Subject: ASGRG Newsletter #8
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AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION
Electronic Newsletter -- #8, Spring 2001
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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 March, 2002.
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CONTENTS:
* 2002 AIP CONGRESS, Sydney, 8-11 July, 2002
* REPORT ON ACGRG3, Perth, 11-13 July, 2001
* MINUTES OF BIENNIAL GENERAL MEETING, Perth, 11 July, 2001
* DEATH OF NOEL DOUGHTY
* MEMBERSHIP DETAILS ONLINE at
http://www.physics.adelaide.edu.au/ASGRG/members.html
* SUBSCRIPTIONS
* FORTHCOMING MEETINGS
* MEMBERS' ABSTRACTS at gr-qc, March 2001 – November 2001
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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 ASGRG
Interest Group has nominated Prof Barry Barish from CalTech, Director
of LIGO, as our Plenary Speaker.
We are now calling for papers to be presented as part of the ASGRG
Interest Group's contribution. The Call for Papers appeared in the
November edition of the Australian Physicist, and abstracts should
be submitted through the Congress web site, which is at
http://www.aip.org.au/Congress2002
The closing date for submission of abstracts is the 15th of February
2002. See the web site for further information on the Congress.
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REPORT ON ACGRG3, Perth, July 11-13 2001
ACGRG3, the third in the roughly biennial sequence of conferences so far
organized by the Society, was held at the University of Western Australia
from July 11 to July 13 this year, in tandem with the 4th Edoardo Amaldi
Conference on Gravitational Waves.
At total of 18 presentations were given over the three days of ACGRG3,
including invited talks from Matt Visser ("Analog Gravity"), Hugh Luckock
("Dirac Observables and the Phase Space of General Relativity"), Neil
Cornish ("Chaos and Gravitational Waves"), Adrian Gentle ("Regge
Calculus") and Peter Szekeres ("The Hubble Index"). Special mention should
also be given to Bernard Whiting, who at extremely short notice contributed a
talk on algebraically special perturbations in gravity wave research to fill
a gap caused by a late withdrawal.
The more technical presentations included three talks on gravito-
electrodynamics from the Monash group, talks on the abstract boundary and
GRworkbench from the ANU group, plus talks on the effective action of a
self-interacting scalar field, axisymmetric vacuum gravitation, quintessence,
process physics, Gowdy symmetric spacetimes and cosmic strings.
The Conference Excursion on July 12 involved a quick lunch and walk
around the Yanchep National Park north of Perth, followed by an
afternoon exploring the Australian International Gravitational Observatory
(AIGO), which included an opportunity to sample some of the wares of
the local wineries. The Conference Banquet, a spit roast dinner, was held
in an enormous marquee in a paddock just outside the town of Gingin.
The last day of ACGRG3 was marked by a dinner in honour of Peter
Szekeres at a charming French restaurant on the Stirling Highway.
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MINUTES OF THE 3RD BIENNIAL GENERAL MEETING OF THE ASGRG
held at the University of Western Australia, Perth, 11 July, 2001
The meeting opened at 5.40 p.m.
Apologies: David Blair
1. The minutes of the 2nd Biennial General Meeting, held at the University
of Sydney, 8 July 1998, were presented to the meeting. Tony Lun moved
that the minutes be accepted, and Peter Szekeres seconded. The motion was
approved.
2. President's Report: David McClelland informed the meeting that the
ASGRG had been given Cognate Society Status with the Australian
Institute of Physics at the beginning of 2000. He urged all ASGRG
members to join the AIP (the fee is $150). He also raised the possibility
that the ASGRG should become a member of FASTS, but no decision was
made on this.
David briefly mentioned the most recent activity of the Society,
namely the ASGRG workshop attached to the AIP Congress in Adelaide
in December 2000. The ASGRG partly sponsored the attendance of John
Barrow at AIP 2000 as a plenary invited speaker. On another front, three
ASGRG committee members attended the first Science Meets Parliament
Day, but all declined to attend the second.
David reported that the Society's numbers have remained roughly
constant since 1998, although relativity research remains in a dire state
in Australia. David Wiltshire and Peter Szekeres were leaving Adelaide
University without replacement, while Adrian Gentle had moved to Los
Alamos and Malcolm Anderson to Brunei. No funding was forthcoming
for the national gravity wave facility, and no action had yet been taken on
assigning a separate ARC Category Code to general relativity, gravitation
and cosmology (the ARC programme manager responsible for this is Laurie
Cram).
Finally, David suggested that the ASGRG Newsletter continue to
be published on a half-yearly basis.
Tony Lun added that the ASGRG had been commended by the AIP
for bidding for the 17th International Conference of the ISGRG (GR17).
3. Treasurer's Report: Susan Scott reported that the Society's funds had
increased from $3,398 on 16 June 1998 to $11,393 on 21 June 2001,
although the latter figure included a debt of about $1000 to the ANU
Department of Physics. This striking increase in the Society's funds was
due almost entirely to the accumulation of membership fees. Currently
the ASGRG had 21 Life Members (who had each paid $250), 20 Ordinary
Members (each paying $30 a year) and 4 Retired, 15 Student and 3 Unwaged
Members (each paying $15 a year).
According to Sue, ACGRG2 (Sydney, 1998) had returned a profit of
$1488, while she expected ACGRG3 (Perth, 2001) to either lose money or
break even. The outstanding costs of ACGRG3 included $1000 to the UWA
Adminstrator, $25 per person for the conference excursion, and $450 for the
five tea breaks. In addition, the ASGRG contributed $800 of the $3000
sponsorship extended to John Barrow for his attendance at AIP 2000.
