Subject: ASGRG Newsletter #11 ****************************************************************************** AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION Electronic Newsletter -- #11, Autumn 2003 ****************************************************************************** Items for this newsletter should be emailed to the editor: asgrg *AT* hotmail *DOT* com The deadline for the next issue is 31 October, 2003. ****************************************************************************** CONTENTS: * ICIAM 2003, Sydney, 7-11 July, 2003 * ACGRG4, Monash University, 7-9 January, 2004 * MEMBERSHIP DETAILS ONLINE at http://www.physics.adelaide.edu.au/ASGRG/members.html * SUBSCRIPTIONS * FORTHCOMING MEETINGS * MEMBERS' ABSTRACTS at gr-qc, December 2002 - May 2003 ****************************************************************************** ICIAM 2003, Sydney, 7-11 July, 2003 As part of the 6th Australia-New Zealand Mathematics Convention being held in conjunction with ICIAM 2003 at the Sydney Convention and Exhibition Centre in Darling Harbour on 7-11 July 2003, a Relativity Minisymposium organised by John Steele will take place on the morning of Friday 11 July. The four talks comprising the Minisymposium are: 1. Hugh Luckock, University of Sydney "Canonical General Relativity without Constraints" Abstract: General relativity can be formulated in terms of a minimal set of dynamical variables representing physically measurable degrees of freedom, with no residual gauge symmetries other than those associated with Lorentz transformations of the observer's frame of reference. The resulting absence of constraints in the canonical formulation then leads to a simple expression for the symplectic 2-form and suggests a new approach to quantisation, free from the usual problems associated with the role of time and definitions of observables. 2. Tony Lun, Monash University "Purely Gravito-Magnetic Space-times" Abstract: We discuss the evolution of the Einstein equations in ADM formalism from initial data that give rise to purely gravito-electric and purely gravito-magnetic space-times. A number of examples are discussed. 3. Robert Bartnik, University of Canberra "Numerics and formal expansion of spacetime metric near null infinity" Abstract: This talk will explore numerical and formal expansions of the spacetime metric near future null infinity. The main aim is to show that, assuming the Einstein equations are satisfied, the asymptotic Bondi mass is defined and satisfies the Trautman-Bondi mass loss formula under very weak conditions on the null hypersurface metric. 4. John Steele, University of New South Wales "The Einstein Field Equations" Abstract: This talk will cover some general aspects of the mathematical techniques that have been evolved for solving the Einstein Field Equations of classical General Relativity. Some of the history of the methods may also be discussed. ****************************************************************************** 4TH AUSTRALASIAN CONFERENCE ON GENERAL RELATIVITY AND GRAVITATION (ACGRG4) Monash University, Melbourne, 7-9 January 2004 ACGRG4 is the fourth in a series of biennial conferences run by the ASGRG with the aim of bringing together researchers from around the world to discuss new findings in mathematical, theoretical, numerical and experimental gravitation, to make contacts and consolidate ideas. ACGRG4 will be held on the Clayton campus of Monash University, Melbourne from Wednesday January 7 to Friday January 9, 2004. Clayton campus is the largest of Monash University's seven campuses, and is situated about 20 km from the centre of Melbourne and 40 km from Melbourne's Tullamarine International Airport. Papers on any area of general relativity, gravitation or related fields will be welcomed for consideration by the Scientific Organising Committee. Accepted papers will be allocated an estimated 20 minutes of conference time plus 5 minutes for questions. Poster presentations will also be considered. The conference proceedings will subsequently be refereed and published. To submit an abstract for ACGRG4 either contact the ASGRG Secretary, Dr Malcolm Anderson, at manderso@fos.ubd.edu.bn or at asgrg *AT* hotmail *DOT* com The deadline for submission of abstracts is September 30, 2003. The homepage for ACGRG4 can be found at http://www.physics.adelaide.edu.au/ASGRG/ACGRG4/ ****************************************************************************** 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 2003 - June 2004 subscriptions are requested, if you wish to pay for July 2004 - June 2005 at the same time, it may simplify