 From: Reg Cahill Date: Mon, 29 Oct 2001 00:41:25 GMT (35kb) Title: Process Physics: Inertia, Gravity and the Quantum Authors: Reginald T. Cahill (Flinders University, Australia) Comments: LaTex, 18 pages 1 eps file. Contribution to the 3rd Australasian Conference on General Relativity and Gravitation, Perth, Australia, July 2001 Process Physics models reality as self-organising relational or semantic information using a self-referentially limited neural network model. This generalises the traditional non-process syntactical modelling of reality by taking account of the limitations and characteristics of self- referential syntactical information systems, discovered by Goedel and Chaitin, and the analogies with the standard quantum formalism and its limitations. In process physics space and quantum physics are emergent and unified, and time is a distinct non-geometric process. Quantum phenomena are caused by fractal topological defects embedded in and forming a growing three-dimensional fractal process-space. Various features of the emergent physics are briefly discussed including: quantum gravity, quantum field theory, limited causality and the Born quantum measurement metarule, inertia, time-dilation effects, gravity and the equivalence principle, a growing universe with a cosmological constant, black holes and event horizons, and the emergence of classicality. ----------------------------------------------------------------------------- Paper: gr-qc/0106038 From: uzan Date: Mon, 11 Jun 2001 14:47:33 GMT (28kb) Title: Simulated gravity without true gravity in asymmetric brane-world scenarios Authors: Brandon Carter, Jean-Philippe Uzan, Richard A. Battye, Andrew Mennim Comments: Latex, 27 pages Journal-ref: Class.Quant.Grav. 18 (2001) 4871-4896 This article investigates asymmetric brane-world scenarios in the limit when the bulk gravity is negligible. We show that, even when true self gravity is negligible, local mass concentrations will be subject to a mutual attraction force which simulates the effect of Newtonian gravity in the non-relativistic limit. Cosmological and also post-Newtonian constraints are examined. ----------------------------------------------------------------------------- Paper: hep-th/0105091 From: Andrew Mennim Date: Thu, 10 May 2001 15:06:23 GMT (20kb) Title: Einstein equations for an asymmetric brane-world Authors: Richard A. Battye, Brandon Carter, Andrew Mennim, Jean-Philippe Uzan Comments: 14 pages, Revtex Journal-ref: Phys.Rev. D64 (2001) 124007 We consider a brane-world of co-dimension one without the reflection symmetry that is commonly imposed between the two sides of the brane. Using the coordinate-free formalism of the Gauss-Codacci equations, we derive the effective Einstein equations by relating the local curvature to the matter on the brane in the case when its bare tension is much larger than the localized matter, and hence show that Einstein gravity is a natural consequence of such models in the weak field limit. We find agreement with the recently derived cosmological case, which can be solved exactly, and point out that such models can be realized naturally in the case where there is a minimally coupled form field in the bulk. ----------------------------------------------------------------------------- Paper: gr-qc/0106062 From: Neil J. Cornish Date: Wed, 20 Jun 2001 21:31:52 GMT (7kb) Title: Chaos and Gravitational Waves Authors: Neil J. Cornish Comments: 4 pages, no figures Journal-ref: Phys.Rev. D64 (2001) 084011 The gravitational waveforms of a chaotic system will exhibit sensitive dependence on initial conditions. The waveforms of nearby orbits decohere on a timescale fixed by the largest Lyapunov exponent of the orbit. The loss of coherence has important observational consequences for systems where the Lyapunov timescale is short compared to the chirp timescale. Detectors that rely on matched filtering techniques will be unable to detect gravitational waves from these systems. ----------------------------------------------------------------------------- Paper: gr-qc/0106058 From: Neil J. Cornish Date (v1): Mon, 18 Jun 2001 23:05:03 GMT (139kb) Date (revised v2): Mon, 27 Aug 2001 22:23:43 GMT (147kb) Title: Detecting a stochastic gravitational wave background with the Laser Interferometer Space Antenna Authors: Neil J. Cornish Comments: 9 pages, 11 figures. Significant changes to the noise estimates The random superposition of many weak sources will produce a stochastic background of gravitational waves