Subject: ASGRG Newsletter #14
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AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION
Electronic Newsletter -- #14, Spring 2004
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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 30 April, 2005.
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CONTENTS:
* Report on KERR FEST, University of Canterbury, Christchurch,
26-28 August, 2004
* 16th Biennial AIP Congress, ANU, 31 January - 4 February, 2005
* MEMBERSHIP DETAILS ONLINE at
http://www.physics.adelaide.edu.au/ASGRG/members.html
* SUBSCRIPTIONS
* FORTHCOMING MEETINGS
* MEMBERS' ABSTRACTS at gr-qc, June 2004 - November 2004
* ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc,
June 2004 - November 2004
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KERR FEST - BLACK HOLES COME OF AGE
In August around 60 mathematicians, physicists and astronomers from
around the world gathered in Christchurch to celebrate the unique
solution of Einstein's equations given to us by Emeritus Professor
Roy Kerr, this being the year of Roy's 70th birthday. Over the past
7 years the evidence for Kerr black holes has increased dramatically
as many new observations from X-ray satellites have radically changed
our understanding of the role of black holes as central to the life
of the universe, so the Kerr Fest was a timely celebration.
The Kerr solution is by now a "household name" among astrophysicists.
As Andy Fabian, head of the X-ray astronomy group at the University of
Cambridge remarked in his plenary lecture at the meeting: "for the past
ten years I've been living in the Kerr geometry". Fabian, who has
worked on almost every X-ray satellite, including NASA's Chandra mission,
was head of a team that in 1997 produced the first hard evidence that
black holes are indeed rotating.
Since black holes are surfaces in space - so-called event horizons -
from which nothing, not even light, can escape they are naturally very
difficult to observe. However, black holes can be detected by their
influence on nearby luminous stars and gas. A black hole in a binary
system will often suck matter off its partner star, forming a spinning
accretion disk, in which particles accelerated to very high speeds emit
X-rays before finally being swallowed by the black hole. By carefully
examining the redshifts and intensities of these X-ray spectra Fabian's
team has shown that the black holes have to be spinning: the redshifts
are so great that this is the only possibility the equations allow.
The most recent evidence has come from the black hole in the
centre of our own galaxy, which has a mass a few million times that of
the sun. In a paper published in Nature in October 2003, a team of
astronomers led by Reinhard Genzel showed from the 17 minute period of
infrared flares from matter falling into the black hole that it must
be spinning at about half the maximum rate allowed by the Kerr solution.
Fulvio Melia, of the University of Arizona who presented the
Public Lecture, showed a capacity audience in the university's largest
lecture theatre stunning images of our galactic black hole and a movie of
stars orbiting nearby which has been filmed over the past decade.
Yet 41 years ago when Roy first presented his solution, there was a strong
school of thought that black holes could not exist. The word "black hole"
was not even used until the late 1960s, reflecting the paradigm shift
resulting from Kerr's revolution. In 1963 black holes were known
as "frozen stars" or "gravitationally collapsed objects", and were thought
to be of theoretical interest only. The only exact solution known, that
found by Karl Schwarzschild a few weeks after Albert Einstein published
his field equations of general relativity in 1915, described non-rotating
stars and black holes. All compact objects in the universe rotate, and so
until 1963 there were many who believed that the perturbations introduced
by rotation would prevent black hole event horizons ever forming. Roy's
dramatic discovery showed that this was not the case, and since
rotating solutions with event horizons existed, black holes had to be
taken very seriously as actual physical objects of the universe.
As with many major leaps in science, acceptance of the reality of
astrophysical black holes was not immediate. It is ironic that the
first observations of then mysterious quasars were discussed at
the very same Texas symposium in 1963 where Roy first presented his
results to a generally unreceptive audience. As the Kerr solution was
explored further it came to be realised that supermassive Kerr black
holes can explain the engines that power quasars in the centres of
active galaxies.
Without rotation gravity "sucks" leading to rather boring physical
phenomena. With rotation black hole physics becomes very dynamic.
