Subject: ASGRG Newsletter #15
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AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION
Electronic Newsletter -- #15, 2005
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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, 2006.
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CONTENTS:
* POSTPONEMENT OF 5TH AUSTRALASIAN CONFERENCE ON GENERAL RELATIVITY
AND GRAVITATION (ACGRG5)
* REPLACEMENT OF ASGRG TREASURER
* MEMBERSHIP DETAILS ONLINE at
http://www.physics.adelaide.edu.au/ASGRG/members.html
* SUBSCRIPTIONS
* FORTHCOMING MEETINGS
* MEMBERS' ABSTRACTS at gr-qc, December 2004 - November 2005
* ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc,
December 2004 - November 2005
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Fifth Australasian Conference
on General Relativity & Gravitation
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ACGRG5 POSTPONED
The Fifth Australasian Conference was originally to have been held
in Christchurch in 2006. However, we are unfortunately unable to find
a mutually convenient date in which to run the meeting, the suggestion
of January being impossible for the local organiser because of other
commitments on one hand, and clashes between New Zealand and
Australian semester breaks at other times in the year on the other.
Since there are two major international conferences in our region soon-
the Texas meeting in Melbourne in December 2006 and GR18 in Sydney
2007 - it does not seem practical to be running another meeting in
2006 and so the ASGRG committee propose that we postpone the 2006 BGM
until the time of GR18 in Sydney when a majority of members will be
present. The venue for the next ACGRG will be decided then.
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REPLACEMENT OF ASGRG TREASURER
Antony Searle resigned from his position as ASGRG Treasurer on 22 November
2005. We would like to thank Antony for all his efforts on behalf of the
Society over the years.
The Executive Committee decided unanimously to elect John Steele as the
new ASGRG Treasurer to fill the casual vacancy caused by Antony's departure.
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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 2006 - June 2007 subscriptions are requested, if you wish to
pay for July 2007 - June 2008 at the same time, it may simplify matters.
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FORTHCOMING MEETINGS
March 2-6, 2006: International Conference on Gravitation, Cosmology and Astrophysics
Moscow, Russia
http://www.rgs.da.ru/
July 23-29, 2006: 11th Marcel Grossman Meeting on General Relativity (MG11)
Freie Univesitaet, Berlin
http://www.icra.it/MG/mg11/
December 11-15, 2006: Texas in Australia: 23rd Texas Symposium on Relativistic Astrophysics
University of Melbourne, Melbourne, Australia
July 8-13, 2007: 18th International Conference on General Relativity and Gravitation (GR18)
Darling Harbour, Sydney, Australia
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MEMBERS' ABSTRACTS at gr-qc, December 2004 - November 2005
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/0505160
From: Malcolm Anderson
Date: Tue, 31 May 2005 15:04:17 GMT (231kb)
Self-Similar Evaporation of a Rigidly-Rotating Cosmic String Loop
Authors: Malcolm Anderson
Comments: 41 pages, 5 figures. Accepted for publication in Classical and
Quantum Gravity
Journal-ref: Class.Quant.Grav. 22 (2005) 2539-2568
The gravitational back-reaction on a certain type of rigidly-rotating
cosmic string loop, first discovered by Allen, Casper and Ottewill, is
studied at the level of the weak-field approximation. The near-field
metric perturbations are calculated and used to construct the self-
acceleration vector of the loop. Although the acceleration vector is
divergent at the two kink points on the loop, its net effect on the
trajectory over a single oscillation period turns out to be finite. The
net back-reaction on the loop over a single period is calculated using a
method due to Quashnock and Spergel, and is shown to induce a uniform
shrinkage of the loop while preserving its original shape. The loop
therefore evolves by self-similar evaporation.
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gr-qc/0505103
From: Dr. Bikash Chandra Paul
Date: Fri, 20 May 2005 07:40:14 GMT (16kb)
Emergent Universe in Starobinsky Model
Authors: S. Mukherjee, B. C. Paul, S. D. Maharaj, A. Beesham
Comments: 12 pages, 3 figures
We present an emergent universe scenario making use of a new solution of
the Starobinsky model. The solution belongs to a one parameter family of
solutions, where the parameter is determined by the number and the species
(spin-values) of primordial fields. The general features of the model have
also been studied.
