Items for this newsletter should be emailed to the editor: asgrg *AT* hotmail *DOT* com

- WORKSHOP IN CONJUNCTION WITH AIP'2000 - CALL FOR PAPERS - DEADLINE FOR ABSTRACTS EXTENDED - PLEASE SEND THEM IN NOW
- AMALDI4, Perth, 8-13 July 2001
- SUBSCRIPTIONS
- LECTURESHIPS IN PHYSICS AND ASTRONOMY - University of Canterbury (closing date: 20/10/2000)
- Date for ACGRG3, Perth, will be: July, 2001.
- MEMBERS' ABSTRACTS AT gr-qc January - July, 2000

Not everyone who had promised to give a talk submitted an abstract. Thus the deadline is being extended to 7 September. If you would like to speak PLEASE SUBMIT YOUR ABSTRACT as soon as possible, following the instructions in the last newsletter, which are online at

http://www2.phys.canterbury.ac.nz/ASGRG/news/news5.html

or (in PDF format) at

http://www.physics.adelaide.edu.au/aip-sa/aip2000/AIP2000.pdf

http://www.gravity.uwa.edu.au/amaldi/amaldi.htm

Details for ACGRG3 to be held at approximately similar dates are being finalised, and will be posted with the next newsletter.

A reminder for anyone who did not pay their subscriptions for July 1999 - June 2000, please do so promptly.

You can do this by following instructions at:

http://www2.phys.canterbury.ac.nz/ASGRG/subsform.html

Subscriptions for the current financial year (July 2000 - June 2001) will be requested once we have clarified our GST status.

LECTURESHIPS IN PHYSICS AND ASTRONOMY - University of Canterbury (closing date: 20/10/2000)

