Subject: ASGRG Newsletter #9 ****************************************************************************** AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION Electronic Newsletter -- #9, Autumn 2002 ****************************************************************************** Items for this newsletter should be emailed to the editor: asgrg *AT* hotmail *DOT* com The deadline for the next issue is 30 September, 2002. ****************************************************************************** CONTENTS: * 2002 AIP CONGRESS, Sydney, 8-11 July, 2002 * DEATH OF GEOFFREY OPAT * POSITION AT UNIVERSITY OF CANBERRA * MEMBERSHIP DETAILS ONLINE at http://www.physics.adelaide.edu.au/ASGRG/members.html * SUBSCRIPTIONS * FORTHCOMING MEETINGS * MEMBERS' ABSTRACTS at gr-qc, December 2001 - April 2002 ****************************************************************************** 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 Plenary Speaker for the ASGRG Interest Group will be Prof Barry Barish from CalTech, Director of LIGO. A total of 18 abstracts have been submitted to the AIP as part of the ASGRG Interest Group's contribution, and we have inherited 2 further talks from the collapse of the Astronomy Interest Group. The latest draft version of the ASGRG timetable (as of April 25) reads: Session 1, Monday 8 July, 1400-1530 Anderson: Self-similar evaporation of a rigidly rotating cosmic string loop. Scott: General properties of cosmological models with an isotropic singularity. Ericksson: A characterising feature of cosmological models with an isotropic singularity. Darabi: A gravitational conformal invariant model and coupling constants in 5D non-compact Kaluza-Klein models. Mititelu: Periodic solutions for the geodesic equations in the Reissner- Nordstrom metric. Session 2, Monday 8 July, 1700-1830 Ashley: The abstract boundary construction and singularity theorems. Beesham: Gravitational collapse of higher dimensional inhomogeneous dust. Flambaum: Do the fundamental constants of Nature vary with time and distance? Murphy: A variable fine structure constant? New results. Robinson: A variation of the spacetime geometry equation. Session 3, Wednesday 10 July, 1700-1900 (Jointly with AOP) Hanbury Brown retrospective. De Vine: Experimental demonstration of a variable reflectivity signal mirror for a Michelson interferometer GW detector. Brooks: Wavefront distortion in optical cavities for gravitational wave interferometers. Session 4, Thursday 11 July, 1430-1615 Barish (Plenary): The status and prospects for LIGO. McClelland: Progress report from ACIGA. Scott: Gravitational wave astronomy strategies and AIGO. Session 5, Thursday 11 July, 1645-1830 Cusack: Global correlations in physical environment monitors for gravitational wave detection. Searle: Spectral line removal for GW astronomy. Tobar: Michelson-Morley experiment using whispering spherical mode resonators. Slagmolen: Direct measurement of the thermal noise of a flexure suspension. Hollitt: A direct measurement of the spectrum of thermoelastic noise in sapphire. Ju Li: Vibration isolation and test mass suspension for laser interferometer gravitational wave detector. A full list of the AIP abstracts can be found at: http://www.aip.org.au/Congress2002/AbstractNew.htm A reminder that the deadline for early registration at the AIP Congress is the 16th of May 2002. ****************************************************************************** DEATH OF GEOFFREY OPAT It is with great sadness that we report the sudden death of Geoffrey Opat on March 7 of this year. Geoff was a member of the School of Physics at the University of Melbourne, and had been a member of the ASGRG since 1996. ****************************************************************************** POSITION AT UNIVERSITY OF CANBERRA A researcher with expertise in mathematical aspects of the Einstein equations is sought, to work on an ARC-supported project on "Energy in General Relativity" at the University of Canberra. The position is for 18 months, and would suit a recent PhD graduate in mathematics or theoretical physics with a background in geometry and analysis. Questions may be directed to bartnik@ise.canberra.edu.au. Application details are available at http://www.canberra.edu.au/recruitment/jobs/job-02-2024.html Please bring this notice to the attention of potential candidates. The formal closing date was 12th April 2002, but late applications will be considered. ****************************************************************************** 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. However, this year subscription details were posted out on April 21, for some unknown reason. This was definitely not initiated by ASGRG staff, and was possibly triggered by a robot or a hacker exploring the ASGRG website. In any case, all corrections mailed back to the asgrg website should now have been made to the subscription database. 