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gr-qc/0502079
From: Chunnong Zhao
Date: Fri, 18 Feb 2005 02:46:01 GMT (209kb)
Parametric instabilities and their control in advanced interferometer GW
detectors
Authors: C. Zhao, L. Ju, J. Degallaix, S. Gras, D. G. Blair
Comments: 5 pages, 4 figures
Journal-ref: Phys.Rev.Lett. 94 (2005) 121102
A detailed simulation of Advanced LIGO test mass optical cavities shows
that parametric instabilities will excite acoustic modes in the test masses
in the frequency range 28-35 kHz and 64-72 kHz. Using nominal Advanced LIGO
optical cavity parameters with fused silica test masses, parametric
instability excites 7 acoustic modes in each test mass, with parametric
gain R up to 7. For the alternative sapphire test masses only 1 acoustic
mode is excited in each test mass with R ~ 2. Fine tuning of the test mass
radii of curvature cause the instabilities to sweep through various modes
with R as high as ~2000. Sapphire test mass cavities can be tuned to
completely eliminate instabilities using thermal g-factor tuning with
negligible degradation of the noise performance. In the case of fused silica
test mass, instabilities can be minimized but not eliminated.
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gr-qc/0507006
From: Brandon Carter
Date: Sun, 3 Jul 2005 13:50:51 GMT (35kb)
Covariant Newtonian and Relativistic dynamics of (magneto)-elastic solid
model for neutron star crust
Authors: Brandon Carter, Elie Chachoua, Nicolas Chamel
Comments: 39 pages Latex
This work develops the dynamics of perfectly elastic solid model for
application to the outer crust of a magnetised neutron star. Particular
attention is given to the Noether identities responsible for energy-momentum
conservation, using a formulation that is fully covariant, not only (as is
usual) in a fully relativistic treatment but also (sacrificing accuracy and
elegance for economy of degrees of gravitational freedom) in the technically
more complicated case of the Newtonian limit. The results are used to obtain
explicit (relativistic and Newtonian) formulae for the propagation speeds of
generalised (Alfven type) magneto-elastic perturbation modes.
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gr-qc/0504012
From: Edward Porter
Date: Mon, 4 Apr 2005 18:41:16 GMT (24kb)
Detecting Galactic Binaries with LISA
Authors: Neil J. Cornish, Edward K. Porter
Comments: 6 pages-1 figure, Proceedings of GWDAW 9, Submitted to Classical
and Quantum Gravity
One of the main sources of gravitational waves for the LISA space-borne
interferometer are galactic binary systems. The waveforms for these sources
are represented by eight parameters, of which four are extrinsic, and four
are intrinsic to the system. Geometrically, these signals exist in an 8-d
parameter space. By calculating the metric tensor on this space, we
calculate the number of templates needed to search for such sources. We show
in this study that below a particular monochromatic frequency, we can ignore
one of the intrinsic parameters and search over a 7-d space. Beyond this
frequency, we have a sudden change in dimensionality of the parameter space
from 7 to 8 dimensions, which results in a change in the scaling of the
growth of template number as a function of monochromatic frequency.
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gr-qc/0504071
From: Neil J. Cornish
Date (v1): Fri, 15 Apr 2005 19:30:41 GMT (283kb)
Date (revised v2): Sat, 16 Apr 2005 19:01:28 GMT (179kb)
Characterizing the Galactic Gravitational Wave Background with LISA
Authors: Seth E. Timpano, Louis J. Rubbo, Neil J. Cornish
Comments: 29 pages, 12 figures
We present a Monte Carlo simulation for the response of the Laser
Interferometer Space Antenna (LISA) to the galactic gravitational wave
background. The simulated data streams are used to estimate the number and
type of binary systems that will be individually resolved. We find that the
background is highly non-Gaussian due to the presence of individual bright
sources, but once these sources are identified and removed, the remaining
signal is Gaussian. We give a new estimate of the confusion noise due to the
unresolved sources that differs significantly from earlier estimates.