MEMBERS' ABSTRACTS AT gr-qc January - July, 2000

We list here all 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/0003044 From: abeesham <abeesham@pan.uzulu.ac.za> Date: Fri, 10 Mar 2000 08:05:35 GMT (7kb) Title: Naked Singularities in the Charged Vaidya-deSitter Spacetime Authors: A. Beesham, S. G. Ghosh Comments: 8 pages, latex, no figures We study the occurrence of naked singularities in the spherically symmetric collapse of a charged null fluid in an expanding deSitter background - a piece of charged Vaidya-deSitter spacetime. The necessary conditions for the formation of a naked singularity are found. The results for the uncharged solutions can be recovered from our analysis. \\ ( http://arXiv.org/abs/gr-qc/0003044 , 7kb) ------------------------------------------------------------------------------ \\ Paper: gr-qc/0003109 From: abeesham <abeesham@pan.uzulu.ac.za> Date: Thu, 30 Mar 2000 06:39:50 GMT (10kb) Title: Naked Singularities in Higher Dimensional Tolman-type Spacetime Authors: S G Ghosh, A Beesham Comments: 10 pages, latex, no figures Gravitaional collapse of an inhomogeneous dust cloud described by a higher dimensional Tolman type spacetime is studied. The necessary conditions for the formation of a naked singularity or a black hole is obtained. \\ ( http://arXiv.org/abs/gr-qc/0003109 , 10kb) ------------------------------------------------------------------------------ \\ Paper: gr-qc/0004019 From: Alan Barnes <barnesa@sun.aston.ac.uk> Date: Thu, 6 Apr 2000 15:06:57 GMT (5kb) Title: A comment on a paper by Carot et al Authors: Alan Barnes (Aston University) Comments: 6 pages, TeX Journal-ref: Class.Quant.Grav. 17 (2000) 2605 In a recent paper Carot et al. considered carefully the definition of cylindrical symmetry as a specialisation of the case of axial symmetry. One of their propositions states that if there is a second Killing vector, which together with the one generating the axial symmetry, forms the basis of a two-dimensional Lie algebra, then the two Killing vectors must commute, thus generating an Abelian group. In this comment a similar result, valid under considerably weaker assumptions, is recalled: any two-dimensional Lie transformation group which contains a one-dimensional subgroup whose orbits are circles, must be Abelian. The method used to prove this result is extended to apply to three-dimensional Lie transformation groups. It is shown that the existence of a one-dimensional subgroup with closed orbits restricts the Bianchi type of the associated Lie algebra to be I (Abelian), II, III, VII_0, VIII or IX. The relationship between the present approach and that of the original paper is discussed. \\ ( http://arXiv.org/abs/gr-qc/0004019 , 5kb) ------------------------------------------------------------------------------ \\ Paper: gr-qc/0004033 From: Alfonso F. Agnew <aagnew@golem.math.smu.edu> Date: Tue, 11 Apr 2000 20:59:54 GMT (18kb) Title: Distributional Modes for Scalar Field Quantization Authors: Alfonso F. Agnew, Tevian Dray Comments: 15 pages, RevTeX Report-no: MATH-SMU-00-06 We propose a mode-sum formalism for the quantization of the scalar field based on distributional modes, which are naturally associated with a slight modification of the standard plane-wave modes. We show that this formalism leads to the standard Rindler temperature result, and that these modes can be canonically defined on any Cauchy surface. \\ ( http://arXiv.org/abs/gr-qc/0004033 , 18kb) ------------------------------------------------------------------------------ \\ Paper: astro-ph/0004138 From: Cindy Ng <cng@physics.adelaide.edu.au> Date (v1): Tue, 11 Apr 2000 07:53:19 GMT (547kb) Date (revised v2): Wed, 12 Apr 2000 01:22:35 GMT (547kb) Title: Properties of cosmologies with dynamical pseudo Nambu-Goldstone bosons Authors: S.C.C. Ng and D.L. Wiltshire Comments: 21 pages, RevTeX, 13 figures, epsf Report-no: ADP-00-11/M91 We study observational constraints on cosmological models with a quintessence field in the form of a dynamical pseudo Nambu-Goldstone boson. After reviewing the properties of the solutions, from a dynamical systems phase space analysis, we consider the constraints on parameter values imposed by luminosity distances from the 60 Type Ia supernovae published by Perlmutter et al., and also from gravitational lensing statistics of distant quasars. In the case of the Type Ia supernovae we explicitly allow for the possibility of evolution of the peak luminosities of the supernovae sources, using simple empirical models which have been recently discussed in the literature. We find weak evidence to suggest that the models with supernovae evolution fit the data better in the context of the quintessence models in question. If source evolution is a reality then the greatest challenge facing these models is the tension between current value of the expansion age, H_0 t_0, and the fraction of the critical energy density, Omega_{phi0}, corresponding to the scalar field. Nonetheless there are ranges of the free parameters which fit all available cosmological data. \\ ( http://arXiv.org/abs/astro-ph/0004138 , 547kb) ------------------------------------------------------------------------------ \\ Paper: astro-ph/0004196 From: Cindy Ng <cng@physics.adelaide.edu.au> Date: Fri, 14 Apr 2000 06:36:05 GMT Title: Observational constraints upon quintessence models arising from double exponential potentials Authors: S.C.C. Ng Comments: 7 pages, RevTeX, 9 figures, epsf Report-no: ADP-00-19/M92 We study observational constraints on cosmological models with a quintessence arises