Rotating bodies literally drag space with them. Near the Earth the
effect is tiny, but nonetheless is something we hope to measure soon
with the Gravity Probe B satellite just launched in April. Near a
Kerr black hole frame dragging reaches dramatic proportions. Head on
what you think is a straight line towards a Kerr black hole and the
sky will start spinning even when you are sober! The most energetic
phenomena in the universe - not only quasar jets but also
the huge energies of gamma ray bursts from the most violent supernovae
explosions - are believed to arise from the mining of the spin energy
of rotating black holes. The calculations to understand these
phenomena are only possible with the Kerr solution.
The Kerr solution will become ever more important in the next two
decades when we start to detect the gravitational waves - ripples in
the fabric of space - that arise when two massive objects such as black
holes collide. Maurice van Putten of MIT gave us a glimpse of some of
these prospects in his lecture.
Of special note were the lectures from some of the legendary characters in
the history of black holes, such as Brandon Carter, who perhaps did
more than anyone to explore the properties of the Kerr geometry, and
David Robinson who completed the theorems that showed the Kerr solution
is the unique rotating black hole solution of Einstein's equations.
(Brandon hails from Sydney originally, and David from Auckland meaning
that the antipodean connection with black holes extends well beyond Roy's
own contribution.)
Other plenary lectures at the meeting ranged over mathematical studies of
the Kerr geometry (Zoltan Perjes, Susan Scott), astrophysical topics
(Josh Goldberg, Remo Ruffini), and quantum gravity (Steven Carlip, Gary
Horowitz, Matt Visser). There was an interesting set of contributed talks,
and Roy entertained everyone with a historical talk in his laconic style.
The banquet at the Ilam Homestead was a singular occasion, where a number
of anecdotes about Roy were recounted. The party lasted until they threw
us out at 11pm. After the Saturday lectures there was an excursion to the
Canterbury ring laser (world's largest Sagnac interferometer) in the
Cashmere cavern, and as it was a rain-drenched afternoon Anneke Wiltshire
served mulled wine to those waiting their turn for the cavern tour at
her home, conveniently a stone's throw away.
All in all the conference was a splendid success. The financial support
of the NZIMA, the MacDiarmid Institute, the Marsden Fund and the UC
Department of Mathematics and Statistics is gratefully acknowledged.
A special commemorative volume based on the plenary lectures is due to
be published in 2005 by Cambridge University Press. The volume will
be dedicated to the memory of Zoltan Perjes, who tragically passed away
two months after the meeting, after a long illness.
The conference has also rekindled Roy's own interest in the gravitational
two-body problem, something which he looked at in his PhD thesis in
Cambridge before he found his solution, and which is at present of immense
topical interest for understanding the signals to be seen by gravitational
wave detectors. Roy is now an active member of the relativity and
gravitation group at Canterbury, coming in daily to an office a few
doors from mine, and next year he will be taking up a position at the
University of Arizona.
The crowning highlight at the Kerr Fest was the announcement by
Remo Ruffini that Roy will receive the Grossmann Award at the
next Marcel Grossmann Meeting in St Petersburg in 2006. In place of a
medal recipients (in the past including Stephen Hawking and Roger
Penrose) receive the TEST sculpture, which fittingly enough is a
representation, cast in silver, of particle motion in the vicinity of
a Kerr black hole. ("Ah but it's coordinate dependent" whispered Roy;
too bad: it certainly is equal to Remo's proclamation: "e bella!")
- David Wiltshire
(Dept of Physics and Astronomy, University of Canterbury)
A number of presentations and photos from the Kerr Fest are
available online at http://www2.phys.canterbury.ac.nz/kerrfest/
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16TH BIENNIAL AIP CONGRESS, ANU, 31 JANUARY - 4 FEBRUARY, 2005
The 16th Biennial Congress of the Australian Institute of Physics, entitled
"Physics for the Nation", will be held at the Manning Clark Centre and
Melville Hall on the Australian National University Campus, Canberra, from
Monday 31 January to Friday 4 February 2005. The ANU is located on the north
side of Lake Burley Griffin - the centrepiece of Canberra - on a 150-hectare
site between native bushland and the city centre.