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gr-qc/0506015
From: Neil J. Cornish
Date (v1): Fri, 3 Jun 2005 16:46:52 GMT (46kb)
Date (revised v2): Fri, 17 Jun 2005 04:35:37 GMT (46kb)
Date (revised v3): Mon, 17 Oct 2005 19:04:42 GMT (54kb)
Beyond LISA: Exploring Future Gravitational Wave Missions
Authors: Jeff Crowder, Neil J. Cornish
Comments: 9 pages, 10 figures, published version
Journal-ref: Phys.Rev. D72 (2005) 083005
The Advanced Laser Interferometer Antenna (ALIA) and the Big Bang Observer
(BBO) have been proposed as follow on missions to the Laser Interferometer
Space Antenna (LISA). Here we study the capabilities of these observatories,
and how they relate to the science goals of the missions. We find that the
Advanced Laser Interferometer Antenna in Stereo (ALIAS), our proposed
extension to the ALIA mission, will go considerably further toward meeting
ALIA's main scientific goal of studying intermediate mass black holes. We
also compare the capabilities of LISA to a related extension of the LISA
mission, the Laser Interferometer Space Antenna in Stereo (LISAS).
Additionally, we find that the initial deployment phase of the BBO would be
sufficient to address the BBO's key scientific goal of detecting the
Gravitational Wave Background, while still providing detailed information
about foreground sources.
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gr-qc/0506059
From: Neil J. Cornish
Date: Fri, 10 Jun 2005 19:51:28 GMT (196kb)
LISA Data Analysis using MCMC methods
Authors: Neil J. Cornish, Jeff Crowder
Comments: 14 pages, 7 figures
Journal-ref: Phys.Rev. D72 (2005) 043005
The Laser Interferometer Space Antenna (LISA) is expected to simultaneously
detect many thousands of low frequency gravitational wave signals. This
presents a data analysis challenge that is very different to the one
encountered in ground based gravitational wave astronomy. LISA data analysis
requires the identification of individual signals from a data stream
containing an unknown number of overlapping signals. Because of the signal
overlaps, a global fit to all the signals has to be performed in order to
avoid biasing the solution. However, performing such a global fit requires
the exploration of an enormous parameter space with a dimension upwards of
50,000. Markov Chain Monte Carlo (MCMC) methods offer a very promising
solution to the LISA data analysis problem. MCMC algorithms are able to
efficiently explore large parameter spaces, simultaneously providing
parameter estimates, error analyses and even model selection. Here we
present the first application of MCMC methods to simulated LISA data and
demonstrate the great potential of the MCMC approach. Our implementation
uses a generalized F-statistic to evaluate the likelihoods, and simulated
annealing to speed convergence of the Markov chains. As a final step we
super-cool the chains to extract maximum likelihood estimates, and estimates
of the Bayes factors for competing models. We find that the MCMC approach is
able to correctly identify the number of signals present, extract the source
parameters, and return error estimates consistent with Fisher information
matrix predictions.
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cond-mat/0501182
From: Craig M. Savage
Date: Mon, 10 Jan 2005 02:36:02 GMT (53kb)
Superradiant scattering from a hydrodynamic vortex
Authors: T.R. Slatyer, C.M. Savage
Comments: 10 pages, 1 figure
We show that sound waves scattered from a hydrodynamic vortex may be
amplified. Such superradiant scattering follows from the physical analogy
between spinning black holes and hydrodynamic vortices. However a sonic
horizon analogous to the black hole event horizon does not exist unless
the vortex possesses a central drain, which is challenging to produce
experimentally. In the astrophysical domain, superradiance can occur even
in the absence of an event horizon: we show that in the hydrodynamic
analogue, a drain is not required and a vortex scatters sound
superradiantly. Possible experimental realization in dilute gas Bose-
Einstein condensates is discussed.
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gr-qc/0508098
From: Andrew Moylan
Date: Wed, 24 Aug 2005 03:26:07 GMT (119kb)
Developments in GRworkbench
Authors: A. Moylan, S.M. Scott, A.C. Searle
Comments: 14 pages. To appear A. Moylan, S.M. Scott and A.C. Searle,
Developments in GRworkbench. Proceedings of the Tenth Marcel Grossmann
Meeting on General Relativity, editors M. Novello, S. Perez-Bergliaffa and
R. Ruffini. Singapore: World Scientific 2005
The software tool GRworkbench is an ongoing project in visual, numerical
General Relativity at The Australian National University. Recently,
GRworkbench has been significantly extended to facilitate numerical
experimentation in analytically-defined space-times. The numerical
differential geometric engine has been rewritten using functional
programming techniques, enabling objects which are normally defined as
functions in the formalism of differential geometry and General Relativity
to be directly represented as function variables in the C++ code of
GRworkbench. The new functional differential geometric engine allows for
more accurate and efficient visualisation of objects in space-times and
makes new, efficient computational techniques available. Motivated by the
desire to investigate a recent scientific claim using GRworkbench, new
tools for numerical experimentation have been implemented, allowing for
the simulation of complex physical situations.