that may dominate the response of the LISA (Laser Interferometer Space Antenna) gravitational wave observatory. Unless something can be done to distinguish between a stochastic background and detector noise, the two will combine to form an effective noise floor for the detector. Two methods have been proposed to solve this problem. The first is to cross- correlate the output of two independent interferometers. The second is an ingenious scheme for monitoring the instrument noise by operating LISA as a Sagnac interferometer. Here we derive the optimal orbital alignment for cross-correlating a pair of LISA detectors, and provide the first analytic derivation of the Sagnac sensitivity curve. ----------------------------------------------------------------------------- Paper: astro-ph/0105374 From: Neil J. Cornish Date: Tue, 22 May 2001 21:19:53 GMT (290kb) Title: Mapping the gravitational wave background Authors: Neil J. Cornish Comments: 16 pages, 6 figures. Submitted to CQG Journal-ref: Class.Quant.Grav. 18 (2001) 4277-4292 The gravitational wave sky is expected to have isolated bright sources superimposed on a diffuse gravitational wave background. The background radiation has two components: a confusion limited background from unresolved astrophysical sources; and a cosmological component formed during the birth of the universe. A map of the gravitational wave background can be made by sweeping a gravitational wave detector across the sky. The detector output is a complicated convolution of the sky luminosity distribution, the detector response function and the scan pattern. Here we study the general de- convolution problem, and show how LIGO (Laser Interferometric Gravitational Observatory) and LISA (Laser Interferometer Space Antenna) can be used to detect anisotropies in the gravitational wave background. ----------------------------------------------------------------------------- Paper: gr-qc/0103075 From: Neil J. Cornish Date (v1): Wed, 21 Mar 2001 09:06:28 GMT (179kb) Date (revised v2): Sat, 24 Mar 2001 23:32:51 GMT (180kb) Title: Space missions to detect the cosmic gravitational-wave background Authors: Neil J. Cornish, Shane L. Larson Comments: 22 pages, 7 figures, IOP style, References Added Journal-ref: Class.Quant.Grav. 18 (2001) 3473-3496 It is thought that a stochastic background of gravitational waves was produced during the formation of the universe. A great deal could be learned by measuring this Cosmic Gravitational-wave Background (CGB), but detecting the CGB presents a significant technological challenge. The signal strength is expected to be extremely weak, and there will be competition from unresolved astrophysical foregrounds such as white dwarf binaries. Our goal is to identify the most promising approach to detect the CGB. We study the sensitivities that can be reached using both individual, and cross-correlated pairs of space based interferometers. Our main result is a general, coordinate free formalism for calculating the detector response that applies to arbitrary detector configurations. We use this general formalism to identify some promising designs for a GrAvitational Background Interferometer (GABI) mission. Our conclusion is that detecting the CGB is not out of reach. ----------------------------------------------------------------------------- Paper: gr-qc/0111057 From: Antony C Searle Date: Mon, 19 Nov 2001 00:41:00 GMT (540kb) Title: GRworkbench: A Computational System Based on Differential Geometry Authors: Susan M Scott, Benjamin J K Evans, Antony C Searle Comments: 10 pages, 4 figures, submitted to Proceedings of the Ninth Marcel Grossmann Meeting We have developed a new tool for numerical work in General Relativity: GRworkbench. While past tools have been ad hoc, GRworkbench closely follows the framework of Differential Geometry to provide a robust and general way of computing on analytically defined space-times. We discuss the relationship between Differential Geometry and C++ classes in GRworkbench, and demonstrate their utility. ----------------------------------------------------------------------------- Paper: gr-qc/0110053 From: Antony C Searle Date: Wed, 10 Oct 2001 00:33:31 GMT (562kb) Title: Network sensitivity to geographical configuration Authors: Antony C Searle, Susan M Scott, David E McClelland Comments: 7 pages, 4 figures, to appear in the proceedings of the 4th Edoardo Amaldi conference Gravitational wave astronomy will require the coordinated analysis of data from the global network of