4. Auditor's Report: A letter from the Auditor, Hugh Luckock, stating that
he was satisfied with the Society's accounts was tabled before the meeting
and accepted. The suggestion was made that a life membership lottery
should be offered to anyone who joins the ASGRG in the next two years,
but no decision was made on this.
5. Appointment of Auditor for the next session: John Schutz agreed to
become the next Auditor of the Society's accounts.
6. Election of officers: The following people were elected officers of
the ASGRG Committee by acclamation (the mover and seconder are
shown in brackets):
President: David McClelland (Searle, Shaddock)
Treasurer: Susan Scott (McClelland, Shaddock)
Secretary: Malcolm Anderson (Wiltshire, Whiting)
Officer: David Wiltshire (Charlton, Luckock)
Officer: Peter Szekeres (Wiltshire, Whiting)
7. Invited Speaker for AIP 2002 Congress, July 2002: The meeting
decided to ask Barry Barish, the Director of the LIGO Project, to
become the ASGRG Interest Group's Invited Speaker at the AIP
2002 Congress in July 2002, with Kip Thorne as a second choice.
8. Date and venue for ACGRG4: The meeting decided (tentatively) that
ACGRG4 would be held at Monash University in December 2003 or
January 2004.
9. Co-option of further committee members: In view of the decisions
reported in items 7 and 8 above, the meeting moved to co-opt Tony Lun
of Monash University and (in absentia) John Steele of UNSW as
extraordinary members of the ASGRG Committee.
10. Bid for GR17, Cairns, 2004: Susan Scott entertained the meeting with
a preview of the bid for GR17 that the ASGRG was about to make at the
forthcoming GR16 meeting in Durban. The proposed venue was the Cairns
Convention Centre, and the proposed date the first week of July 2004. Sue
anticipated that between 500 and 700 delegates would attend. With a
registration fee of around $600 per delegate, the weekly hire cost of
$34,000 for the Convention Centre would be more than adequately covered.
[Unfortunately, the ASGRG bid lost out at Durban, and GR17 went to Dublin.]
11. Other business: Peter Szekeres was appointed editor of the proceedings
of ACGRG3, which are to appear in General Relativity and Gravitation. The
deadline for manuscripts was nominated as the end of October [but has since
been changed to the end of November].
The meeting closed at 7 p.m.
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DEATH OF NOEL DOUGHTY
It is with great sadness that we have to report the tragic death of Noel A
Doughty, aged 62, who recently took early retirement from the Department
of Physics and Astronomy at the University of Canterbury, Christchurch,
New Zealand.
Noel is well known for his textbook "Lagrangian Interaction – An Introduction
to Relativistic Symmetry in Electrodynamics and Gravitation" and is fondly
remembered by many former students scattered around the world, who were
inspired to undertake careers in theoretical physics by Noel's enthusiasm,
his friendly help as a supervisor, and his unique and original approach to
his lectures. He will be deeply missed.
David Wiltshire
Amanda Peet
Richard Easther
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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 new version of the membership script programs will 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
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
2001 – June 2002 subscriptions are requested, if you wish to pay for July
2002 – June 2003 at the same time, it may simplify matters.
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FORTHCOMING MEETINGS
June 10-11, 2002: BritGravII
Queen Mary College, London, UK
June 22-July 3, 2002: XIV Petrov School: Recent Problems in Theoretical
and Mathematical Physics
Kazan, Tatarstan, Russia
http://www.kcn.ru/petrov_school
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 1-10, 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 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
November 15-18, 2002: Brane World 2
Kyoto, Japan
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
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MEMBERS' ABSTRACTS at gr-qc, March 2001 - November 2001
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/0110028
From: Alan Barnes
Date: Thu, 4 Oct 2001 21:15:02 GMT (12kb)
Title: Ricci Collineations in Friedmann-Robertson-Walker Spacetimes
Authors: Ugur Camci, Alan Barnes
Comments: 14 pages, plain TeX, no figures
Ricci collineations and Ricci inheritance collineations of Friedmann-
Robertson-Walker spacetimes are considered. When the Ricci tensor is
non-degenerate, it is shown that the spacetime always admits a fifteen
parameter group of Ricci inheritance collineations; this is the maximal
possible dimension for spacetime manifolds. The general form of the
vector generating the symmetry is exhibited. It is also shown, in the
generic case, that the group of Ricci collineations is six-dimensional
and coincides with the isometry group. In special cases the spacetime
may admit either one or four proper Ricci collineations in addition to
the six isometries. These special cases are classified and the general
form of the vector fields generating the Ricci collineations is exhibited.
When the Ricci tensor is degenerate, the groups of Ricci inheritance
collineations and Ricci collineations are infinite-dimensional. General
forms for the generating vectors are obtained. Similar results are
obtained for matter collineations and matter inheritance collineations.
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Paper: gr-qc/0109037
From: Alan Barnes
Date: Tue, 11 Sep 2001 14:02:12 GMT (6kb)
Title: On the Symmetries of the Edgar-Ludwig Metric
Authors: Alan Barnes
Comments: Plain TeX, 7 pages, No figures
The conformal Killing equations for the most general (non-plane wave)
conformally flat pure radiation field are solved to find the conformal
Killing vectors. As expected fifteen independent conformal Killing
vectors exist, but in general the metric admits no Killing or homothetic
vectors. However for certain special cases a one-dimensional group of
homotheties or motions may exist and in one very special case,
overlooked by previous investigators, a two-dimensional homethety
group exists. No higher dimensional groups of motions or homotheties
are admitted by these metrics.