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 2002 - June 2003 subscriptions are requested, if you wish to pay for July 2003 - June 2004 at the same time, it may simplify matters. ****************************************************************************** FORTHCOMING MEETINGS May 31-June 2, 2002: 5th Capra Ranch Meeting on Radiation Reaction in General Relativity State College, Pennsylvania, USA http://cgwp.gravity.psu.edu/capra5 June 10-11, 2002: BritGravII Queen Mary College, London, UK http://www.maths.qmul.ac.uk/~britgrav/ June 18-29, 2002: Cosmoseismology and Entropy Perturbations University of Portsmouth, Portsmouth, UK http://www.gravity.port.ac.uk/cosmoseismology June 22-July 3, 2002: XIV Petrov School: Recent Problems in Theoretical and Mathematical Physics Kazan, Tatarstan, Russia http://www.kcn.ru/petrov_school/2let_e.htm June 24-29, 2002: Numerical Relativity University of Minnesota, USA http://www.ima.umn.edu/nr/ June 26-29, 2002: 6th International Conference on the History of General Relativity Amsterdam, Netherlands http://www.science.uva.nl/~kox/HGR6.html 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 1-8, 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 12-15, 2002: XIth Oporto Meeting on Geometry, Topology and Physics Oporto, Portugal http://www.fc.up.pt/mp/actividades/om.html July 15-20, 2002: Black holes, Gravitational Waves and Cosmology Rome/Pescara, Italy http://www.icra.it/ICRA_Networkshops/INW10_RJR60/ July 15-30, 2002: Strings 2002 Cambridge, UK http://www.damtp.cam.ac.uk/strings2002/ July 19-24, 2002: 4th International LISA Symposium State College, Pennsylvania, USA http://cgwp.phys.psu.edu July 29-August 9, 2002: Xth Brazilian School of Cosmology and Gravitation Mangaratiba, Brazil http://www.cosmologia.cbpf.br 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 August 26-29, 2002: 12th Chinese Conference on Gravitation and Relativistic Astrophysics Yaan City, Sichuan Province, China September 5-6, 2002: Applications of Geometric Algebra Trinity College, Cambridge, UK http://www.clifford.org/~clf-alg/conferences.html September 6-10, 2002: 'Villa Mondragone' International School of Gravitation and Cosmology Villa Mondragone, Monte Porzio Catone (Rome), Italy http://www.sigrav.unige.it September 9-14, 2002: 2nd ISPM Workshop on Particles & Cosmology Tbilisi, Georgia http://www.rmi.acnet.ge/ispm November 15-18, 2002: Brane World 2 Kyoto, Japan November 26-29, 2002: 12th Japan GRG Workshop Tokyo, Japan December 9-13, 2002: XXIst Texas Symposium on Relativistic Astrophysics Florence, Italy http://www.arcetri.astro.it/%7Etexaflor/ 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, December 2001 - April 2002 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/0203015 From: Reg Cahill Date: Tue, 5 Mar 2002 04:41:44 GMT (48kb) Process Physics: From Quantum Foam to General Relativity Authors: Reginald T. Cahill Comments: 26 pages Latex, 1 separate eps file Progress in the new information-theoretic process physics is reported in which the link to the phenomenology of general relativity is made. In process physics the fundamental assumption is that reality is to be modelled as self-organising semantic (or internal or relational) information using a self-referentially limited neural network model. Previous progress in process physics included the demonstration that space and quantum physics are emergent and unified, with time a distinct non-geometric process, that quantum phenomena are caused by fractal topological defects embedded in and forming a growing three-dimensional fractal process-space, which is essentially a quantum foam. Other features of the emergent physics were: quantum field theory with emergent flavour and confined colour, 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. Here general relativity and the technical language of general covariance is seen not to be fundamental but a phenomenological construct, arising as an amalgam of two distinct phenomena: the `gravitational' characteristics of the emergent quantum foam for which `matter' acts as a