gravitational wave observatories. Questions of how to optimally configure the global network naturally arise in this context. We propose a formalism to compare different configurations of the network, using both the coincident network analysis method and the coherent network analysis method, and construct a model to compute a figure-of-merit based on the detection rate for a population of standard-candle binary inspirals. We find that this measure of network quality is very sensitive to the geographic location of component detectors under a coincident network analysis, but comparatively insensitive under a coherent network analysis. ----------------------------------------------------------------------------- Paper: gr-qc/0108005 From: Geoffery Ericksson Date: Thu, 2 Aug 2001 07:53:26 GMT (17kb) Title: Isotropic singularities in shear-free perfect fluid cosmologies Authors: Geoffery Ericksson, Susan M. Scott Comments: 21 pages, 1 figure Journal-ref: Gen.Rel.Grav. 32 (2000) 425-443 We investigate barotropic perfect fluid cosmologies which admit an isotropic singularity. From the General Vorticity Result of Scott, it is known that these cosmologies must be irrotational. In this paper we prove, using two different methods, that if we make the additional assumption that the perfect fluid is shear-free, then the fluid flow must be geodesic. This then implies that the only shear-free, barotropic, perfect fluid cosmologies which admit an isotropic singularity are the FRW models. ----------------------------------------------------------------------------- Paper: astro-ph/0107321 From: Nelson Nunes Date: Tue, 17 Jul 2001 20:57:52 GMT (75kb) Title: Applications of scalar attractor solutions to Cosmology Authors: S.C.C. Ng (Adelaide), N.J. Nunes (Sussex), F. Rosati (Padova) Comments: 9 pages, 7 figures. Accepted for publication in PRD Report-no: SUSX-TH/01-030 Journal-ref: Phys.Rev. D64 (2001) 083510 We develop a framework to study the phase space of a system consisting of a scalar field rolling down an arbitrary potential with varying slope and a background fluid, in a cosmological setting. We give analytical approximate solutions of the field evolution and discuss applications of its features to the issues of quintessence, moduli stabilisation and quintessential inflation. ----------------------------------------------------------------------------- Paper: astro-ph/0107142 From: David Wiltshire Date (v1): Sun, 8 Jul 2001 03:30:06 GMT (141kb) Date (revised v2): Wed, 12 Sep 2001 09:56:45 GMT (193kb) Title: Future supernova probes of quintessence Authors: S.C.C. Ng, D.L. Wiltshire Comments: 13 pages, RevTeX, 7 figures in 9 files, epsf. Revised: statistical tests extended and refined, but conclusions not significantly changed; references and new figures added Report-no: ADP-01-21/M97 We investigate the potential of a future supernovae data set, as might be obtained by the proposed SNAP satellite, to discriminate between two possible explanations for the observed dimming of the high redshift type IA supernovae, namely either (i) a cosmological evolution for which the expansion of the universe has been accelerating for a substantial range of redshifts $z\goesas1$; or (ii) an unexpected supernova luminosity evolution over such a redshift range. By evaluating Bayes factors we show that within the context of spatially flat model universes with a dark energy the future SNAP data set should be able to discriminate these two possibilities. Our calculations assume particular cosmological models with a quintessence field in the form of a dynamical pseudo Nambu-Goldstone boson (PNGB), and a simple empirical model of the evolution of peak luminosities of the supernovae sources which has been recently discussed in the literature. We also show that the fiducial SNAP data set, simulated with the assumption of no source evolution, is able to discriminate the PNGB model from a number of other spatially flat quintessence models which have been widely studied in the literature, namely those with inverse power-law, simple exponential and double-exponential potentials. ----------------------------------------------------------------------------- Paper: gr-qc/0111059 From: Stefano Liberati Date: Mon, 19 Nov 2001 18:25:12 GMT (26kb) Title: Refringence, field theory, and normal modes Authors: C. Barcelo (Portsmouth U.), S. Liberati (Maryland U.), Matt Visser (Washington U., St. Louis) Comments: 18 pages, RevTex4 In a previous paper [gr-qc/0104001; Class. Quant. Grav. 18 (2001) 3595-3610] we