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gr-qc/0412065
From: Francisco Lobo
Date: Tue, 14 Dec 2004 18:13:24 GMT (26kb)
Linearized warp drive and the energy conditions
Authors: Francisco S. N. Lobo, Matt Visser
Comments: 6 pages, contribution to the proceedings of the Spanish
Relativity Meeting-2004 (Miraflores de la Sierra, Madrid, September 2004)
"Warp drive" spacetimes are useful as "gedanken-experiments" and as a
theoretician's probe of the foundations of general relativity. Applying
linearized gravity to the weak-field warp drive, i.e., for non-relativistic
warp-bubble velocities, we find that the occurrence of energy condition
violations in this class of spacetimes is generic to the form of the
geometry under consideration and is not simply a side-effect of the
"superluminal" properties. Using the linearized construction it is now
possible to compare the warp field energy with the mass-energy of the
spaceship, and applying the "volume integral quantifier", extremely
stringent conditions on the warp drive spacetime are found.
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gr-qc/0503007
From: Matt Visser
Date: Wed, 2 Mar 2005 03:25:03 GMT (54kb)
Generating perfect fluid spheres in general relativity
Authors: Petarpa Boonserm, Matt Visser, Silke Weinfurtner
Comments: 18 pages, 4 tables, 4 figures
Ever since Karl Schwarzschild's 1916 discovery of the spacetime geometry
describing the interior of a particular idealized general relativistic star
-- a static spherically symmetric blob of fluid with position-independent
density -- the general relativity community has continued to devote
considerable time and energy to understanding the general-relativistic
static perfect fluid sphere. Over the last 90 years a tangle of specific
perfect fluid spheres has been discovered, with most of these specific
examples seemingly independent from each other. To bring some order to this
collection, in this article we develop several new transformation theorems
that map perfect fluid spheres into perfect fluid spheres. These
transformation theorems sometimes lead to unexpected connections between
previously known perfect fluid spheres, sometimes lead to new previously
unknown perfect fluid spheres, and in general can be used to develop a
systematic way of classifying the set of all perfect fluid spheres.
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gr-qc/0505065
From: Matt Visser
Date (v1): Fri, 13 May 2005 03:50:40 GMT (281kb)
Date (revised v2): Wed, 1 Jun 2005 00:16:05 GMT (362kb)
Analogue Gravity
Authors: Carlos Barcelo (IAA, Granada), Stefano Liberati (SISSA/ISAS,
Trieste), Matt Visser (Victoria University of Wellington)
Comments: V1: 151 pages; 12 figures; 427 references. This is a draft of a
"Living Review" that will shortly be submitted to the Journal "Living
Reviews in General Relativity". Constructive comments are welcome. V2: 152
pages, added 8 references and expanded discussion of a few technical points
Analogue models of (and for) gravity have a long and distinguished history
dating back to the earliest years of general relativity. In this review
article we will discuss the history, aims, results, and future prospects
for the various analogue models. We start the discussion by presenting a
particularly simple example of an analogue model, before exploring the rich
history and complex tapestry of models discussed in the literature. The
last decade in particular has seen a remarkable and sustained development
of analogue gravity ideas, leading to some hundreds of published articles,
a workshop, two books, and this review article. Future prospects for the
analogue gravity programme also look promising, both on the experimental
front (where technology is rapidly advancing) and on the theoretical front
(where variants of analogue models can be used as a springboard for radical
attacks on the problem of quantum gravity).
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gr-qc/0505137
From: Matt Visser
Date: Fri, 27 May 2005 02:36:51 GMT (21kb)
Gravastars must have anisotropic pressures
Authors: Celine Cattoen (Victoria University of Wellington), Tristan Faber
(Victoria University of Wellington), Matt Visser (Victoria University of
Wellington)
Comments: 15 pages; 4 figures; uses iopart.cls
One of the very small number of serious alternatives to the usual concept
of an astrophysical black hole is the "gravastar" model developed by Mazur
and Mottola; and a related phase-transition model due to Laughlin et al.