sink, and the classical `spacetime' measurement protocol, but with the later violated by quantum measurement processes. Quantum gravity, as manifested in the emergent Quantum Homotopic Field Theory of the process-space or quantum foam, is logically prior to the emergence of the general relativity phenomenology, and cannot be derived from it. ----------------------------------------------------------------------------- Paper: hep-ph/0202168 From: Robert Brandenberger Date: Sun, 17 Feb 2002 11:23:54 GMT (11kb) Microwave Background Constraints on Decaying Defects Authors: Robert H. Brandenberger, Brandon Carter, Anne-Christine Davis Comments: 6 pages, 0 figures Embedded defects are predicted in a host of particle physics theories, in particular in the standard electroweak theory. They can be stabilized by interactions with the cosmological plasma, but will decay once the plasma falls out of equilibrium, emitting a substantial fraction of non-thermal photons. If the decay happens after a redshift of about $10^6$, these photons will give rise to spectral distortions of the Cosmic Microwave Background, which leads to strong constraints on the underlying particle physics theory. Such constraints apply to any model with decaying defects, and in particular to theories predicting decaying vortons, thereby leading to constraints stronger than the dark matter limit. ----------------------------------------------------------------------------- Paper: hep-ph/0201155 From: Robert Brandenberger Date (v1): Thu, 17 Jan 2002 14:40:12 GMT (31kb) Date (revised v2): Sun, 17 Feb 2002 13:28:08 GMT (32kb) Thermal Stabilisation of Superconducting Sigma Strings and their Drum Vortons Authors: Brandon Carter, Robert H. Brandenberger, Anne-Christine Davis Comments: 16 pages, 2 figures two references added We discuss various issues related to stabilized embedded strings in a thermal background. In particular, we demonstrate that such strings will generically become superconducting at moderately low temperatures, thus enhancing their stability. We then present a new class of defects - drum vortons - which arise when a small symmetry breaking term is added to the potential. We display these points within the context of the O(4) sigma model, relevant for hadrodynamics below the QCD scale. This model admits `embedded defects' (topological defect configurations of a simpler - in this case O(2) symmetric - model obtained by imposing an embedding constraint) that are unstable in the full model at zero temperature, but that can be stabilised (by electromagnetic coupling to photons) in a thermal gas at moderately high termperatures. It is shown here that below the embedded defect stabilisation threshold, there will still be stabilized cosmic string defects. However, they will not be of the symmetric embedded vortex type, but of an `asymmetric' vortex type, and are automatically superconducting. In the presence of weak symmetry breaking terms, such as arise naturally when using the O(4) model for hadrodynamics, the strings become the boundary of a new kind of cosmic sigma membrane, with tension given by the pion mass. The string current would then make it possible for a loop to attain a (classically) stable equilibrium state that differs from an ``ordinary'' vorton state by the presence of a sigma membrane stretched across it in a drum like configuration. Such defects will however be entirely destabilised if the symmetry breaking is too strong, as is found to be the case -- due to the rather large value of the pion mass -- in the hadronic application of the O(4) sigma model. ----------------------------------------------------------------------------- Paper: gr-qc/0201002 From: Dr Simon Brian Davis Date (v1): Mon, 31 Dec 2001 21:57:05 GMT (10kb) Date (revised v2): Wed, 13 Feb 2002 17:41:21 GMT (11kb) The quantum theory of a quadratic gravity action for heterotic strings Authors: Simon Davis, Hugh Luckock Comments: 12 pages. Renormalizability properties of the action are clarified and a third-order differential equation for the wave function $\Psi$ with a dependence on the potential $V(\Phi)$ is included Report-no: University of Sydney Report 2001-17 The wave function for the quadratic gravity theory derived from the heterotic string effective action is deduced to first order in ${{e^{-\Phi}}\over {g_4^2}}$ by solving a perturbed second-order Wheeler-DeWitt equation, assuming that the potential is slowly varying with respect to $\Phi$. Predictions for inflation based on the