The Congress will mark the UN International Year of Physics 2005 - celebrating
100 years since Einstein's discoveries in relativity, quantum theory and
Brownian motion - and will highlight the contribution of physics to Australia.
The occasion will bring together an unusually large and diverse group of
scientists from different disciplines who share a common interest in physics.
To celebrate the 2005 International Year of Physics, the Congress aims to be
the largest-ever gathering of Australian physicists. For the first time it will
encompass a broad range of disciplines in which Physics plays an important
role including for example astronomy, bio/medical physics, education,
environmental physics, geophysics, meteorology/climate change, and renewable
energy systems.
There will be nine plenary talks which will be presented by outstanding,
internationally renowned physicists who have a track record of delivering
high quality talks to a broad physics audience. They will include two Nobel
Prize Winners in Physics Professor Steven Chu (1997) and Professor Tony
Leggett (2003).
Two plenary speakers of particular interest to ASGRG members are Professor
Karsten Danzmann of the Max Planck Institute for Gravitational Physics,
Hannover, Germany, who will speak on "Gravitational Wave Detectors on the
Earth and in Deep Space" on Tuesday 1 February, 0830-0915, and Dr Catherine
Cesarsky of the European Southern Observatory, Garching, Germany, whose talk
called "A Golden Age for Astronomy" will be delivered on Thursday 3 February,
0915-1000.
The remainder of the oral presentations in the Congress will comprise six
parallel sessions, each representing a particular discipline group. In these
sessions, keynote speakers will present leading developments (duration 35
minutes + 5 minutes question time). The remainder of the sessions will
comprise shorter contributed talks (15 + 5 minutes), and there will be four
common poster sessions for all the discipline groups.
The two ASGRG parallel sessions are scheduled for:
1. Tuesday 1 February, 1040-1220
Chair: Peter Veitch
Speakers: Blair, Brooks, Gray, Ashley, Ware
2. Tuesday 1 February, 1400-1540
Chair: David McClelland
Speakers: Hartnett, Scott, Davies, Whale, Van Putten
The ASGRG poster session will be held on Tuesday 1 February, 1930-2130.
For more information, visit the Congress website at:
http://aipcongress2005.anu.edu.au/
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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 2005 - June 2006 subscriptions are requested, if you wish to
pay for July 2006 - June 2007 at the same time, it may simplify matters.
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FORTHCOMING MEETINGS
December 13-17, 2004: 22nd Texas Symposium on Relativistic Astrophysics
Stanford University, California
http://texasatstanford.slac.stanford.edu/
December 15-18, 2004: 9th Annual Gravitational Wave Data Analysis Workshop
Annecy-le-Vieux Particle Physics Laboratory, Annecy, France
http://lappweb.in2p3.fr/GWDAW9/
December 25-27, 2004: Rironkon Symposium: "Astronomy Next Generation"
Niigata University, Tokyo, Japan
http://astro1.sc.niigata-u.ac.jp/sympo04/
January 11-14, 2005: International Conference on Relativity (ICR-2005)
Amravati, India
January 16-22, 2005: 2005 Aspen Winter Conference on Gravitational Waves
Aspen, Colorado
January 21-25, 2005: "Relativistic Coordinates, Reference and Positioning
Systems"
University of Salamanca, Spain
http://www3.usal.es/~ft/rc2005/index_english.html
January 20-26, 2005: GR-12-RUS 12 Russian Gravitational Conference:
International Conference on Gravitation, Cosmology and
Astrophysics
Kazan, Russia
http://www.rgs.da.ru/
February 16-19, 2005: 4th TAMA Symposium
Osaka, Japan
http://www.gw.hep.osaka-cu.ac.jp/TAMAsympo4/
March 9-15, 2005: HGR7: Seventh International Conference on the History of
General Relativity
La Orotava, Tenerife, Spain
http://nti.educa.rcanaria.es/fundoro/einstein_2nd/einstein_web_a.htm