have shown that the occurrence of curved spacetime ``effective Lorentzian geometries'' is a generic result of linearizing an arbitrary classical field theory around some non-trivial background configuration. This observation explains the ubiquitous nature of the ``analog models'' for general relativity that have recently been developed based on condensed matter physics. In the simple (single scalar field) situation analyzed in our previous paper, there is a single unique effective metric; more complicated situations can lead to bi- metric and multi-metric theories. In the present paper we will investigate the conditions required to keep the situation under control and compatible with experiment -- either by enforcing a unique effective metric (as would be required to be strictly compatible with the Einstein Equivalence Principle), or at the worst by arranging things so that there are multiple metrics that are all ``close'' to each other (in order to be compatible with the {\Eotvos} experiment). The algebraically most general situation leads to a physical model whose mathematical description requires an extension of the usual notion of Finsler geometry to a Lorentzian-signature pseudo-Finsler geometry; while this is possibly of some interest in its own right, this particular case does not seem to be immediately relevant for either particle physics or gravitation. The key result is that wide classes of theories lend themselves to an effective metric description. This observation provides further evidence that the notion of ``analog gravity'' is rather generic. ----------------------------------------------------------------------------- Paper: cond-mat/0110211 From: Uwe R. Fischer Date: Wed, 10 Oct 2001 18:11:14 GMT (15kb) Title: Riemannian geometry of irrotational vortex acoustics Authors: Uwe R. Fischer, Matt Visser Comments: 4 pages, 2 figures, RevTex4 We consider acoustic propagation in an irrotational vortex, using the technical machinery of differential geometry to investigate the ``acoustic geometry'' that is probed by the sound waves. The acoustic space-time curvature of a constant circulation hydrodynamical vortex leads to deflection of phonons at appreciable distances from the vortex core. The scattering angle for phonon rays is shown to be quadratic in the small quantity $\Gamma/(2\pi cb)$, where $\Gamma$ is the vortex circulation, $c$ the speed of sound, and $b$ the impact parameter. ----------------------------------------------------------------------------- Paper: gr-qc/0110036 From: visser@tui.wustl.edu (Matt Visser) Date: Sat, 6 Oct 2001 19:10:22 GMT (19kb) Title: Towards the observation of Hawking radiation in Bose--Einstein condensates Authors: Carlos Barcelo (Washington University in Saint Louis) Stefano Liberati (University of Maryland), Matt Visser (Washington University in Saint Louis) Comments: revtex4; 5 pages in double-column format Acoustic analogues of black holes (dumb holes) are generated when a supersonic fluid flow entrains sound waves and forms a trapped region from which sound cannot escape. The surface of no return, the acoustic horizon, is qualitatively very similar to the event horizon of a general relativity black hole. In particular Hawking radiation (a thermal bath of phonons with temperature proportional to the ``surface gravity'') is expected to occur. In this note we consider quasi-one-dimensional supersonic flow of a Bose--Einstein condensate (BEC) in a Laval nozzle (converging-diverging nozzle), with a view to finding which experimental settings could magnify this effect and provide an observable signal. We identify an experimentally plausible configuration with a Hawking temperature of order 70 n K; to be contrasted with a condensation temperature of the order of 90 n K. ----------------------------------------------------------------------------- Paper: gr-qc/0109069 From: Sayan Kar Date: Wed, 19 Sep 2001 17:00:02 GMT (16kb) Title: R=0 spacetimes and self-dual Lorentzian wormholes Authors: Naresh Dadhich (IUCAA), Sayan Kar (IITKgp), Sailajananda Mukherji (NBU), Matt Visser (Washington) Comments: 8 pages, RevTex two column, one figure A two-parameter family of spherically symmetric, static Lorentzian wormholes is obtained as the general solution of the equation $\rho=\rho_t=0$, where $\rho = T_{ij} u^iu^j$, $\rho_t = (T_{ij} - {1\over2} T g_{ij}) u^iu^j$, and $u^i u_i =- 1$. This equation characterizes a class of spacetimes which are ``self dual'' (in the sense of electrogravity duality). The class