We consider a generalized class of similar models that exhibit continuous
pressure -- without the presence of infinitesimally thin shells. By
considering the usual TOV equation for static solutions with negative
central pressure, we find that gravastars cannot be perfect fluids --
anisotropic pressures in the "crust" of a gravastar-like object are
unavoidable. The anisotropic TOV equation can then be used to bound the
pressure anisotropy. The transverse stresses that support a gravastar
permit a higher compactness than is given by the Buchdahl--Bondi bound
for perfect fluid stars. Finally we comment on the qualitative features
of the equation of state that gravastar material must have if it is to do
the desired job of preventing horizon formation.
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gr-qc/0506029
From: Matt Visser
Date (v1): Mon, 6 Jun 2005 07:28:13 GMT (18kb)
Date (revised v2): Wed, 8 Jun 2005 08:48:39 GMT (18kb)
Massive Klein--Gordon equation from a BEC-based analogue spacetime
Authors: Matt Visser (Victoria University of Wellington), Silke Weinfurtner
(Victoria University of Wellington)
Comments: V1: 10 pages; uses revtex4; V2: two references and brief comments added
Journal-ref: Phys.Rev. D72 (2005) 044020
We extend the "analogue spacetime" programme by investigating a condensed-
matter system that is in principle capable of simulating the massive Klein
-Gordon equation in curved spacetime. Since many elementary particles have
mass, this is an essential step in building realistic analogue models, and
a first step towards simulating quantum gravity phenomenology. Specifically,
we consider the class of two-component BECs subject to laser-induced
transitions between the components. This system exhibits a complicated
spectrum of normal mode excitations, which can be viewed as two interacting
phonon modes that exhibit the phenomenon of "refringence". We study the
conditions required to make these two phonon modes decouple. Once decoupled,
the two distinct phonons generically couple to distinct effective
spacetimes, representing a bi-metric model, with one of the modes acquiring
a mass. In the eikonal limit the massive mode exhibits the dispersion
relation of a massive relativistic particle: omega = sqrt[omega_0^2 +
c^2 k^2], plus curved-space modifications. Furthermore, it is possible to
tune the system so that both modes can be arranged to travel at the same
speed, in which case the two phonon excitations couple to the same
effective metric. From the analogue spacetime perspective this situation
corresponds to the Einstein equivalence principle being satisfied.
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gr-qc/0508045
From: Matt Visser
Date (v1): Thu, 11 Aug 2005 04:49:42 GMT (16kb)
Date (revised v2): Tue, 30 Aug 2005 04:11:11 GMT (16kb)
Necessary and sufficient conditions for big bangs, bounces, crunches, rips,
sudden singularities, and extremality events
Authors: Celine Cattoen (Victoria University of Wellington), Matt Visser
(Victoria University of Wellington)
Comments: 20 pages, uses iopart.cls; several references added
Journal-ref: Class.Quant.Grav. 22 (2005) 4913-4930
The physically relevant singularities occurring in FRW cosmologies had
traditionally been thought to be limited to the "big bang", and possibly a
"big crunch". However, over the last few years, the zoo of cosmological
singularities considered in the literature has become considerably more
extensive, with "big rips" and "sudden singularities" added to the mix, as
well as renewed interest in non-singular cosmological events such as
"bounces" and "turnarounds". In this article we present a complete
catalogue of such cosmological milestones, both at the kinematical and
dynamical level. First, using generalized power series, purely kinematical
definitions of these cosmological events are provided in terms of the
behaviour of the scale factor a(t). The notion of a "scale-factor
singularity'" is defined, and its relation to curvature singularities
(polynomial and differential) is explored. Second, dynamical information
is extracted by using the Friedmann equations (without assuming even the
existence of any equation of state) to place constraints on whether or not
the classical energy conditions are satisfied at the cosmological
milestones. We use these considerations to derive necessary and sufficient
conditions for the existence of cosmological milestones such as bangs,
bounces, crunches, rips, sudden singularities, and extremality events.
Since the classification is extremely general, the corresponding results
are to a high degree model-independent: In particular, we provide a
complete characterization of the class of bangs, crunches, and sudden
singularities for which the dominant energy condition is satisfied.
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gr-qc/0510083
From: Matt Visser
Date (v1): Tue, 18 Oct 2005 03:10:58 GMT (20kb)
Date (revised v2): Wed, 26 Oct 2005 08:58:10 GMT (21kb)
Production and decay of evolving horizons
Authors: Matt Visser (Victoria University of Wellington), Alex B. Nielsen
(University of Canterbury)
Comments: 23 pages, uses iopart.cls V2: 5 references added; minor typos
We consider a simple physical model for an evolving horizon that is
strongly interacting with its environment, exchanging arbitrarily large
quantities of matter with its environment in the form of both infalling
material and outgoing Hawking radiation. We permit fluxes of both lightlike
and timelike particles to cross the horizon, and ask how the horizon grows
and shrinks in response to such flows. We place a premium on providing a
clear and straightforward exposition with simple formulae.