March 14-28, 2005: "Apples with Apples 3": Numerical Relativity Comparisons
and Tests
Cordoba, Argentina
http://www.appleswithapples.org/index.html
March 18-19, 2005: 8th Eastern Gravity Meeting
Wake Forest University, Winston-Salem, North Carolina
http://www.wfu.edu/%7Ecookgb/EGM8/
March 29 - April 2, 2005: "Spacetime in Action: 100 Years of Relativity"
Pavia, Italy
http://www.pv.infn.it/%7Espacetimeinaction/
April 5-8, 2005: "Geometry and Physics After 100 Years of Einstein's Relativity:
10 Years of the Albert Einstein Institute"
Albert Einstein Institute, Potsdam, Germany
http://www.aei.mpg.de/
May 29 - June 18, 2005: "LISA: Data Analysis, Sources, and Science"
Aspen Center for Physics 2005 Summer Workshop
Aspen, Colorado
http://www.astro.northwestern.edu/AspenS05/index.html
June 7-11, 2005: "Physics in the 21st Century: 100 Years after Einstein's
'Annus Mirabilis'"
University of Zurich, Switzerland
http://www.itp.phys.ethz.ch/einstein/
June 13-24, 2005: Summer School in Gravitational Wave Astronomy
University of Texas at Brownsville
http://cgwa.phys.utb.edu/Events/SummerSchool.php
June 19-25, 2005: Fourth International Symposium on Experimental Gravitation
Kazan, Tatarstan, Russia
http://www.dulkyn.org.ru/conference.html
June 27 - July 1, 2005: Yukawa Kyoto International Seminar 2005 (YKIS2005):
"The Next Chapter in Einstein's Legacy"
Kyoto University, Japan
http://www2.yukawa.kyoto-u.ac.jp/%7Eykis2005/
July 11-15, 2005: 13th General Conference of the European Physical Society
"Beyond Einstein: Physics for the 21st Century"
University of Bern, Switzerland
http://www.eps13.org/
July 11-22, 2005: "Einstein's Century" International Conference
Paris, France
http://einstein2005.obspm.fr/indexr.html
September 12-16, 2005: Fourth Meeting on Constrained Dynamics and Quantum Gravity
Cala Gonone, Sardinia, Italy
http://www.phy.olemiss.edu/GR/qg05/
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MEMBERS' ABSTRACTS at gr-qc, June 2004 - November 2004
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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gr-qc/0406022
From: Hossein Farajollahi
Date: Mon, 7 Jun 2004 12:51:31 GMT (13kb)
Stochastic quantisation of locally supersymmetric models
Authors: Hossein Farajollahi, Hugh Luckock
Comments: 19 pages. To be published in "International Journal of Theoretical
Physics, Group Theory and Nonlinear Optics"
Stochastic quantisation normally involves the introduction of a fictitious
extra time parameter, which is taken to infinity so that the system evolves
to an equilibrium state.In the case of a locally supersymmetric theory, an
interesting new possibility arises due to the existence of a Nicolai map. In
this case it turns out that no additional time parameter is required, as the
existence of the Nicolai map ensures that the same job can be done by the
existing time parameter after Euclideanisation. This provides the quantum
theory with a natural probabilistic interpretation, without any reference to
the concept of an inner product or a Hilbert space structure.
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gr-qc/0406024
From: Hossein Farajollahi
Date: Mon, 7 Jun 2004 12:33:58 GMT (251kb)
World-line observables and clocks in General Relativity
Authors: Hossein Farajollahi
Comments: 16 pages. To be published in "International Journal of Theoretical
Physics, Group Theory and Nonlinear Optics"
A proposal for the issue of time and observables in any parameterized theory
such as general relativity is addressed. Introduction of a gauge potential
3-form A in the theory of relativity enables us to define a gauge-invariant
quantity which can be used by observers as a clock to measure the passage of
time. This dynamical variable increases monotonically and continuously along
a world line. Then we define world line observables to be any covariantly
defined quantity obtained from the field configurations on any such causal
past with dynamical time T.