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Paper: gr-qc/0109036
From: Alan Barnes
Date: Tue, 11 Sep 2001 13:43:22 GMT (9kb)
Title: Some Restrictions on Symmetry Groups of Axially Symmetric Spacetimes
Authors: Alan Barnes
Comments: Plain TeX, 11 pages. No figures
Lie transformation groups containing a one-dimensional subgroup
acting cyclically on a manifold are considered. The structure of the
group is found to be considerably restricted by the existence of a one-
dimensional subgroup whose orbits are circles. The results proved do
not depend on the dimension of the manifold nor on the existence of a
metric, but merely on the fact that the Lie group acts globally on the
manifold. Firstly some results for the general case of an $m+1$-
dimensional Lie group are derived: those commutators of the associated
Lie algebra involving the generator of the cyclic subgroup, $X_0$ say,
are severely restricted and, in a suitably chosen basis, take a simple
form. The Jacobi identities involving $X_0$ are then applied to show
there are further restrictions on the structure of the Lie algebra. All Lie
algebras of dimensions 2 and 3 compatible with cyclic symmetry are
obtained. In the two-dimensional case the group must be Abelian. For
the three-dimensional case, the Bianchi type of the Lie algebra must be
I, II, III, VII$_0$, VIII or IX and furthermore in all cases the vector
$X_0$ forms part of a basis in which the algebra takes its canonical
form. Finally four-dimensional Lie algebras compatible with cyclic
symmetry are considered and the results are related to the Petrov-
Kruchkovich classification of all four-dimensional Lie algebras.
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Paper: gr-qc/0111075
From: Zhang Chengmin
Date: Thu, 22 Nov 2001 10:23:14 GMT (8kb)
Title: Rotation intrinsic spin coupling--the parallelism description
Authors: C.M. Zhang, A. Beesham
Comments: 10 pages, no figure
For the Dirac particle in the rotational system, the rotation induced
inertia effect is analogously treated as the modification of the "spin
connection" on the Dirac equation in the flat spacetime, which is
determined by the equivalent tetrad. From the point of view of
parallelism description of spacetime, the obtained torsion axial-vector
is just the rotational angular velocity, which is included in the "spin
connection". Furthermore the axial-vector spin coupling induced spin
precession is just the rotation-spin(1/2) interaction predicted by
Mashhoon. Our derivation treatment is straightforward and simplified
in the geometrical meaning and physical conception, however the
obtained conclusions are consistent with that of the other previous
work.
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Paper: gr-qc/0108011
From: SG Ghosh
Date: Fri, 3 Aug 2001 06:45:39 GMT (15kb)
Title: Higher dimensional inhomogeneous dust collapse and cosmic censorship
Authors: S G Ghosh (Science College, Nagpur, India), A Beesham (University of Zululand, RSA)
Comments: 15 pages, LaTeX, 1 figure, 2 tables
Journal-ref: Phys.Rev. D64 (2001) 124005
We investigate the occurrence and nature of a naked singularity in the
gravitational collapse of an inhomogeneous dust cloud described by
higher dimensional Tolman-Bondi space-times. The naked singularities
are found to be gravitationally strong in the sense of Tipler. Higher
dimensions seem to favour black holes rather than naked singularities.
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Paper: gr-qc/0106083
From: abeesham
Date: Tue, 26 Jun 2001 12:58:37 GMT (8kb)
Title: Collapsing shells of radiation in higher dimensional space-time and the cosmic censorship conjecture
Authors: S G Ghosh (Science College, Nagpur, India), R V Saraykar (Nagpur University, India), A
Beesham (Univesity of Zululand, South Africa)
Comments: 9 pages, latex, no figures, accepted in IJMPA
Journal-ref: Int.J.Mod.Phys. A16 (2001) 4481-4488
Gravitational collapse of radiation shells in a non self-similar higher
dimensional spherically symmetric spacetime is studied. Strong
curvature naked singularities form for a highly inhomogeneous
collapse, violating the cosmic censorship conjecture. As a special case,
self similar models can be constructed.
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Paper: gr-qc/0110117
From: Reg Cahill
Date: Mon, 29 Oct 2001 00:41:25 GMT (35kb)
Title: Process Physics: Inertia, Gravity and the Quantum
Authors: Reginald T. Cahill (Flinders University, Australia)
Comments: LaTex, 18 pages 1 eps file. Contribution to the 3rd Australasian Conference on General
Relativity and Gravitation, Perth, Australia, July 2001
Process Physics models reality as self-organising relational or semantic
information using a self-referentially limited neural network model.
This generalises the traditional non-process syntactical modelling of
reality by taking account of the limitations and characteristics of self-
referential syntactical information systems, discovered by Goedel and
Chaitin, and the analogies with the standard quantum formalism and its
limitations. In process physics space and quantum physics are emergent
and unified, and time is a distinct non-geometric process. Quantum
phenomena are caused by fractal topological defects embedded in and
forming a growing three-dimensional fractal process-space. Various
features of the emergent physics are briefly discussed including:
quantum gravity, quantum field theory, 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.