solution to the second-order Wheeler-DeWitt equation continue to hold for this theory. It is shown how formal expressions for the average paths in minisuperspace $\{< a(t) >, < \Phi(t)> \}$ determine the shifts from the classical solutions to $a_{cl}(t)$ and $\Phi_{cl}(t)$, which occur only at third order in the expansion of the integrals representing the expectation values. ----------------------------------------------------------------------------- Paper: gr-qc/0112051 From: Hossein Farajollahi Date (v1): Thu, 20 Dec 2001 06:10:37 GMT (15kb) Date (revised v2): Fri, 21 Dec 2001 01:49:16 GMT (15kb) Dirac observables and the phase space of general relativity Authors: Hossein Farajollahi, Hugh Luckock Comments: Latex,18 pages,no figures In the canonical approach to general relativity it is customary to parametrize the phase space by initial data on spacelike hypersurfaces. However, if one seeks a theory dealing with observations that can be made by a single localized observer, it is natural to use a different description of the phase space. This results in a different set of Dirac observables from that appearing in the conventional formulation. It also suggests a possible solution to the problem of time, which has been one of the obstacles to the development of a satisfactory quantum theory of gravity. ----------------------------------------------------------------------------- Paper: gr-qc/0203094 From: Marie-Noelle Celerier Date: Tue, 26 Mar 2002 16:16:26 GMT (19kb) Timelike and null focusing singularities in spherical symmetry: a solution to the cosmological horizon problem and a challenge to the cosmic censorship hypothesis Authors: Marie-Noelle Celerier (Observatoire de Paris-Meudon), Peter Szekeres (University of Adelaide) Comments: 26 pages, 2 figures, LaTeX file. Submitted to Phys. Rev. D Extending the study of spherically symmetric metrics satisfying the dominant energy condition and exhibiting singularities of power-law type initiated in SI93, we identify two classes of peculiar interest: focusing timelike singularity solutions with the stress-energy tensor of a radiative perfect fluid (equation of state: $p={1\over 3} \rho$) and a set of null singularity classes verifying identical properties. We consider two important applications of these results: to cosmology, as regards the possibility of solving the horizon problem with no need to resort to any inflationary scenario, and to the Strong Cosmic Censorship Hypothesis to which we propose a class of physically consistent counter-examples. ----------------------------------------------------------------------------- Paper: gr-qc/0204062 From: visser@tui.wustl.edu (Matt Visser) Date: Fri, 19 Apr 2002 02:33:15 GMT (19kb) Sakharov's induced gravity: a modern perspective Authors: Matt Visser (Washington University in Saint Louis) Comments: mpla.sty; 17 pages. Contribution to the ``First IUCAA Meeting on the Interface of Gravitational and Quantum Realms'', held in Pune in December 2001. To appear in Modern Physics Letters A Sakharov's 1967 notion of ``induced gravity'' is currently enjoying a significant resurgence. The basic idea, originally presented in a very brief 3-page paper with a total of 4 formulas, is that gravity is not ``fundamental'' in the sense of particle physics. Instead it was argued that gravity (general relativity) emerges from quantum field theory in roughly the same sense that hydrodynamics or continuum elasticity theory emerges from molecular physics. In this article I will translate the key ideas into modern language, and explain the various versions of Sakharov's idea currently on the market. ----------------------------------------------------------------------------- Paper: gr-qc/0204022 From: visser@tui.wustl.edu (Matt Visser) Date (v1): Fri, 5 Apr 2002 02:20:47 GMT (24kb) Date (revised v2): Wed, 17 Apr 2002 19:49:54 GMT (24kb) The quantum physics of chronology protection Authors: Matt Visser (Washington University in Saint Louis) Comments: CUP style: uses cmmp.cls; 18 pages; contribution to "The future of theoretical physics and cosmology", conference in honour of Professor Stephen Hawking on the occasion of his 60'th birthday. V2: Some references added This is a brief survey of the current status of Stephen Hawking's ``chronology protection conjecture''. That is: ``Why does nature abhor a time machine?'' I'll discuss a few examples of spacetimes containing ``time machines'' (closed causal curves), the sorts of peculiarities that arise, and the reactions