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gr-qc/0408006
From: Adrian P. Gentle
Date: Mon, 2 Aug 2004 16:59:41 GMT (109kb)
Regge calculus: a unique tool for numerical relativity
Authors: Adrian P. Gentle
Comments: 7 pages; brief review not previously available on arXiv.org
Journal-ref: Gen.Rel.Grav. 34 (2002) 1701-1718
The application of Regge calculus, a lattice formulation of general
relativity, is reviewed in the context of numerical relativity. Particular
emphasis is placed on problems of current computational interest, and the
strengths and weaknesses of the lattice approach are highlighted. Several
new and illustrative applications are presented, including initial data for
the head on collision of two black holes, and the time evolution of vacuum
axisymmetric Brill waves.
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gr-qc/0406106
From: Daniel A. Shaddock
Date: Fri, 25 Jun 2004 23:50:57 GMT (122kb)
Post-processed time-delay interferometry for LISA
Authors: D. A. Shaddock, B. Ware, R. E. Spero, M. Vallisneri
Comments: 14 pages, 6 figures
High-precision interpolation of LISA phase measurements allows signal
reconstruction and formulation of Time-Delay Interferometry (TDI)
combinations to be conducted in post-processing. The reconstruction is based
on phase measurements made at approximately 10 Hz, at regular intervals
independent of the TDI delay times. Interpolation introduces an error less
than 1e-8 with continuous data segments as short as two seconds in duration.
Potential simplifications in the design and operation of LISA are presented.
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gr-qc/0406083
From: Francisco Lobo
Date (v1): Mon, 21 Jun 2004 11:07:42 GMT (22kb)
Date (revised v2): Sun, 31 Oct 2004 13:32:19 GMT (23kb)
Fundamental limitations on "warp drive" spacetimes
Authors: Francisco S. N. Lobo, Matt Visser
Comments: 18 pages, Revtex4. V2: one reference added, some clarifying
comments and discussion, no physics changes, accepted for publication in
Classical and Quantum Gravity
Journal-ref: Class.Quant.Grav. 21 (2004) 5871-5892
"Warp drive" spacetimes are useful as "gedanken-experiments" that force us
to confront the foundations of general relativity, and among other things,
to precisely formulate the notion of "superluminal" communication. We verify
the non-perturbative violation of the classical energy conditions of the
Alcubierre and Natario warp drive spacetimes and apply linearized gravity to
the weak-field warp drive, testing the energy conditions to first and second
order of the non-relativistic warp-bubble velocity. We are primarily
interested in a secondary feature of the warp drive that has not previously
been remarked upon, if it could be built, the warp drive would be an example
of a "reaction-less drive". For both the Alcubierre and Natario warp drives
we find that the occurrence of significant energy condition violations is not
just a high-speed effect, but that the violations persist even at arbitrarily
low speeds.
An interesting feature of this construction is that it is now meaningful to
place a finite mass spaceship at the center of the warp bubble, and compare
the warp field energy with the mass-energy of the spaceship. There is no hope
of doing this in Alcubierre's original version of the warp-field, since by
definition the point in the center of the warp bubble moves on a geodesic and
is "massless". That is, in Alcubierre's original formalism and in the Natario
formalism the spaceship is always treated as a test particle, while in the
linearized theory we can treat the spaceship as a finite mass object. For
both the Alcubierre and Natario warp drives we find that even at low speeds
the net (negative) energy stored in the warp fields must be a significant
fraction of the mass of the spaceship.
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gr-qc/0408022
From: Matt Visser
Date (v1): Mon, 9 Aug 2004 13:46:46 GMT (805kb)
Date (revised v2): Wed, 1 Sep 2004 12:38:33 GMT (794kb)
Causal structure of acoustic spacetimes
Authors: Carlos Barcelo, Stefano Liberati, Sebastiano Sonego, Matt Visser
Comments: 51 pages, 39 figures (23 colour figures, colour used to convey
physics information.) V2: Two references added, some additional discussion
of maximal analytic extension, plus minor cosmetic changes
The so-called ``analogue models of general relativity'' provide a number of
specific physical systems, well outside the traditional realm of general
relativity, that nevertheless are well-described by the differential
geometry of curved spacetime. Specifically, the propagation of acoustic
disturbances in moving fluids are described by ''effective metrics'' that
carry with them notions of ''causal structure'' as determined by an exchange
of sound signals. These acoustic causal structures serve as specific examples
of what can be done in the presence of a Lorentzian metric without having
recourse to the Einstein equations of general relativity. (After all, the
underlying fluid mechanics is governed by the equations of traditional
hydrodynamics, not by the Einstein equations.) In this article we take a
careful look at what can be said about the causal structure of acoustic
spacetimes, focusing on those containing sonic points or horizons, both with
a view to seeing what is different from standard general relativity, and to
seeing what the similarities might be.