matters. ****************************************************************************** FORTHCOMING MEETINGS May 12 - July 11, 2003: Gravitational Interaction of Compact Objects Kavli Institute for Theoretical Physics, UCSB, USA http://www.itp.ucsb.edu/activities/grav03/?id=18 June 22 - July 3, 2003: Recent Problems in Theoretical and Mathematical Physics (15th Petrov Summer School-Seminar) Tatarstan, Russia http://www.kcn.ru/petrov_school June 23-27, 2003: Hyperbolic Models in Astrophysics and Cosmology Isaac Newton Institute, Cambridge, UK http://www.newton.cam.ac.uk/programmes/NPA/npaw01.html June 23-27, 2003: Gravitation, Cosmology and Relativistic Astrophysics (2nd Gravitational Conference) Kharkov, Ukraine http://www.univer.kharkov.ua/grav2003/eng/index.html July 6-11, 2003: 5th Edoardo Amaldi Conference on Gravitational Waves (Amaldi 5) Pisa Italy http://www.ego-gw.it/Amaldi5/ July 7-11, 2003: 5th International Congress on Industrial and Applied Mathematics (ICIAM 2003) Sydney, Australia http://www.iciam.org/iciamHome/iciamHome_tf.html July 13-26, 2003: IAU XXVth General Assembly (IAUXXV) Sydney, Australia http://www.astronomy2003.com/ July 20-26, 2003: 10th Marcel Grossmann Meeting on General Relativity Rio de Janeiro, Brazil http://www.cbpf.br/mg10/WelcomeNew.html July 21 - August 1, 2003: Graduate Summer School in General Relativistic Hydrodynamics Vancouver, Canada http://cgwp.gravity.psu.edu/events/GRHydro03/ August 7-9, 2003: Tuebingen Workshop on Numeric and Analytic Properties of the Vacuum Einstein Equations Tuebingen, Germany http://www.tat.physik.uni-tuebingen.de/%7Enumrel/workshop-2003/ August 10-15, 2003: 7th Hungarian Relativity Workshop Sarospatak, Hungary http://www.kfki.hu/%7Erw2003/ September 1-10, 2003: Mathematics of Gravitation II Warsaw, Poland http://www.astro.uni.torun.pl/%7Ekb/AllSky/Workshop.html September 1-10, 2003: Problems of Theoretical and Observational Cosmology (3rd Ulyanovsk International School-Seminar, UISS-2003) Ulyanovsk, Russia http://www.rgs.da.ru/ September 11-13, 2003: 27th Spanish Relativity Meeting: Gravitational Radiation Alicante, Spain http://www.sri.ua.es/congresos/ere2003/index.html September 12-14, 2003: 3rd British Gravity Meeting (BritGravIII) Ambleside, English Lake District http://www.lancs.ac.uk/depts/physics/conf/britgrav/ September 15-26: Advanced School and Conference on Sources of Gravitational Waves Trieste, Italy http://www.sissa.it/ap/workshops.html October 17-18, 2003: 13th Midwest Relativity Meeting University of Windsor, Ontario, Canada http://zeus.uwindsor.ca/courses/physics/mwr13/index.html November 6-8, 2003: 3rd Gravitational Wave Phenomenology Workshop (GWPW03) Penn State University, USA http://gravity.psu.edu/mailman/listinfo/gwpw03/ December 1-12, 2003: 2nd Workshop on Formulations of Einstein Equations for Numerical Relativity Mexico City, Mexico http://www.appleswithapples.org/Meetings/Mexico2003/index.html December 14-15, 2003: Inaugural Meeting of the Center for Gravitational Wave Astronomy Brownsville, Texas http://cgwa.phys.utb.edu/ December 17-20, 2003: 8th Annual Gravitational Wave Data Analysis Workshop Wisconsin, USA January 7-9, 2004: 4th Conference of the ASGRG (ACGRG4) Monash University, Melbourne, Australia http://www.physics.adelaide.edu.au/ASGRG/ACGRG4/ July 18-25, 2004: 17th International Conference of the ISGRG (GR 17) Dublin, Ireland ****************************************************************************** MEMBERS' ABSTRACTS at gr-qc, December 2002 - May 2003 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/0212016 From: Alan Barnes Date: Tue, 3 Dec 2002 17:45:49 GMT (6kb) Killing Tensors from Conformal Killing Vectors Authors: A. Barnes, S.B. Edgar, R. Rani Comments: 5 pages, Latex. To appear in the Proceedings of the Spanish Relativity Meeting (Encuentros Relativistas Espanoles), 2002 Some years ago Koutras presented a method of constructing a conformal Killing tensor from a pair of orthogonal conformal Killing vectors. When the vector associated with the conformal Killing tensor is a gradient, a Killing tensor (in general irreducible) can then be constructed. In this paper it is shown that the severe restriction of orthogonality is unnecessary and thus it is possible that many more Killing tensors can be constructed in this way. We also extend, and in one case correct, some results on Killing tensors constructed from a single conformal Killing vector. Weir's result that, for flat space, there are 84 independent conformal Killing tensors, all of which are reducible, is extended to conformally flat spacetimes. In conformally flat spacetimes it is thus possible to