Subject: ASGRG Newsletter #11
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AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION
Electronic Newsletter -- #11, Autumn 2003
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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.
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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
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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.
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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/
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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''.
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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.
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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.
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