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gr-qc/0409014
From: Matt Visser
Date: Fri, 3 Sep 2004 06:18:12 GMT (35kb)
Vortex geometry for the equatorial slice of the Kerr black hole
Authors: Matt Visser, S. E. Ch. Weinfurtner
Comments: 24 pages, 5 figures (some use of colour)
The spacetime geometry on the equatorial slice through a Kerr black hole is
formally equivalent to the geometry felt by phonons entrained in a rotating
fluid vortex. We analyse this situation in some detail: First, we find the
most general ''acoustic geometry'' compatible with the fluid dynamic
equations in a collapsing/expanding perfect-fluid line vortex. Second, we
demonstrate that there is a suitable choice of coordinates on the equatorial
slice through a Kerr black hole that puts it into this vortex form; though
it is not possible to put the entire Kerr spacetime into perfect-fluid
''acoustic'' form. Finally, we briefly discuss the implications of this
formal equivalence; both with respect to gaining insight into the Kerr
spacetime and with respect to possible vortex-inspired experiments.
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cond-mat/0409639
From: Matt Visser
Date (v1): Fri, 24 Sep 2004 07:36:50 GMT (9kb)
Date (revised v2): Sat, 25 Sep 2004 02:34:28 GMT (9kb)
Massive phonon modes from a BEC-based analog model
Authors: Matt Visser, Silke Weinfurtner
Comments: 4 pages; uses revtex4
Subj-class: Statistical Mechanics
Two-component BECs subject to laser-induced coupling exhibit a complicated
spectrum of excitations, which can be viewed as two interacting phonon modes.
We study the conditions required to make these two phonon modes decouple.
Once decoupled, the phonons not only can be arranged travel at different
speeds, but one of the modes can be given a mass -- it exhibits the
dispersion relation of a massive relativistic particle: omega =
sqrt{omega_0^2 + c^2 k^2}. This is a new and unexpected excitation mode for
the coupled BEC system. Apart from its intrinsic interest to the BEC
community, this observation is also of interest for the ''analogue gravity''
programme, as it opens the possibility for using BECs to simulate massive
relativistic particles in an effective ''acoustic geometry''.
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gr-qc/0410113
From: Matt Visser
Date: Thu, 21 Oct 2004 22:58:55 GMT (19kb)
Interpreting doubly special relativity as a modified theory of measurement
Authors: Stefano Liberati (SISSA, Trieste, Italy), Sebastiano Sonego (Udine,
Italy), Matt Visser (Victoria, New Zealand)
Comments: 18 pages, plain LaTeX2E
In this article we develop a physical interpretation for the deformed (doubly)
special relativity theories (DSRs), based on a modification of the theory of
measurement in special relativity. We suggest that it is useful to regard the
DSRs as reflecting the manner in which quantum gravity effects induce Planck-
suppressed distortions in the measurement of the "true" energy and momentum.
This interpretation provides a framework for the DSRs that is manifestly
consistent, non-trivial, and in principle falsifiable. However, it does so at
the cost of demoting such theories from the level of "fundamental" physics to
the level of phenomenological models -- models that should in principle be
derivable from whatever theory of quantum gravity one ultimately chooses to
adopt.