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Paper: gr-qc/0106038
From: uzan
Date: Mon, 11 Jun 2001 14:47:33 GMT (28kb)
Title: Simulated gravity without true gravity in asymmetric brane-world scenarios
Authors: Brandon Carter, Jean-Philippe Uzan, Richard A. Battye, Andrew Mennim
Comments: Latex, 27 pages
Journal-ref: Class.Quant.Grav. 18 (2001) 4871-4896
This article investigates asymmetric brane-world scenarios in the limit
when the bulk gravity is negligible. We show that, even when true self
gravity is negligible, local mass concentrations will be subject to a
mutual attraction force which simulates the effect of Newtonian gravity
in the non-relativistic limit. Cosmological and also post-Newtonian
constraints are examined.
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Paper: hep-th/0105091
From: Andrew Mennim
Date: Thu, 10 May 2001 15:06:23 GMT (20kb)
Title: Einstein equations for an asymmetric brane-world
Authors: Richard A. Battye, Brandon Carter, Andrew Mennim, Jean-Philippe Uzan
Comments: 14 pages, Revtex
Journal-ref: Phys.Rev. D64 (2001) 124007
We consider a brane-world of co-dimension one without the reflection
symmetry that is commonly imposed between the two sides of the
brane. Using the coordinate-free formalism of the Gauss-Codacci
equations, we derive the effective Einstein equations by relating the
local curvature to the matter on the brane in the case when its bare
tension is much larger than the localized matter, and hence show that
Einstein gravity is a natural consequence of such models in the weak
field limit. We find agreement with the recently derived cosmological
case, which can be solved exactly, and point out that such models can
be realized naturally in the case where there is a minimally coupled
form field in the bulk.
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Paper: gr-qc/0106062
From: Neil J. Cornish
Date: Wed, 20 Jun 2001 21:31:52 GMT (7kb)
Title: Chaos and Gravitational Waves
Authors: Neil J. Cornish
Comments: 4 pages, no figures
Journal-ref: Phys.Rev. D64 (2001) 084011
The gravitational waveforms of a chaotic system will exhibit sensitive
dependence on initial conditions. The waveforms of nearby orbits
decohere on a timescale fixed by the largest Lyapunov exponent of the
orbit. The loss of coherence has important observational consequences
for systems where the Lyapunov timescale is short compared to the
chirp timescale. Detectors that rely on matched filtering techniques will
be unable to detect gravitational waves from these systems.
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Paper: gr-qc/0106058
From: Neil J. Cornish
Date (v1): Mon, 18 Jun 2001 23:05:03 GMT (139kb)
Date (revised v2): Mon, 27 Aug 2001 22:23:43 GMT (147kb)
Title: Detecting a stochastic gravitational wave background with the Laser Interferometer Space Antenna
Authors: Neil J. Cornish
Comments: 9 pages, 11 figures. Significant changes to the noise estimates
The random superposition of many weak sources will produce a
stochastic background of gravitational waves that may dominate the
response of the LISA (Laser Interferometer Space Antenna)
gravitational wave observatory. Unless something can be done to
distinguish between a stochastic background and detector noise, the
two will combine to form an effective noise floor for the detector. Two
methods have been proposed to solve this problem. The first is to cross-
correlate the output of two independent interferometers. The second is
an ingenious scheme for monitoring the instrument noise by operating
LISA as a Sagnac interferometer. Here we derive the optimal orbital
alignment for cross-correlating a pair of LISA detectors, and provide
the first analytic derivation of the Sagnac sensitivity curve.
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Paper: astro-ph/0105374
From: Neil J. Cornish
Date: Tue, 22 May 2001 21:19:53 GMT (290kb)
Title: Mapping the gravitational wave background
Authors: Neil J. Cornish
Comments: 16 pages, 6 figures. Submitted to CQG
Journal-ref: Class.Quant.Grav. 18 (2001) 4277-4292
The gravitational wave sky is expected to have isolated bright sources
superimposed on a diffuse gravitational wave background. The
background radiation has two components: a confusion limited
background from unresolved astrophysical sources; and a cosmological
component formed during the birth of the universe. A map of the
gravitational wave background can be made by sweeping a
gravitational wave detector across the sky. The detector output is a
complicated convolution of the sky luminosity distribution, the detector
response function and the scan pattern. Here we study the general de-
convolution problem, and show how LIGO (Laser Interferometric
Gravitational Observatory) and LISA (Laser Interferometer Space
Antenna) can be used to detect anisotropies in the gravitational wave
background.
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Paper: gr-qc/0103075
From: Neil J. Cornish
Date (v1): Wed, 21 Mar 2001 09:06:28 GMT (179kb)
Date (revised v2): Sat, 24 Mar 2001 23:32:51 GMT (180kb)
Title: Space missions to detect the cosmic gravitational-wave background
Authors: Neil J. Cornish, Shane L. Larson
Comments: 22 pages, 7 figures, IOP style, References Added
Journal-ref: Class.Quant.Grav. 18 (2001) 3473-3496
It is thought that a stochastic background of gravitational waves was
produced during the formation of the universe. A great deal could be
learned by measuring this Cosmic Gravitational-wave Background
(CGB), but detecting the CGB presents a significant technological
challenge. The signal strength is expected to be extremely weak, and
there will be competition from unresolved astrophysical foregrounds
such as white dwarf binaries. Our goal is to identify the most promising
approach to detect the CGB. We study the sensitivities that can be
reached using both individual, and cross-correlated pairs of space based
interferometers. Our main result is a general, coordinate free formalism
for calculating the detector response that applies to arbitrary detector
configurations. We use this general formalism to identify some
promising designs for a GrAvitational Background Interferometer
(GABI) mission. Our conclusion is that detecting the CGB is not out of
reach.
