Electronic Newsletter -- #6 Spring 2000

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



As previously notified the ASGRG will be holding experimental and theoretical workshops in conjunction with the AIP'2000 Congress, Adelaide, 10-15, December, 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

or (in PDF format) at


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:

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 <>
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.
\\ ( ,  7kb)
Paper: gr-qc/0003109
From: abeesham <>
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.
\\ ( ,  10kb)
Paper: gr-qc/0004019
From: Alan Barnes <>
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.
\\ ( ,  5kb)
Paper: gr-qc/0004033
From: Alfonso F. Agnew <>
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.
\\ ( ,  18kb)
Paper: astro-ph/0004138
From: Cindy Ng <>
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
\\ ( ,  547kb)
Paper: astro-ph/0004196
From: Cindy Ng <>
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}.
\\ ( ,  70kb)
Paper: gr-qc/0005113
From: Warner A. Miller <>
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.

\\ ( , 70kb)
Paper: gr-qc/0006017
From: Adrian P. Gentle <>
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.
\\ ( ,  36kb)
Paper: gr-qc/0007061
From: Tamath Rainsford <>
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.
\\ ( ,  20kb)