construct all the conformal Killing tensors and in particular all the Killing tensors (which in general will not be reducible) from conformal Killing vectors. ----------------------------------------------------------------------------- Paper: gr-qc/0301059 From: Brian Edgar Date (v1): Thu, 16 Jan 2003 16:11:29 GMT (15kb) Date (revised v2): Tue, 21 Jan 2003 20:24:47 GMT (15kb) Date (revised v3): Wed, 12 Mar 2003 16:41:38 GMT (15kb) Killing Tensors and Conformal Killing Tensors from Conformal Killing Vectors Authors: Raffaele Rani, S. Brian Edgar, Alan Barnes Comments: 18 pages References added. Comments and reference to 2-dim case. Typos corrected Journal-ref: Class.Quant.Grav. 20 (2003) 1929-1942 Koutras has proposed some methods to construct reducible proper conformal Killing tensors and Killing tensors (which are, in general, irreducible) when a pair of orthogonal conformal Killing vectors exist in a given space. We give the completely general result demonstrating that this severe restriction of orthogonality is unnecessary. In addition we correct and extend some results concerning Killing tensors constructed from a single conformal Killing vector. A number of examples demonstrate how it is possible to construct a much larger class of reducible proper conformal Killing tensors and Killing tensors than permitted by the Koutras algorithms. In particular, by showing that all conformal Killing tensors are reducible in conformally flat spaces, we have a method of constructing all conformal Killing tensors (including all the Killing tensors which will in general be irreducible) of conformally flat spaces using their conformal Killing vectors. ----------------------------------------------------------------------------- Paper: gr-qc/0305091 From: Alan Barnes Date: Fri, 23 May 2003 18:29:44 GMT (4kb) Comment on "Conformally flat stationary axisymmetric metrics" Authors: Alan Barnes, Jose MM Senovilla Comments: 2 pages Latex Garcia and Campuzano claim to have found a previously overlooked family of stationary and axisymmetric conformally flat spacetimes, contradicting an old theorem of Collinson. In both these papers it is tacitly assumed that the isometry group is orthogonally transitive. Under the same assumption, we point out here that Collinson's result still holds if one demands the existence of an axis of symmetry on which the axial Killing vector vanishes. On the other hand if the assumption of orthogonal transitivity is dropped, a wider class of metrics is allowed and it is possible to find explicit counterexamples to Collinson's result. ----------------------------------------------------------------------------- Paper: astro-ph/0301548 From: Neil J. Cornish Date (v1): Tue, 28 Jan 2003 04:33:06 GMT (493kb) Date (revised v2): Tue, 28 Jan 2003 22:24:26 GMT (466kb) LISA data analysis: Source identification and subtraction Authors: Neil J. Cornish, Shane L. Larson Comments: 15 pages, 17 figures Journal-ref: Phys.Rev. D67 (2003) 103001 The Laser Interferometer Space Antenna (LISA) will operate as an AM/FM receiver for gravitational waves. For binary systems, the source location, orientation and orbital phase are encoded in the amplitude and frequency modulation. The same modulations spread a monochromatic signal over a range of frequencies, making it difficult to identify individual sources. We present a method for detecting and subtracting individual binary signals from a data stream with many overlapping signals. ----------------------------------------------------------------------------- Paper: gr-qc/0304020 From: Neil J. Cornish Date: Fri, 4 Apr 2003 06:40:25 GMT (9kb) Gravitational Wave Confusion Noise Authors: Neil J. Cornish Comments: 4 pages, 1 Figure One of the greatest challenges facing gravitational wave astronomy in the low frequency band is the confusion noise generated by the vast numbers of unresolved galactic and extra galactic binary systems. Estimates of the binary confusion noise suffer from several sources of astrophysical uncertainty, such as the form of the initial mass function and the star formation rate. There is also considerable uncertainty about what defines the confusion limit. Various ad-hoc rules have been proposed, such as the one source per bin rule, and the one source per three bin rule. Here information theoretic methods are used to derive a more realistic estimate for the confusion limit. It is found that the gravitational wave background becomes unresolvable when there is, on average, more than one source per eight frequency bins. This raises the best estimate for the frequency at which galactic binaries become a source of noise from 1.45 