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Paper: gr-qc/0111057
From: Antony C Searle
Date: Mon, 19 Nov 2001 00:41:00 GMT (540kb)
Title: GRworkbench: A Computational System Based on Differential Geometry
Authors: Susan M Scott, Benjamin J K Evans, Antony C Searle
Comments: 10 pages, 4 figures, submitted to Proceedings of the Ninth Marcel Grossmann Meeting
We have developed a new tool for numerical work in General
Relativity: GRworkbench. While past tools have been ad hoc,
GRworkbench closely follows the framework of Differential Geometry
to provide a robust and general way of computing on analytically
defined space-times. We discuss the relationship between Differential
Geometry and C++ classes in GRworkbench, and demonstrate their
utility.
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Paper: gr-qc/0110053
From: Antony C Searle
Date: Wed, 10 Oct 2001 00:33:31 GMT (562kb)
Title: Network sensitivity to geographical configuration
Authors: Antony C Searle, Susan M Scott, David E McClelland
Comments: 7 pages, 4 figures, to appear in the proceedings of the 4th Edoardo Amaldi conference
Gravitational wave astronomy will require the coordinated analysis of
data from the global network of gravitational wave observatories.
Questions of how to optimally configure the global network naturally
arise in this context. We propose a formalism to compare different
configurations of the network, using both the coincident network
analysis method and the coherent network analysis method, and
construct a model to compute a figure-of-merit based on the detection
rate for a population of standard-candle binary inspirals. We find that
this measure of network quality is very sensitive to the geographic
location of component detectors under a coincident network analysis,
but comparatively insensitive under a coherent network analysis.
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Paper: gr-qc/0108005
From: Geoffery Ericksson
Date: Thu, 2 Aug 2001 07:53:26 GMT (17kb)
Title: Isotropic singularities in shear-free perfect fluid cosmologies
Authors: Geoffery Ericksson, Susan M. Scott
Comments: 21 pages, 1 figure
Journal-ref: Gen.Rel.Grav. 32 (2000) 425-443
We investigate barotropic perfect fluid cosmologies which admit an
isotropic singularity. From the General Vorticity Result of Scott, it is
known that these cosmologies must be irrotational. In this paper we
prove, using two different methods, that if we make the additional
assumption that the perfect fluid is shear-free, then the fluid flow must
be geodesic. This then implies that the only shear-free, barotropic,
perfect fluid cosmologies which admit an isotropic singularity are the
FRW models.
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Paper: astro-ph/0107321
From: Nelson Nunes
Date: Tue, 17 Jul 2001 20:57:52 GMT (75kb)
Title: Applications of scalar attractor solutions to Cosmology
Authors: S.C.C. Ng (Adelaide), N.J. Nunes (Sussex), F. Rosati (Padova)
Comments: 9 pages, 7 figures. Accepted for publication in PRD
Report-no: SUSX-TH/01-030
Journal-ref: Phys.Rev. D64 (2001) 083510
We develop a framework to study the phase space of a system
consisting of a scalar field rolling down an arbitrary potential with
varying slope and a background fluid, in a cosmological setting. We
give analytical approximate solutions of the field evolution and discuss
applications of its features to the issues of quintessence, moduli
stabilisation and quintessential inflation.
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Paper: astro-ph/0107142
From: David Wiltshire
Date (v1): Sun, 8 Jul 2001 03:30:06 GMT (141kb)
Date (revised v2): Wed, 12 Sep 2001 09:56:45 GMT (193kb)
Title: Future supernova probes of quintessence
Authors: S.C.C. Ng, D.L. Wiltshire
Comments: 13 pages, RevTeX, 7 figures in 9 files, epsf. Revised: statistical tests extended and refined, but
conclusions not significantly changed; references and new figures added
Report-no: ADP-01-21/M97
We investigate the potential of a future supernovae data set, as might be
obtained by the proposed SNAP satellite, to discriminate between two
possible explanations for the observed dimming of the high redshift
type IA supernovae, namely either (i) a cosmological evolution for
which the expansion of the universe has been accelerating for a
substantial range of redshifts $z\goesas1$; or (ii) an unexpected
supernova luminosity evolution over such a redshift range. By
evaluating Bayes factors we show that within the context of spatially
flat model universes with a dark energy the future SNAP data set
should be able to discriminate these two possibilities. Our calculations
assume particular cosmological models with a quintessence field in the
form of a dynamical pseudo Nambu-Goldstone boson (PNGB), and a
simple empirical model of the evolution of peak luminosities of the
supernovae sources which has been recently discussed in the literature.
We also show that the fiducial SNAP data set, simulated with the
assumption of no source evolution, is able to discriminate the PNGB
model from a number of other spatially flat quintessence models which
have been widely studied in the literature, namely those with inverse
power-law, simple exponential and double-exponential potentials.