To be able to handle such a highly dynamical situation in a simple manner
we make one significant physical restriction, that of spherical symmetry,
and two technical mathematical restrictions: (1) We choose to slice the
spacetime in such a way that the space-time foliations (and hence the
horizons) are always spherically symmetric. (2) Furthermore we adopt
Painleve-Gullstrand coordinates (which are well suited to the problem
because they are nonsingular at the horizon) in order to simplify the
relevant calculations. We find particularly simple forms for surface
gravity, and for the first and second law of black hole thermodynamics,
in this general evolving horizon situation. Furthermore we relate our
results to Hawking's apparent horizon, Ashtekar's isolated and dynamical
horizons, and Hayward's trapping horizons. The evolving black hole model
discussed here will be of interest, both from an astrophysical viewpoint
in terms of discussing growing black holes, and from a purely theoretical
viewpoint in discussing black hole evaporation via Hawking radiation.
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gr-qc/0510125
From: Matt Visser
Date: Sun, 30 Oct 2005 06:28:37 GMT (34kb)
Analogue quantum gravity phenomenology from a two-component Bose-Einstein
condensate
Authors: Stefano Liberati (Sissa, Trieste and INFN, Italy), Matt Visser
(Victoria University of Wellington), Silke Weinfurtner (Victoria University
of Wellington)
Comments: 36 pages, uses iopart.sty
We present an analogue spacetime model that reproduces the salient features
of the most common ansatz for quantum gravity phenomenology. We do this by
investigating a system of two coupled Bose-Einstein condensates. This
system can be tuned to have two "phonon" modes (one massive, one massless)
which share the same limiting speed in the hydrodynamic approximation
[Phys. Rev. D72 (2005) 044020, gr-qc/0506029; cond-mat/0409639]. The system
nevertheless possesses (possibly non-universal) Lorentz violating terms at
very high energies where "quantum pressure" becomes important. We
investigate the physical interpretation of the relevant fine-tuning
conditions, and discuss the possible lessons and hints that this analogue
spacetime could provide for the phenomenology of real physical quantum
gravity. In particular we show that the effective field theory of quasi-
particles in such an emergent spacetime does not exhibit the so called
"naturalness problem".
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gr-qc/0511105
From: Silke Weinfurtner
Date: Fri, 18 Nov 2005 03:24:52 GMT (11kb)
Analogue model for quantum gravity phenomenology
Authors: Silke Weinfurtner, Stefano Liberati, Matt Visser
Comments: Talk given at 7th Workshop on Quantum Field Theory Under the
Influence of External Conditions (QFEXT 05), Barcelona, Catalonia, Spain,
5-9 Sep 2005
So called "analogue models" use condensed matter systems (typically
hydrodynamic) to set up an "effective metric" and to model curved-space
quantum field theory in a physical system where all the microscopic degrees
of freedom are well understood. Known analogue models typically lead to
massless minimally coupled scalar fields. We present an extended "analogue
space-time" programme by investigating a condensed-matter system - in and
beyond the hydrodynamic limit - that is in principle capable of simulating
the massive Klein-Gordon equation in curved spacetime. Since many elementary
particles have mass, this is an essential step in building realistic
analogue models, and an essential first step towards simulating quantum
gravity phenomenology. Specifically, we consider the class of two-component
BECs subject to laser-induced transitions between the components, and we
show that this model is an example for Lorentz invariance violation due to
ultraviolet physics. Furthermore our model suggests constraints on quantum
gravity phenomenology in terms of the "naturalness problem" and
"universality issue".
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hep-th/0502003
From: David Wiltshire
Date (v1): Tue, 1 Feb 2005 20:55:24 GMT (13kb)
Date (revised v2): Thu, 10 Feb 2005 20:45:52 GMT (14kb)
*Date (revised v3): Fri, 1 Jul 2005 13:25:34 GMT (14kb)
Accelerating cosmologies from compactification with a twist
Authors: Ishwaree P. Neupane, David L. Wiltshire
Comments: 5 pages, 1 figure, RevTeX4
Journal-ref: Phys.Lett. B619 (2005) 201
DOI: 10.1016/j.physletb.2005.06.008
It is demonstrated by explicit solutions of the (4+n)-dimensional vacuum
Einstein equations that accelerating cosmologies in the Einstein conformal
frame can be obtained by a time-dependent compactification of
string/M-theory, even in the case that internal dimensions are Ricci-flat,
provided one includes one or more geometric twists. Such acceleration is
transient. When both compact hyperbolic internal spaces and geometric
twists are included, however, the period of accelerated expansion may be
made arbitrarily large.