mHz to 2.54 mHz. ----------------------------------------------------------------------------- Paper: gr-qc/0304056 From: Janna Levin Date: Tue, 15 Apr 2003 10:19:15 GMT (136kb) Lyapunov timescales and black hole binaries Authors: Neil J. Cornish, Janna Levin Comments: To be published in Classical and Quantum Gravity Journal-ref: Class.Quant.Grav. 20 (2003) 1649-1660 Black holes binaries support unstable orbits at very close separations. In the simplest case of geodesics around a Schwarzschild black hole the orbits, though unstable, are regular. Under perturbation the unstable orbits can become the locus of chaos. All unstable orbits, whether regular or chaotic, can be quantified by their Lyapunov exponents. The exponents are observationally relevant since the phase of gravitational waves can decohere in a Lyapunov time. If the timescale for dissipation due to gravitational waves is shorter than the Lyapunov time, chaos will be damped and essentially unobservable. We find the timescales can be comparable. We emphasize that the Lyapunov exponents must only be used cautiously for several reasons: they are relative and depend on the coordinate system used, they vary from orbit to orbit, and finally they can be deceptively diluted by transient behaviour for orbits which pass in and out of unstable regions. ----------------------------------------------------------------------------- Paper: gr-qc/0305104 From: simon davis Date: Wed, 28 May 2003 14:20:50 GMT (9kb) The Quantum Cosmological Wavefunction at Very Early Times for a Quadratic Gravity Theory Author: Simon Davis Comments: Tex, 13 pages Report-no: University of Potsdam preprint 2003/04 The quantum cosmological wavefunction for a quadratic gravity theory derived from the heterotic string effective action is obtained near the inflationary epoch and during the initial Planck era. Neglecting derivatives with respect to the scalar field, the wavefunction would satisfy a third-order differential equation near the inflationary epoch which has a solution that is singular in the scale factor limit $a(t)\to 0$. When scalar field derivatives are included, a sixth-order differential equation is obtained for the wavefunction and the solution by Mellin transform is regular in the $a\to 0$ limit. It follows that inclusion of the scalar field in the quadratic gravity action is necessary for consistency of the quantum cosmology of the theory at very early times. ----------------------------------------------------------------------------- Paper: gr-qc/0302098 From: Geoffery Ericksson Date: Tue, 25 Feb 2003 00:51:19 GMT (18kb) General properties of cosmological models with an Isotropic Singularity Authors: Geoffery Ericksson, Susan M. Scott Comments: 18 pages, 1 figure Journal-ref: Gen.Rel.Grav. 34 (2002) 1657 Much of the published work regarding the Isotropic Singularity is performed under the assumption that the matter source for the cosmological model is a barotropic perfect fluid, or even a perfect fluid with a $\gamma$-law equation of state. There are, however, some general properties of cosmological models which admit an Isotropic Singularity, irrespective of the matter source. In particular, we show that the Isotropic Singularity is a point-like singularity and that vacuum space-times cannot admit an Isotropic Singularity. The relationships between the Isotropic Singularity, and the energy conditions, and the Hubble parameter is explored. A review of work by the authors, regarding the Isotropic Singularity, is presented. ----------------------------------------------------------------------------- Paper: gr-qc/0302044 From: Warner Miller Date: Wed, 12 Feb 2003 04:02:26 GMT (21kb) Constraints in Quantum Geometrodynamics Authors: Adrian P. Gentle (1), Nathan D. George (1), Arkady Kheyfets (2), Warner A. Miller (1 and 3) ((1) Theoretical Division, Los Alamos National Laboratory, (2) Department of Mathematics, NCSU, (3) Department of Physics, Florida Atlantic University) Comments: 36 pages, no figures, submitted to IJMPA We compare different treatments of the constraints in canonical quantum gravity. The standard approach on the superspace of 3-geometries treats the constraints as the sole carriers of the dynamic content of the theory, thus rendering the traditional dynamic equations obsolete. Quantization of the constraints in both the Dirac and ADM square root Hamiltonian approach lead to the well known problems of the description of time evolution. These problems of time are both of interpretational and technical nature. In contrast, the so-called geometrodynamic quantization procedure on the superspace of the true dynamic variables