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Paper: gr-qc/0111059
From: Stefano Liberati
Date: Mon, 19 Nov 2001 18:25:12 GMT (26kb)
Title: Refringence, field theory, and normal modes
Authors: C. Barcelo (Portsmouth U.), S. Liberati (Maryland U.), Matt Visser (Washington U., St. Louis)
Comments: 18 pages, RevTex4
In a previous paper [gr-qc/0104001; Class. Quant. Grav. 18 (2001)
3595-3610] we have shown that the occurrence of curved spacetime
``effective Lorentzian geometries'' is a generic result of linearizing an
arbitrary classical field theory around some non-trivial background
configuration. This observation explains the ubiquitous nature of the
``analog models'' for general relativity that have recently been
developed based on condensed matter physics. In the simple (single
scalar field) situation analyzed in our previous paper, there is a single
unique effective metric; more complicated situations can lead to bi-
metric and multi-metric theories. In the present paper we will
investigate the conditions required to keep the situation under control
and compatible with experiment -- either by enforcing a unique
effective metric (as would be required to be strictly compatible with the
Einstein Equivalence Principle), or at the worst by arranging things so
that there are multiple metrics that are all ``close'' to each other (in
order to be compatible with the {\Eotvos} experiment). The
algebraically most general situation leads to a physical model whose
mathematical description requires an extension of the usual notion of
Finsler geometry to a Lorentzian-signature pseudo-Finsler geometry;
while this is possibly of some interest in its own right, this particular
case does not seem to be immediately relevant for either particle
physics or gravitation. The key result is that wide classes of theories
lend themselves to an effective metric description. This observation
provides further evidence that the notion of ``analog gravity'' is rather
generic.
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Paper: cond-mat/0110211
From: Uwe R. Fischer
Date: Wed, 10 Oct 2001 18:11:14 GMT (15kb)
Title: Riemannian geometry of irrotational vortex acoustics
Authors: Uwe R. Fischer, Matt Visser
Comments: 4 pages, 2 figures, RevTex4
We consider acoustic propagation in an irrotational vortex, using the
technical machinery of differential geometry to investigate the
``acoustic geometry'' that is probed by the sound waves. The acoustic
space-time curvature of a constant circulation hydrodynamical vortex
leads to deflection of phonons at appreciable distances from the vortex
core. The scattering angle for phonon rays is shown to be quadratic in
the small quantity $\Gamma/(2\pi cb)$, where $\Gamma$ is the vortex
circulation, $c$ the speed of sound, and $b$ the impact parameter.
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Paper: gr-qc/0110036
From: visser@tui.wustl.edu (Matt Visser)
Date: Sat, 6 Oct 2001 19:10:22 GMT (19kb)
Title: Towards the observation of Hawking radiation in Bose--Einstein condensates
Authors: Carlos Barcelo (Washington University in Saint Louis) Stefano Liberati (University of Maryland),
Matt Visser (Washington University in Saint Louis)
Comments: revtex4; 5 pages in double-column format
Acoustic analogues of black holes (dumb holes) are generated when a
supersonic fluid flow entrains sound waves and forms a trapped region
from which sound cannot escape. The surface of no return, the acoustic
horizon, is qualitatively very similar to the event horizon of a general
relativity black hole. In particular Hawking radiation (a thermal bath of
phonons with temperature proportional to the ``surface gravity'') is
expected to occur. In this note we consider quasi-one-dimensional
supersonic flow of a Bose--Einstein condensate (BEC) in a Laval
nozzle (converging-diverging nozzle), with a view to finding which
experimental settings could magnify this effect and provide an
observable signal. We identify an experimentally plausible
configuration with a Hawking temperature of order 70 n K; to be
contrasted with a condensation temperature of the order of 90 n K.
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Paper: gr-qc/0109069
From: Sayan Kar
Date: Wed, 19 Sep 2001 17:00:02 GMT (16kb)
Title: R=0 spacetimes and self-dual Lorentzian wormholes
Authors: Naresh Dadhich (IUCAA), Sayan Kar (IITKgp), Sailajananda Mukherji (NBU), Matt Visser
(Washington)
Comments: 8 pages, RevTex two column, one figure
A two-parameter family of spherically symmetric, static Lorentzian
wormholes is obtained as the general solution of the equation
$\rho=\rho_t=0$, where $\rho = T_{ij} u^iu^j$, $\rho_t = (T_{ij} -
{1\over2} T g_{ij}) u^iu^j$, and $u^i u_i =- 1$. This equation
characterizes a class of spacetimes which are ``self dual'' (in the sense
of electrogravity duality). The class includes the Schwarzschild black
hole, a family of naked singularities, and a disjoint family of Lorentzian
wormholes, all of which have vanishing scalar curvature (R=0).
Properties of these spacetimes are discussed. Using isotropic
coordinates we delineate clearly the domains of parameter space for
which wormholes, nakedly singular spacetimes and the Schwarzschild
black hole can be obtained. A model for the required ``exotic'' stress-
energy is discussed, and the notion of traversability for the wormholes
is also examined.
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Paper: hep-th/0109033
From: visser@tui.wustl.edu (Matt Visser)
Date: Wed, 5 Sep 2001 22:27:49 GMT (6kb)
Title: Acoustics in Bose--Einstein condensates as an example of Lorentz symmetry breaking
Authors: Matt Visser (Washington University in Saint Louis), Carlos Barcelo (Washington University in
Saint Louis), Stefano Liberati (U Maryland)
Comments: Presented at CPT01; the Second Meeting on CPT and Lorentz Symmetry; Bloomington,
Indiana; 15--18 Aug 2001. 6 pages. Uses sprocl.sty (World Scientific style file; Latex 209)
To help focus ideas regarding possible routes to the breakdown of
Lorentz invariance, it is extremely useful to explore concrete physical
models that exhibit similar phenomena. In particular, acoustics in Bose-
-Einstein condensates has the interesting property that at low-
momentum the phonon dispersion relation can be written in a
``relativistic'' form exhibiting an approximate ``Lorentz invariance''.