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gr-qc/0503099
From: David Wiltshire [view email]
Date (v1): Wed, 23 Mar 2005 10:22:03 GMT (14kb)
Date (revised v2): Thu, 24 Mar 2005 17:45:02 GMT (14kb)
Date (revised v3): Fri, 25 Mar 2005 04:13:08 GMT (15kb)
Date (revised v4): Wed, 6 Apr 2005 20:00:16 GMT (17kb)
Date (revised v5): Mon, 11 Jul 2005 11:22:10 GMT (19kb)
Viable inhomogeneous model universe without dark energy from primordial
inflation
Authors: David L. Wiltshire
Comments: 4 pages, aastex, emualteapj5.sty. v5: Complete overhaul of
notation and presentation to improve clarity. Corrected volume factor
increases age of universe
A new model of the observed universe, using solutions to the full Einstein
equations, is developed from the hypothesis that our observable universe is
an underdense bubble, with an internally inhomogeneous fractal bubble
distribution of bound matter systems, in a spatially flat bulk universe. It
is argued on the basis of primordial inflation and resulting structure
formation, that the clocks of the isotropic observers in average galaxies
coincide with clocks defined by the true surfaces of matter homogeneity of
the bulk universe, rather than the comoving clocks at average spatial
positions in the underdense bubble geometry, which are in voids. This
understanding requires a systematic reanalysis of all observed quantities
in cosmology. I begin such a reanalysis by giving a model of the average
geometry of the universe, which depends on two measured parameters: the
present matter density parameter, Omega_m, and the Hubble constant, H_0.
The observable universe is not accelerating. Nonetheless, inferred
luminosity distances are larger than naively expected, in accord with the
evidence of distant type Ia supernovae. The predicted age of the universe
is 15.3 +/-0.7 Gyr. The expansion age is larger than in competing models,
and may account for observed structure formation at large redshifts.
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astro-ph/0504192
From: David Wiltshire
Date (v1): Fri, 8 Apr 2005 10:57:51 GMT (68kb)
Date (revised v2): Tue, 12 Apr 2005 10:12:13 GMT (73kb)
Date (revised v3): Mon, 11 Jul 2005 11:35:25 GMT (71kb)
Type Ia supernovae tests of fractal bubble universe with no cosmic
acceleration
Authors: B.M.N. Carter, B.M. Leith, S.C.C. Ng, A.B. Nielsen, D.L. Wiltshire
Comments: 10 pages, 5 figures, aastex. v3: Corrected volume factor changes
parameter estimates and discussion, figures redrawn, references added
The unexpected dimness of Type Ia supernovae at redshifts z >~ 1 has over
the past 7 years been seen as an indication that the expansion of the
universe is accelerating. A new model cosmology, the "fractal bubble model",
has been proposed by one of us [gr-qc/0503099], based on the idea that our
observed universe resides in an underdense bubble remnant from a primordial
epoch of cosmic inflation, together with a new solution for averaging in an
inhomogeneous universe. Although there is no cosmic acceleration, it is
claimed that the luminosity distance of type Ia supernovae data will
nonetheless fit the new model, since it mimics a Milne universe at low
redshifts. In this paper the hypothesis is tested statistically against the
available type Ia supernovae data by both chi-square and Bayesian methods.
While the standard model with cosmological constant Omega_Lambda = 1-Omega_m
is favoured by a Bayesian analysis with wide priors, the comparison depends
strongly on the priors chosen for the density parameter, Omega_m. The
fractal bubble model gives better agreement generally for Omega_m<0.2. It
also gives reasonably good fits for all the range, Omega_m=0.01-0.55,
allowing the possibility of a viable cosmology with just baryonic matter, or
alternatively with both baryonic matter and additional cold dark matter.