separates the issue of quantization from enforcing the constraints. The resulting theory takes into account the states that are off shell with respect to the constraints, and thus avoids the problems of time. Here, we develop, for the first time, the geometrodynamic quantization formalism in a general setting and show that it retains all essential features previously illustrated in the context of homogeneous cosmologies. ----------------------------------------------------------------------------- Paper: gr-qc/0302051 From: Warner Miller Date: Thu, 13 Feb 2003 01:05:34 GMT (5kb) The Issue of Time in Quantum Geometrodynamics Authors: Nathan D. George (1), Adrian P. Gentle (1), Arkady Kheyfets (2), Warner A. Miller (1 and 3) ((1)Theoretical Division, Los Alamos National Laboratory (2) Department of Mathematics, North Carolina State University, (3) Department of Physics, Florida Atlantic University) Comments: 4 pages, no figures; To appear in Proceedings of the 24th International Colloquium on Group Theoretical Methods in Physics Standard techniques of canonical gravity quantization on the superspace of 3--metrics are known to cause insurmountable difficulties in the description of time evolution. We forward a new quantization procedure on the superspace of true dynamic variables -- geometrodynamic quantization. This procedure takes into account the states that are ``off-shell'' with respect to the constraints and thus circumvents the notorious problems of time. In this approach quantum geometrodynamics, general covariance, and the interpretation of time emerge together as parts of the solution to the total problem of geometrodynamic evolution. ----------------------------------------------------------------------------- Paper: gr-qc/0303013 From: Massimo Tinto Date: Mon, 3 Mar 2003 19:33:35 GMT (169kb) Implementation of Time-Delay Interferometry for LISA Authors: Massimo Tinto, Daniel A. Shaddock, Julien Sylvestre, J.W. Armstrong Comments: 39 pages, 6 figures, 2 tables We discuss the baseline optical configuration for the Laser Interferometer Space Antenna (LISA) mission, in which the lasers are not free-running, but rather one of them is used as the main frequency reference generator (the {\it master}) and the remaining five as {\it slaves}, these being phase-locked to the master (the {\it master-slave configuration}). Under the condition that the frequency fluctuations due to the optical transponders can be made negligible with respect to the secondary LISA noise sources (mainly proof-mass and shot noises), we show that the entire space of interferometric combinations LISA can generate when operated with six independent lasers (the {\it one-way method}) can also be constructed with the {\it master-slave} system design. The corresponding hardware trade-off analysis for these two optical designs is presented, which indicates that the two sets of systems needed for implementing the {\it one-way method}, and the {\it master-slave configuration}, are essentially identical. Either operational mode could therefore be implemented without major implications on the hardware configuration. ----------------------------------------------------------------------------- Paper: hep-th/0304041 From: George Tsoupros Date (v1): Fri, 4 Apr 2003 19:53:02 GMT (26kb) Date (revised v2): Sun, 6 Apr 2003 15:59:36 GMT (26kb) Date (revised v3): Tue, 8 Apr 2003 19:20:04 GMT (26kb) Date (revised v4): Sun, 27 Apr 2003 20:04:39 GMT (27kb) Perturbative Evaluation of Interacting Scalar Fields on a Curved Manifold with Boundary Authors: George Tsoupros Comments: 25 pages, 1 figure. Minor elucidations in the Appendix regarding the cut-off $ N_0$ and in p.4 regarding the gravitational action. Certain reference-related ommission corrected. To appear in Classical and Quantum Gravity The effects of quantum corrections to a conformally invariant scalar field theory on a curved manifold of positive constant curvature with boundary are considered in the context of a renormalisation procedure. The renormalisation of the theory to second order in the scalar self-coupling pursued herein involves explicit calculations of up to third loop-order and reveals that, in addition to the renormalisation of the scalar self-coupling and scalar field, the removal of all divergences necessitates the introduction of conformally non-invariant counterterms proportional to $ R\Phi^2$ and $ K\Phi^2$ in the bare scalar action as well as counterterms proportional to $ RK^2$, $ R^2$ and $ RK$ in the gravitational action. The substantial backreaction effects and their relevance to the renormalisation procedure are