Indeed all of low-momentum phonon physics in this system can be
reformulated in terms of relativistic curved-space quantum field theory.
In contrast, high-momentum phonon physics probes regions where the
dispersion relation departs from the relativistic form and thus violates
Lorentz invariance. This model provides a road-map of at least one
route to broken Lorentz invariance. Since the underlying theory is
manifestly physical this type of breaking automatically avoids
unphysical features such as causality violations. This model hints at the
type of dispersion relation that might be expected at ultra-high energies,
close to the Planck scale, where quantum gravity effects are suspected
to possibly break ordinary Lorentz invariance.
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Paper: gr-qc/0107091
From: visser@tui.wustl.edu (Matt Visser)
Date: Fri, 27 Jul 2001 21:37:42 GMT (31kb)
Title: Faster-than-c signals, special relativity, and causality
Authors: Stefano Liberati (U Maryland), Sebastiano Sonego (U Udine, Italy), Matt Visser (Washington
University in Saint Louis)
Comments: Plain LaTeX2E; 25 pages
Motivated by the recent attention on superluminal phenomena, we
investigate the compatibility between faster-than-c propagation and the
fundamental principles of relativity and causality. We first argue that
special relativity can easily accommodate --- indeed, does not exclude -
-- faster-than-c signalling at the kinematical level. As far as causality is
concerned, it is impossible to make statements of general validity,
without specifying at least some features of the tachyonic propagation.
We thus focus on the Scharnhorst effect (faster-than-c photon
propagation in the Casimir vacuum), which is perhaps the most
plausible candidate for a physically sound realization of these
phenomena. We demonstrate that in this case the faster-than-c aspects
are ``benign'' and constrained in such a manner as to not automatically
lead to causality violations.
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Paper: cond-mat/0106255
From: Michael Stone
Date: Wed, 13 Jun 2001 21:02:14 GMT (18kb)
Title: Wave Equation for Sound in Fluids with Vorticity
Authors: Santiago Esteban Perez Bergliaffa, Katrina Hibberd, Michael Stone, Matt Visser
Comments: RevTeX, 27pages
Subj-class: Condensed Matter; Fluid Dynamics
We use Clebsch potentials and an action principle to derive a closed
system of gauge invariant equations for sound superposed on a general
background flow. Our system reduces to the Unruh (1981) and Pierce
(1990) wave equations when the flow is irrotational, or slowly varying.
We illustrate our formalism by applying it to waves propagating in a
uniformly rotating fluid where the sound modes hybridize with inertial
waves.
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Paper: hep-th/0106111
From: visser@tui.wustl.edu (Matt Visser)
Date: Wed, 13 Jun 2001 22:53:41 GMT (15kb)
Title: Essential and inessential features of Hawking radiation
Authors: Matt Visser (Washington University in Saint Louis)
Comments: JHEP style; 17 pages
There are numerous derivations of the Hawking effect available in the
literature. They emphasise different features of the process, and
sometimes make markedly different physical assumptions. This article
presents a ``minimalist'' argument, and strips the derivation of as much
excess baggage as possible. All that is really necessary is quantum
physics plus a slowly evolving future apparent horizon (*not* an event
horizon). In particular, neither the Einstein equations nor Bekenstein
entropy are necessary (nor even useful) in deriving Hawking radiation.
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Paper: gr-qc/0106002
From: Stefano Liberati
Date: Fri, 1 Jun 2001 20:23:44 GMT (8kb)
Title: Einstein Gravity as an emergent phenomenon?
Authors: Carlos Barcelo, Matt Visser, Stefano Liberati
Comments: 8 pages, Essay awarded an honorable mention in the year 2001 Gravity Research Foundation
essay competition
In this essay we marshal evidence suggesting that Einstein gravity may
be an emergent phenomenon, one that is not ``fundamental'' but rather
is an almost automatic low-energy long-distance consequence of a wide
class of theories. Specifically, the emergence of a curved spacetime
``effective Lorentzian geometry'' is a common generic result of
linearizing a classical scalar field theory around some non-trivial
background. This explains why so many different ``analog models'' of
general relativity have recently been developed based on condensed
matter physics; there is something more fundamental going on. Upon
quantizing the linearized fluctuations around this background
geometry, the one-loop effective action is guaranteed to contain a term
proportional to the Einstein--Hilbert action of general relativity,
suggesting that while classical physics is responsible for generating an
``effective geometry'', quantum physics can be argued to induce an
``effective dynamics''. This physical picture suggests that Einstein
gravity is an emergent low-energy long-distance phenomenon that is
insensitive to the details of the high-energy short-distance physics.
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Paper: gr-qc/0104001
From: visser@tui.wustl.edu (Matt Visser)
Date: Mon, 2 Apr 2001 20:45:27 GMT (20kb)
Title: Analog gravity from field theory normal modes?