includes the Schwarzschild black hole, a family of naked singularities, and a disjoint family of Lorentzian wormholes, all of which have vanishing scalar curvature (R=0). Properties of these spacetimes are discussed. Using isotropic coordinates we delineate clearly the domains of parameter space for which wormholes, nakedly singular spacetimes and the Schwarzschild black hole can be obtained. A model for the required ``exotic'' stress- energy is discussed, and the notion of traversability for the wormholes is also examined. ----------------------------------------------------------------------------- Paper: hep-th/0109033 From: visser@tui.wustl.edu (Matt Visser) Date: Wed, 5 Sep 2001 22:27:49 GMT (6kb) Title: Acoustics in Bose--Einstein condensates as an example of Lorentz symmetry breaking Authors: Matt Visser (Washington University in Saint Louis), Carlos Barcelo (Washington University in Saint Louis), Stefano Liberati (U Maryland) Comments: Presented at CPT01; the Second Meeting on CPT and Lorentz Symmetry; Bloomington, Indiana; 15--18 Aug 2001. 6 pages. Uses sprocl.sty (World Scientific style file; Latex 209) To help focus ideas regarding possible routes to the breakdown of Lorentz invariance, it is extremely useful to explore concrete physical models that exhibit similar phenomena. In particular, acoustics in Bose- -Einstein condensates has the interesting property that at low- momentum the phonon dispersion relation can be written in a ``relativistic'' form exhibiting an approximate ``Lorentz invariance''. Indeed all of low-momentum phonon physics in this system can be reformulated in terms of relativistic curved-space quantum field theory. In contrast, high-momentum phonon physics probes regions where the dispersion relation departs from the relativistic form and thus violates Lorentz invariance. This model provides a road-map of at least one route to broken Lorentz invariance. Since the underlying theory is manifestly physical this type of breaking automatically avoids unphysical features such as causality violations. This model hints at the type of dispersion relation that might be expected at ultra-high energies, close to the Planck scale, where quantum gravity effects are suspected to possibly break ordinary Lorentz invariance. ----------------------------------------------------------------------------- Paper: gr-qc/0107091 From: visser@tui.wustl.edu (Matt Visser) Date: Fri, 27 Jul 2001 21:37:42 GMT (31kb) Title: Faster-than-c signals, special relativity, and causality Authors: Stefano Liberati (U Maryland), Sebastiano Sonego (U Udine, Italy), Matt Visser (Washington University in Saint Louis) Comments: Plain LaTeX2E; 25 pages Motivated by the recent attention on superluminal phenomena, we investigate the compatibility between faster-than-c propagation and the fundamental principles of relativity and causality. We first argue that special relativity can easily accommodate --- indeed, does not exclude - -- faster-than-c signalling at the kinematical level. As far as causality is concerned, it is impossible to make statements of general validity, without specifying at least some features of the tachyonic propagation. We thus focus on the Scharnhorst effect (faster-than-c photon propagation in the Casimir vacuum), which is perhaps the most plausible candidate for a physically sound realization of these phenomena. We demonstrate that in this case the faster-than-c aspects are ``benign'' and constrained in such a manner as to not automatically lead to causality violations. ----------------------------------------------------------------------------- Paper: cond-mat/0106255 From: Michael Stone Date: Wed, 13 Jun 2001 21:02:14 GMT (18kb) Title: Wave Equation for Sound in Fluids with Vorticity Authors: Santiago Esteban Perez Bergliaffa, Katrina Hibberd, Michael Stone, Matt Visser Comments: RevTeX, 27pages Subj-class: Condensed Matter; Fluid Dynamics We use Clebsch potentials and an action principle to derive a closed system of gauge invariant equations for sound superposed on a general background flow. Our system reduces to the Unruh (1981) and Pierce (1990) wave equations when the flow is irrotational, or slowly varying. We illustrate our formalism by applying it to waves propagating in a uniformly rotating fluid where the sound modes hybridize with inertial waves. ----------------------------------------------------------------------------- Paper: hep-th/0106111 From: visser@tui.wustl.edu (Matt Visser) Date: Wed, 13 Jun 2001 22:53:41 GMT (15kb) Title: Essential and inessential features of Hawking radiation Authors: Matt Visser (Washington University in Saint Louis) Comments: JHEP style; 17 pages There are numerous derivations of the Hawking effect available in the literature. They emphasise different features of the process, and sometimes make markedly different physical assumptions. This article presents a ``minimalist'' argument, and strips the derivation of as much excess baggage as possible. All that is really necessary is quantum physics plus a slowly evolving future apparent horizon (*not* an event horizon). In particular, neither the Einstein equations nor Bekenstein entropy are necessary (nor even useful) in deriving Hawking radiation. ----------------------------------------------------------------------------- Paper: gr-qc/0106002 From: Stefano Liberati Date: Fri, 1 Jun 2001 20:23:44 GMT (8kb) Title: Einstein Gravity as an emergent phenomenon? Authors: Carlos Barcelo, Matt Visser, Stefano Liberati Comments: 8 pages, Essay awarded an honorable mention in the year 2001 Gravity Research Foundation essay competition In this essay we marshal evidence suggesting that Einstein gravity may be an emergent phenomenon, one that is not ``fundamental'' but rather is an almost automatic low-energy long-distance consequence of a wide class of theories. Specifically, the emergence of a curved spacetime ``effective Lorentzian geometry'' is a common generic result of linearizing a classical scalar field theory around some non-trivial background. This explains why so many different ``analog models'' of general relativity have recently been developed based on condensed matter physics; there is something more fundamental going on. Upon quantizing the linearized fluctuations around this background geometry, the one-loop effective action is guaranteed to contain a term proportional to the Einstein--Hilbert action of general relativity, suggesting that while classical physics is responsible for generating an ``effective geometry'', quantum physics can be argued to induce an ``effective dynamics''. This physical picture suggests that Einstein gravity is an emergent low-energy long-distance phenomenon that is insensitive to the details of the high-energy short-distance physics. ----------------------------------------------------------------------------- Paper: gr-qc/0104001 From: visser@tui.wustl.edu (Matt Visser) Date: Mon, 2 Apr 2001 20:45:27 GMT (20kb) Title: Analog gravity from field theory normal modes? Authors: Carlos Barcelo (Washington University in Saint Louis) Stefano Liberati (University of Maryland), Matt Visser (Washington University in Saint Louis) Comments: Revtex 4 (beta 5); 12 pages in single-column format Journal-ref: Class.Quant.Grav. 18 (2001) 3595-3610 We demonstrate that the emergence of a curved spacetime ``effective Lorentzian geometry'' is a common and generic result of linearizing a field theory around some non-trivial background. This investigation is motivated by considering the large number of ``analog models'' of general relativity that have recently been developed based on condensed matter physics, and asking whether there is something more fundamental going on. Indeed, linearization of a classical field theory (a field theoretic ``normal mode analysis'') results in fluctuations whose propagation is governed by a Lorentzian-signature curved spacetime ``effective metric''. For a single scalar field, this procedure results in a unique effective metric, which is quite sufficient for simulating kinematic aspects of general relativity (up to and including Hawking radiation). Quantizing the linearized fluctuations, the one-loop effective action contains a term proportional to the Einstein--Hilbert action, suggesting that while classical physics is responsible for generating an ``effective geometry'', quantum physics can be argued to induce an ``effective dynamics''. The situation is strongly reminiscent of Sakharov's ``induced gravity'' scenario, and suggests that Einstein gravity is an emergent low-energy long-distance phenomenon that is insensitive to the details of the high-energy short-distance physics. (We mean this in the same sense that hydrodynamics is a long-distance emergent phenomenon, many of whose predictions are insensitive to the short-distance cutoff implicit in molecular dynamics.) ----------------------------------------------------------------------------- Paper: gr-qc/0103065 From: visser@tui.wustl.edu (Matt Visser) Date (v1): Fri, 16 Mar 2001 22:17:43 GMT (12kb) Date (revised v2): Wed, 22 Aug 2001 20:13:24 GMT (16kb) Title: Spacetime geometry of static fluid spheres Authors: Shahinur Rahman, Matt Visser (Washington University in Saint Louis) Comments: Plain LaTeX 2e --- v2: now 22 pages; minor presentation changes in the first part of the paper - -- no physics modifications; major additions to the examples section: the Gold-I solution is shown to be identical to the G-G solution. The interior Schwarzschild, Stewart, Buch5 XIII, de Sitter, anti-de Sitter, and Einstein solutions are all special cases We exhibit a simple and explicit formula for the metric of an arbitrary static spherically symmetric perfect fluid spacetime. This class of metrics depends on one freely specifiable monotone non-increasing generating function. We also investigate various regularity conditions, and the constraints they impose. Because we never make any assumptions as to the nature (or even the existence) of an equation of state, this technique is useful in situations where the equation of state is for whatever reason uncertain or unknown. To illustrate the power of the method we exhibit a new form of the ``Goldman--I'' exact solution and calculate its total mass. This is a three-parameter closed-form exact solution given in terms of algebraic combinations of quadratics. It interpolates between (and thereby unifies) at least six other reasonably well-known exact solutions. ----------------------------------------------------------------------------- Paper: hep-th/0109099 From: David Wiltshire Date (v1): Wed, 12 Sep 2001 21:32:32 GMT (24kb) Date (revised v2): Wed, 19 Sep 2001 03:06:09 GMT (24kb) Title: Brane worlds with bolts Authors: Jorma Louko, David L. Wiltshire Comments: 18 pages, 1 eps figure, JHEP3 with epsfig; reference added Report-no: ADP-00-45/M93 We construct a family of (p+3)-dimensional brane worlds in which the brane has one compact extra dimension, the bulk has two extra dimensions, and the bulk closes regularly at codimension two submanifolds known as bolts. The (p+1)-dimensional low energy spacetime M_{low} may be any Einstein space with an arbitrary cosmological constant, the value of the bulk cosmological constant is arbitrary, and the only fields are the metric and a bulk Maxwell field. The brane can be chosen to have positive tension, and the closure of the bulk provides a singularity-free boundary condition for solutions that contain black holes or gravitational waves in M_{low}. The spacetimes admit a nonlinear gravitational wave whose properties suggest that the Newtonian gravitational potential on a flat M_{low} will behave essentially as the static potential of a massless minimally coupled scalar field with Neumann boundary conditions. When M_{low} is (p+1)- dimensional Minkowski with p\ge3 and the bulk cosmological constant vanishes, this static scalar potential is shown to have the long distance behaviour characteristic of p spatial dimensions. ----------------------------------------------------------------------------- Paper: hep-th/0109093 From: David Wiltshire Date: Wed, 12 Sep 2001 04:17:34 GMT (62kb) Title: Spacetime as a membrane in higher dimensions Authors: G.W. Gibbons, D.L. Wiltshire Comments: 30 pages, 4 figures in 10 files, epsf. This early brane world paper is being placed on the archive to make it more easily accessible, as its results are used in a new brane world construction in an accompanying submission Journal-ref: Nucl.Phys. B287 (1987) 717 By means of a simple model we investigate the possibility that spacetime is a membrane embedded in higher dimensions. We present cosmological solutions of d-dimensional Einstein-Maxwell theory which compactify to two dimensions. These solutions are analytically continued to obtain dual solutions in which a (d-2)-dimensional Einstein spacetime "membrane" is embedded in d-dimensions. The membrane solutions generalise Melvin's 4-dimensional flux tube solution. The flat membrane is shown to be classically stable. It is shown that there are zero mode solutions of the d-dimensional Dirac equation which are confined to a neighbourhood of the membrane and move within it like massless chiral (d-2)-dimensional fermions. An investigation of the spectrum of scalar perturbations shows that a well- defined mass gap between the zero modes and massive modes can be obtained if there is a positive cosmological term in (d-2) dimensions or a negative cosmological term in d dimensions. -----------------------------------------------------------------------------