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gr-qc/0411034
From: Matt Visser
Date: Mon, 8 Nov 2004 19:46:20 GMT (9kb)
Effective refractive index tensor for weak field gravity
Authors: Petarpa Boonserm, Celine Cattoen, Tristan Faber, Matt Visser, Silke
Weinfurtner (Victoria University, New Zealand)
Comments: 8 pages, no figures, uses iopart.cls
Gravitational lensing in a weak but otherwise arbitrary gravitational field
can to linearized order be described in terms of an analogy that uses a 3x3
tensor to characterize an "effective refractive index". If the sources
generating the gravitational field all have small internal fluxes, stresses,
and pressures, then the tensor is automatically isotropic and the "effective
refractive index" is simply a scalar that can be determined in terms of a
classic result involving the Newtonian gravitational potential. In contrast
if anisotropic stresses are ever important then the gravitational field acts
similarly to an anisotropic crystal. We derive simple formulae for the
refractive index tensor, and indicate some situations in which this will be
important.
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gr-qc/0411131
From: Matt Visser
Date: Sat, 27 Nov 2004 19:10:06 GMT (8kb)
Cosmography: Cosmology without the Einstein equations
Authors: Matt Visser
Comments: 7 pages; uses iopart.cls setstack.sty. Based on a talk presented at
ACRGR4, the 4th Australasian Conference on General Relativity and Gravitation,
Monash University, Melbourne, January 2004. To appear in the proceedings, in
General Relativity and Gravitation
How much of modern cosmology is really cosmography? How much of modern
cosmology is independent of the Einstein equations? (Independent of the
Friedmann equations?) These questions are becoming increasingly germane -- as
the models cosmologists use for the stress-energy content of the universe
become increasingly baroque, it behoves us to step back a little and carefully
disentangle cosmological kinematics from cosmological dynamics. The use of
basic symmetry principles (such as the cosmological principle) permits us to
do a considerable amount, without ever having to address the vexatious issues
of just how much "dark energy", "dark matter", "quintessence", and/or "phantom
matter" is needed in order to satisfy the Einstein equations. This is the sub-
sector of cosmology that Weinberg refers to as "cosmography", and in this
article I will explore the extent to which cosmography is sufficient for
analyzing the Hubble law and so describing many of the features of the
universe around us.
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gr-qc/0410011
From: Steven Detweiler
Date: Mon, 4 Oct 2004 16:20:41 GMT (39kb)
Scalar field self-force effects on orbits about a Schwarzschild black hole
Authors: Luz Maria Diaz-Rivera, Eirini Messaritaki, Bernard F. Whiting,
Steven Detweiler
Comments: 15 pages, 8 figures
For a particle of mass mu and scalar charge q, we compute the effects of the
scalar field self-force upon circular orbits, upon slightly eccentric orbits
and upon the innermost stable circular orbit of a Schwarzschild black hole of
mass M. For circular orbits the self force is outward and causes the angular
frequency at a given radius to decrease. For slightly eccentric orbits the
self force decreases the rate of the precession of the orbit. The effect of
the self force moves the radius of the innermost stable circular orbit inward
by 0.122701 q^2/mu, and it increases the angular frequency of the ISCO by the
fraction 0.0291657 q^2/mu M.
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physics/0406156
From: David Wiltshire
Date: Wed, 30 Jun 2004 10:19:46 GMT (150kb)
Direct measurement of diurnal polar motion by ring laser gyroscopes
Authors: K.U. Schreiber, A. Velikoseltsev, M. Rothacher, T. Klugel,
G.E. Stedman, D.L. Wiltshire
Comments: 5 pages, 4 figures, agu2001.cls
Subj-class: Geophysics; Space Physics
Journal-ref: J.Geophys.Res. 109 (2004) B06405
DOI: 10.1029/2003JB002803
We report the first direct measurements of the very small effect of forced
diurnal polar motion, successfully observed on three of our large ring
lasers, which now measure the instantaneous direction of Earth's rotation
axis to a precision of 1 part in 10^8 when averaged over a time interval of
several hours. Ring laser gyroscopes provide a new viable technique for
directly and continuously measuring the position of the instantaneous
rotation axis of the Earth and the amplitudes of the Oppolzer modes. In
contrast, the space geodetic techniques (VLBI, SLR, GPS, etc.) contain no
information about the position of the instantaneous axis of rotation of the
Earth, but are sensitive to the complete transformation matrix between the
Earth-fixed and inertial reference frame. Further improvements of gyroscopes
will provide a powerful new tool for studying the Earth's interior.