of the physics community. While pointing out other possibilities, this article concentrates on the possibility of ``chronology protection''. As Stephen puts it: ``It seems that there is a Chronology Protection Agency which prevents the appearance of closed timelike curves and so makes the universe safe for historians.'' ----------------------------------------------------------------------------- Paper: gr-qc/0204017 From: visser@tui.wustl.edu (Matt Visser) Date: Thu, 4 Apr 2002 02:25:15 GMT (19kb) Bi-refringence versus bi-metricity Authors: Matt Visser (Washington University in Saint Louis), Carlos Barcelo (Portsmouth University), Stefano Liberati (University of Maryland) Comments: Revtex 4; 10 pages in double-column format; contribution to the Festschrift in honour of Professor Mario Novello In this article we carefully distinguish the notion of bi-refringence (a polarization-dependent doubling in photon propagation speeds) from that of bi-metricity (where the two photon polarizations ``see'' two distinct metrics). We emphasise that these notions are logically distinct, though there are special symmetries in ordinary (3+1)-dimensional nonlinear electrodynamics which imply the stronger condition of bi-metricity. To illustrate this phenomenon we investigate a generalized version of (3+1)-dimensional nonlinear electrodynamics, which permits the inclusion of arbitrary inhomogeneities and background fields. [For example dielectrics (a la Gordon), conductors (a la Casimir), and gravitational fields (a la Landau--Lifshitz).] It is easy to demonstrate that the generalized theory is bi-refringent: In (3+1) dimensions the Fresnel equation, the relationship between frequency and wavenumber, is always quartic. It is somewhat harder to show that in some cases (eg, ordinary nonlinear electrodynamics) the quartic factorizes into two quadratics thus providing a bi-metric theory. Sometimes the quartic is a perfect square, implying a single unique effective metric. We investigate the generality of this factorization process. ----------------------------------------------------------------------------- Paper: gr-qc/0203061 From: Carlos O. Lousto Date: Mon, 18 Mar 2002 22:02:14 GMT (12kb) Reconstruction of Black Hole Metric Perturbations from Weyl Curvature Authors: Carlos O. Lousto (UT Brownsville), Bernard F. Whiting (U Florida) Comments: 6 Pages, Revtex4 Report-no: UTBRG-2001-03 Perturbation theory of rotating black holes is usually described in terms of Weyl scalars $\psi_4$ and $\psi_0$, which each satisfy Teukolsky's complex master wave equation and respectively represent outgoing and ingoing radiation. On the other hand metric perturbations of a Kerr hole can be described in terms of (Hertz-like) potentials $\Psi$ in outgoing or ingoing {\it radiation gauges}. In this paper we relate these potentials to what one actually computes in perturbation theory, i.e $\psi_4$ and $\psi_0$. We explicitly construct these relations in the nonrotating limit, preparatory to devising a corresponding approach for building up the perturbed spacetime of a rotating black hole. We discuss the application of our procedure to second order perturbation theory and to the study of radiation reaction effects for a particle orbiting a massive black hole. ----------------------------------------------------------------------------- Paper: gr-qc/0202086 From: Steven Detweiler Date (v1): Mon, 25 Feb 2002 20:34:29 GMT (8kb) Date (revised v2): Thu, 7 Mar 2002 21:13:44 GMT (9kb) Self-force via a Green's function decomposition Authors: Steven Detweiler, Bernard F. Whiting Comments: 4 pages; new paragraph on gauge condition; corrected reference; added acknowledgment; minor text changes The gravitational field of a particle of small mass \mu moving through curved spacetime is naturally decomposed into two parts each of which satisfies the perturbed Einstein equations through O(\mu). One part is an inhomogeneous field which, near the particle, looks like the \mu/r field distorted by the local Riemann tensor; it does not depend on the behavior of the source in either the infinite past or future. The other part is a homogeneous field and includes the ``tail term''; it completely determines the self force effects of the particle interacting with its own gravitational field, including radiation reaction. Self force effects for scalar, electromagnetic and gravitational fields are all described in this manner. -----------------------------------------------------------------------------