analysed. ----------------------------------------------------------------------------- Paper: hep-th/0212333 From: Matt Visser Date (v1): Mon, 30 Dec 2002 04:52:45 GMT (8kb) Date (revised v2): Thu, 20 Feb 2003 02:50:13 GMT (9kb) On-brane data for braneworld stars Authors: Matt Visser (Victoria University of Wellington), David L. Wiltshire (University of Canterbury) Comments: 5 pages, RevTeX4, v2: Main algorithm and results substantially simplified, further discussion and references added Journal-ref: Phys.Rev. D67 (2003) 104004 Stellar structure in braneworlds is markedly different from that in ordinary general relativity. As an indispensable first step towards a more general analysis, we completely solve the ``on brane'' 4-dimensional Gauss and Codazzi equations for an arbitrary static spherically symmetric star in a Randall--Sundrum type II braneworld. We then indicate how this on-brane boundary data should be propagated into the bulk in order to determine the full 5-dimensional spacetime geometry. Finally, we demonstrate how this procedure can be generalized to solid objects such as planets. ----------------------------------------------------------------------------- Paper: gr-qc/0301003 From: Matt Visser Date (v1): Wed, 1 Jan 2003 19:44:42 GMT (8kb) Date (revised v2): Wed, 23 Apr 2003 02:14:32 GMT (8kb) Traversable wormholes with arbitrarily small energy condition violations Authors: Matt Visser (Victoria University of Wellington), Sayan Kar (Indian Institute of Technology), Naresh Dadhich (IUCAA, Pune) Comments: 4 pages, revtex4; V2: discussion refined and strengthened in view of referee comments, no changes in physics conclusions. To appear in Physical Review Letters Traversable wormholes necessarily require violations of the averaged null energy condition; this being the definition of ``exotic matter''. However, the theorems which guarantee the energy condition violation are remarkably silent when it comes to making quantitative statements regarding the ``total amount'' of energy condition violating matter in the spacetime. We develop a suitable measure for quantifying this notion, and demonstrate the existence of spacetime geometries containing traversable wormholes that are supported by arbitrarily small quantities of ``exotic matter''. ----------------------------------------------------------------------------- Paper: gr-qc/0305061 From: Matt Visser Date: Fri, 16 May 2003 00:44:56 GMT (10kb) Analogue models for FRW cosmologies Authors: Carlos Barcelo (University of Portsmouth), Stefano Liberati (University of Mayland), Matt Visser (Victoria University of Wellington) Comments: This essay was awarded an "honourable mention" in the 2003 essay competition of the Gravity Research Foundation. Uses revtex4; 6 pages in single-column format It is by now well known that various condensed matter systems may be used to mimic many of the kinematic aspects of general relativity, and in particular of curved-spacetime quantum field theory. In this essay we will take a look at what would be needed to mimic a cosmological spacetime -- to be precise a spatially flat FRW cosmology -- in one of these analogue models. In order to do this one needs to build and control suitable time dependent systems. We discuss here two quite different ways to achieve this goal. One might rely on an explosion, physically mimicking the big bang by an outflow of whatever medium is being used to carry the excitations of the analogue model, but this idea appears to encounter dynamical problems in practice. More subtly, one can avoid the need for any actual physical motion (and avoid the dynamical problems) by instead adjusting the propagation speed of the excitations of the analogue model. We shall focus on this more promising route and discuss its practicality. ----------------------------------------------------------------------------- Paper: gr-qc/0305109 From: Zhang Chengmin Date: Fri, 30 May 2003 04:53:29 GMT (7kb) Axial Torsion-Dirac spin Effect in Rotating Frame with Relativistic Factor Authors: C.M. Zhang Comments: 6 pages Journal-ref: Gen. Rel. Grav., 35(2003), No.8, 1465-1470 In the framework of spacetime with torsion and without curvature, the Dirac particle spin precession in the rotational system is studied. We write out the equivalent tetrad of rotating frame, in the polar coordinate system, through considering the relativistic factor, and the resultant equivalent metric is a flat Minkowski one. The obtained rotation-spin coupling formula can be applied to the high speed rotating case, which is consistent with the expectation. ******************************************************************************