Authors: Carlos Barcelo (Washington University in Saint Louis) Stefano Liberati (University of Maryland),
Matt Visser (Washington University in Saint Louis)
Comments: Revtex 4 (beta 5); 12 pages in single-column format
Journal-ref: Class.Quant.Grav. 18 (2001) 3595-3610
We demonstrate that the emergence of a curved spacetime ``effective
Lorentzian geometry'' is a common and generic result of linearizing a
field theory around some non-trivial background. This investigation is
motivated by considering the large number of ``analog models'' of
general relativity that have recently been developed based on
condensed matter physics, and asking whether there is something more
fundamental going on. Indeed, linearization of a classical field theory
(a field theoretic ``normal mode analysis'') results in fluctuations whose
propagation is governed by a Lorentzian-signature curved spacetime
``effective metric''. For a single scalar field, this procedure results in a
unique effective metric, which is quite sufficient for simulating
kinematic aspects of general relativity (up to and including Hawking
radiation). Quantizing the linearized fluctuations, the one-loop effective
action contains a term proportional to the Einstein--Hilbert action,
suggesting that while classical physics is responsible for generating an
``effective geometry'', quantum physics can be argued to induce an
``effective dynamics''. The situation is strongly reminiscent of
Sakharov's ``induced gravity'' scenario, and suggests that Einstein
gravity is an emergent low-energy long-distance phenomenon that is
insensitive to the details of the high-energy short-distance physics. (We
mean this in the same sense that hydrodynamics is a long-distance
emergent phenomenon, many of whose predictions are insensitive to
the short-distance cutoff implicit in molecular dynamics.)
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Paper: gr-qc/0103065
From: visser@tui.wustl.edu (Matt Visser)
Date (v1): Fri, 16 Mar 2001 22:17:43 GMT (12kb)
Date (revised v2): Wed, 22 Aug 2001 20:13:24 GMT (16kb)
Title: Spacetime geometry of static fluid spheres
Authors: Shahinur Rahman, Matt Visser (Washington University in Saint Louis)
Comments: Plain LaTeX 2e --- v2: now 22 pages; minor presentation changes in the first part of the paper -
-- no physics modifications; major additions to the examples section: the Gold-I solution is shown to be
identical to the G-G solution. The interior Schwarzschild, Stewart, Buch5 XIII, de Sitter, anti-de Sitter, and
Einstein solutions are all special cases
We exhibit a simple and explicit formula for the metric of an arbitrary
static spherically symmetric perfect fluid spacetime. This class of
metrics depends on one freely specifiable monotone non-increasing
generating function. We also investigate various regularity conditions,
and the constraints they impose. Because we never make any
assumptions as to the nature (or even the existence) of an equation of
state, this technique is useful in situations where the equation of state is
for whatever reason uncertain or unknown.
To illustrate the power of the method we exhibit a new form of the
``Goldman--I'' exact solution and calculate its total mass. This is a
three-parameter closed-form exact solution given in terms of algebraic
combinations of quadratics. It interpolates between (and thereby
unifies) at least six other reasonably well-known exact solutions.
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Paper: hep-th/0109099
From: David Wiltshire
Date (v1): Wed, 12 Sep 2001 21:32:32 GMT (24kb)
Date (revised v2): Wed, 19 Sep 2001 03:06:09 GMT (24kb)
Title: Brane worlds with bolts
Authors: Jorma Louko, David L. Wiltshire
Comments: 18 pages, 1 eps figure, JHEP3 with epsfig; reference added
Report-no: ADP-00-45/M93
We construct a family of (p+3)-dimensional brane worlds in which the
brane has one compact extra dimension, the bulk has two extra
dimensions, and the bulk closes regularly at codimension two
submanifolds known as bolts. The (p+1)-dimensional low energy
spacetime M_{low} may be any Einstein space with an arbitrary
cosmological constant, the value of the bulk cosmological constant is
arbitrary, and the only fields are the metric and a bulk Maxwell field.
The brane can be chosen to have positive tension, and the closure of the
bulk provides a singularity-free boundary condition for solutions that
contain black holes or gravitational waves in M_{low}. The spacetimes
admit a nonlinear gravitational wave whose properties suggest that the
Newtonian gravitational potential on a flat M_{low} will behave
essentially as the static potential of a massless minimally coupled scalar
field with Neumann boundary conditions. When M_{low} is (p+1)-
dimensional Minkowski with p\ge3 and the bulk cosmological constant
vanishes, this static scalar potential is shown to have the long distance
behaviour characteristic of p spatial dimensions.
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Paper: hep-th/0109093
From: David Wiltshire
Date: Wed, 12 Sep 2001 04:17:34 GMT (62kb)
Title: Spacetime as a membrane in higher dimensions
Authors: G.W. Gibbons, D.L. Wiltshire
Comments: 30 pages, 4 figures in 10 files, epsf. This early brane world paper is being placed on the archive
to make it more easily accessible, as its results are used in a new brane world construction in an
accompanying submission
Journal-ref: Nucl.Phys. B287 (1987) 717
By means of a simple model we investigate the possibility that
spacetime is a membrane embedded in higher dimensions. We present
cosmological solutions of d-dimensional Einstein-Maxwell theory
which compactify to two dimensions. These solutions are analytically
continued to obtain dual solutions in which a (d-2)-dimensional
Einstein spacetime "membrane" is embedded in d-dimensions. The
membrane solutions generalise Melvin's 4-dimensional flux tube
solution. The flat membrane is shown to be classically stable. It is
shown that there are zero mode solutions of the d-dimensional Dirac
equation which are confined to a neighbourhood of the membrane and
move within it like massless chiral (d-2)-dimensional fermions. An
investigation of the spectrum of scalar perturbations shows that a well-
defined mass gap between the zero modes and massive modes can be
obtained if there is a positive cosmological term in (d-2) dimensions or
a negative cosmological term in d dimensions.
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