from moduli fields. The scalar field potential is given by a double exponential potential V=V_0 exp(-A e^{sqrt{2} kappa phi}). After reviewing the properties of the solutions, from a dynamical systems phase space analysis, we consider the constraints on parameter values imposed by luminosity distances from the 60 Type IA supernovae published by Perlmutter et al., and also from gravitational lensing statistics of distant quasars. We also update the constraints on models with a single exponential potential V=V_0 e^{-lambda kappa phi}. \\ ( http://arXiv.org/abs/astro-ph/0004196 , 70kb) ------------------------------------------------------------------------------ \\ Paper: gr-qc/0005113 From: Warner A. Miller <wam@t6-serv.lanl.gov> Date (v1): Thu, 25 May 2000 03:15:32 GMT (493kb) Date (revised v2): Mon, 8 Jan 2001 20:17:17 GMT (70kb) Title: Constant Crunch Coordinates for Black Hole Simulations Authors: Adrian P. Gentle, Daniel E. Holz, Arkady Kheyfets, Pablo Laguna, Warner A. Miller, Deirdre M. Shoemaker Comments: 14 pages, 9 figures. Formatted using Revtex4. To appear Phys. Rev. D 2001, Added numerical results, updated references and revised figures We reinvestigate the utility of time-independent constant mean curvature foliations for the numerical simulation of a single spherically-symmetric black hole. Each spacelike hypersurface of such a foliation is endowed with the same constant value of the trace of the extrinsic curvature tensor, $K$. Of the three families of $K$-constant surfaces possible (classified according to their asymptotic behaviors), we single out a sub-family of singularity-avoiding surfaces that may be particularly useful, and provide an analytic expression for the closest approach such surfaces make to the singularity. We then utilize a non-zero shift to yield families of $K$-constant surfaces which (1) avoid the black hole singularity, and thus the need to excise the singularity, (2) are asymptotically null, aiding in gravity wave extraction, (3) cover the physically relevant part of the spacetime, (4) are well behaved (regular) across the horizon, and (5) are static under evolution, and therefore have no ``grid stretching/sucking'' pathologies. Preliminary numerical runs demonstrate that we can stably evolve a single spherically-symmetric static black hole using this foliation. We wish to emphasize that this coordinatization produces $K$-constant surfaces for a single black hole spacetime that are regular, static and stable throughout their evolution. \\ ( http://arXiv.org/abs/gr-qc/0005113 , 70kb) ------------------------------------------------------------------------------ \\ Paper: gr-qc/0006017 From: Adrian P. Gentle <adrian@regge.lanl.gov> Date: Mon, 5 Jun 2000 23:05:23 GMT (36kb) Title: On the convergence of Regge calculus to general relativity Authors: Leo C. Brewin and Adrian P. Gentle Comments: 9 pages, 4 EPS figures Report-no: LAUR-00-2300 \\ Motivated by a recent study casting doubt on the correspondence between Regge calculus and general relativity in the continuum limit, we explore a mechanism by which the simplicial solutions can converge whilst the residual of the Regge equations evaluated on the continuum solutions does not. By directly constructing simplicial solutions for the Kasner cosmology we show that the oscillatory behaviour of the discrepancy between the Einstein and Regge solutions reconciles the apparent conflict between the results of Brewin and those of previous studies. We conclude that solutions of Regge calculus are, in general, expected to be second order accurate approximations to the corresponding continuum solutions. \\ ( http://arXiv.org/abs/gr-qc/0006017 , 36kb) ------------------------------------------------------------------------------ \\ Paper: gr-qc/0007061 From: Tamath Rainsford <eguest@physics.adelaide.edu.au> Date: Sun, 23 Jul 2000 15:28:48 GMT (20kb) Title: Anisotropic Homogeneous Cosmologies in the Post-Newtonian Approximation Author: Tamath Rainsford (University of Adelaide) Comments: 22 pages, LATEX In this paper we explore how far the post-Newtonian theory goes in overcoming the difficulties associated with anisotropic homogeneous cosmologies in the Newtonian approximation. It will be shown that, unlike in the Newtonian case, the cosmological equations of the post-Newtonian approximation are much more in the spirit of general relativity with regard to the nine Bianchi types and issues of singularities. The situations of vanishing rotation and vanishing shear are treated separately. The homogeneous Bianchi I model is considered as an example of a rotation-free cosmology with anisotropy. It is found in the Newtonian approximation that there are arbitrary functions that need to be given for all time if the initial value problem is to be well-posed, while in the post-Newtonian case there is no such need. For the general case of a perfect fluid only the post-Newtonian theory can satisfactorily describe the effects of pressure. This is in accordance with findings in an earlier paper where the post-Newtonian approximation was applied to homogeneous cosmologies. For a shear-free anisotropic homogeneous cosmology the Newtonian theory of Heckmann and Sch\"ucking is explored. Comparisons with its relativistic and post-Newtonian counterparts are made. In the Newtonian theory solutions exist to which there are no analogues in general relativity. The post-Newtonian approximation may provide a way out. \\ ( http://arXiv.org/abs/gr-qc/0007061 , 20kb) ------------------------------------------------------------------------------