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hep-th/0408215
From: S. Mignemi
Date (v1): Fri, 27 Aug 2004 16:33:06 GMT (14kb)
Date (revised v2): Wed, 8 Sep 2004 16:11:05 GMT (24kb)
Date (revised v3): Wed, 15 Sep 2004 16:14:52 GMT (24kb)
Date (revised v4): Mon, 15 Nov 2004 16:50:12 GMT (32kb)
Multi-scalar black holes with contingent primary hair: Mechanics and
stability
Authors: S. Mignemi, D.L. Wiltshire
Comments: 10 pages, RevTeX4, 6 figures, graphicx. v2: Substantial new
sections and results added from authors' joint unpublished manuscript dated
2000, doubling the length of the paper. v3: references added.
v4: Small additions (extra figures etc) to agree with published version
Report-no: ADP-00-46/M94
We generalize a class of magnetically charged black holes holes non-minimally
coupled to two scalar fields previously found by one of us [gr-qc/9910041] to
the case of multiple scalar fields. The black holes possess a novel type of
primary scalar hair, which we call a contingent primary hair: although the
solutions possess degrees of freedom which are not completely determined by
the other charges of the theory, the charges necessarily vanish in the
absence of the magnetic monopole. Only one constraint relates the black hole
mass to the magnetic charge and scalar charges of the theory. We obtain a
Smarr-type thermodynamic relation, and the first law of black hole
thermodynamics for the system. We further explicitly show in the two-scalar-
field case that, contrary to the case of many other hairy black holes, the
black hole solutions are stable to radial perturbations.
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gr-qc/0411037
From: Robin W. Tucker
Date: Mon, 8 Nov 2004 16:55:25 GMT (54kb)
Twisted Electromagnetic Modes and Sagnac Ring-Lasers
Authors: David A. Burton, Adam Noble, Robin W. Tucker, David L. Wiltshire
Comments: LaTeX 31 pages, 3 Figures
Report-no: Lancaster 8-11-2004
A new approximation scheme, designed to solve the covariant Maxwell equations
inside a rotating hollow slender conducting cavity (modelling a ring-laser),
is constructed. It is shown that for well-defined conditions there exist TE
and TM modes with respect to the longitudinal axis of the cavity. A twisted
mode spectrum is found to depend on the integrated Frenet torsion of the
cavity and this in turn may affect the Sagnac beat frequency induced by a
non-zero rotation of the cavity. The analysis is motivated by attempts to use
ring-lasers to measure terrestrial gravito-magnetism or the Lense-Thirring
effect produced by the rotation of the Earth.
******************************************************************************
ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc,
June 2004 - November 2004
The LIGO Scientific Collaboration is a consortium of scientific institutions
doing work on the Laser Interferometer Gravitational-Wave Observatory
(LIGO), which consists of two laser interferometers 3030 km apart, one at
Hanford, Washington State and the other at Livingston, Louisiana. The LIGO
Scientific Collaboration includes ASGRG members David McClelland, Susan Scott
and Antony Searle, who are all at the Australian National University.
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gr-qc/0410007
From: Graham Woan
Date: Fri, 1 Oct 2004 20:01:22 GMT (100kb)
Limits on gravitational wave emission from selected pulsars using LIGO data
Authors: The LIGO Scientific Collaboration: B. Abbott, et al, M. Kramer,
A.G. Lyne
Comments: 6 pages, 2 figures
Report-no: LIGO-P040008-A-Z
We place direct upper limits on the strain of the gravitational waves from 28
isolated radio pulsars by a coherent multi-detector analysis of the data
collected during the second science run of the LIGO interferometric detectors.
These are the first direct upper limits for 26 of the 28 pulsars. We use
coordinated radio observations for the first time to build radio-guided phase
templates for the expected gravitational wave signals. The unprecedented
sensitivity of the detectors allow us to set strain upper limits as low as a
few times $10^{-24}$. These strain limits translate into limits on the
equatorial ellipticities of the pulsars, which are smaller than $10^{-5}$ for
the four closest pulsars.
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