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hep-th/0504135
From: Ishwaree P. Neupane
Date (v1): Mon, 18 Apr 2005 19:46:35 GMT (92kb)
Date (revised v2): Wed, 27 Apr 2005 19:49:15 GMT (93kb)
Cosmic Acceleration from M Theory on Twisted Spaces
Authors: Ishwaree P. Neupane, David L. Wiltshire
Comments: 16 pages, 2 figures, RevTex4; references added
In a recent paper [hep-th/0502003] we have found a new class of accelerating
cosmologies arising from time-dependent compactifications of classical
supergravities on product spaces that include one or more geometric twists
along with non-trivial curved internal spaces. With such effects, a scalar
potential can have a locally stable minimum with positive vacuum energy. The
existence of such a minimum generically predicts a period of accelerated
expansion in the four-dimensional conformal frame. Here we considerably
extend our knowledge of these solutions by presenting more new examples, and
discuss their properties in a more general setting, which relates the
solutions to other types of solutions with simple product spaces for
internal manifolds.
******************************************************************************
ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc,
December 2004 - November 2005
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/0412022
From: John T. Whelan
Date: Sat, 4 Dec 2004 22:12:56 GMT (16kb)
First upper limit analysis and results from LIGO science data: stochastic
background
Authors: John T. Whelan, for the LIGO Scientific Collaboration
Comments: 7 pages; 1 eps figures; proceeding from 2003 Edoardo Amaldi
Meeting on Gravitational Waves
Journal-ref: Class.Quant.Grav. 21 (2004) 685-690
I describe analysis of correlations in the outputs of the three LIGO
interferometers from LIGO's first science run, held over 17 days in August
and September of 2002, and the resulting upper limit set on a stochastic
background of gravitational waves. By searching for cross-correlations
between the LIGO detectors in Livingston, LA and Hanford, WA, we are able
to set a 90% confidence level upper limit of h_{100}^2 Omega_0 < 23 +/- 4.6.
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gr-qc/0501068
From: Szabolcs M\'arka
Date (v1): Mon, 24 Jan 2005 03:25:30 GMT (357kb)
Date (revised v2): Sun, 20 Feb 2005 21:22:15 GMT (357kb)
A Search for Gravitational Waves Associated with the Gamma Ray Burst
GRB030329 Using the LIGO Detectors
Authors: The LIGO Scientific Collaboration
Comments: 18 pages, 9 figures and 3 tables; Minor Updates: Authorlist,
Acknowledgement; Added: Ref [65]
Report-no: LIGO-P040007-07-D
We have performed a search for bursts of gravitational waves associated with
the very bright Gamma Ray Burst GRB030329, using the two detectors at the
LIGO Hanford Observatory. Our search covered the most sensitive frequency
range of the LIGO detectors (approximately 80-2048 Hz), and we specifically
targeted signals shorter than 150 ms. Our search algorithm looks for excess
correlated power between the two interferometers and thus makes minimal
assumptions about the gravitational waveform. We observed no candidates with
gravitational wave signal strength larger than a pre-determined threshold.
We report frequency dependent upper limits on the strength of the
gravitational waves associated with GRB030329. Near the most sensitive
frequency region, around 250 Hz, our root-sum-square (RSS) gravitational
wave strain sensitivity for optimally polarized bursts was better than
h_RSS = 6E-21 Hz^{-1/2}. Our result is comparable to the best published
results searching for association between gravitational waves and GRBs.
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gr-qc/0504065
From: Eirini Messaritaki
Date: Thu, 14 Apr 2005 19:07:56 GMT (886kb)
Report on the first binary black hole inspiral search in LIGO data
Authors: Eirini Messaritaki, for the LIGO Scientific Collaboration
Comments: 10 pages, 2 figures, submitted to CQG for inclusion in the GWDAW9
proceedings
The LIGO Scientific Collaboration is currently engaged in the first search
for binary black hole inspiral signals in real data. We are using the data
from the second LIGO science run and we focus on inspiral signals coming
from binary systems with component masses between 3 and 20 solar masses. We
describe the analysis methods used and report on preliminary estimates for
the sensitivities of the LIGO instruments during the second science run.
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gr-qc/0504067
From: Nelson Christensen
Date: Fri, 15 Apr 2005 11:28:16 GMT (298kb)
Veto Studies for LIGO Inspiral Triggers
Authors: Nelson Christensen (for the LIGO Scientific Collaboration)
Comments: Submitted to Classical and Quantum Gravity for the special issue
for presentations at GWDAW 9
LIGO recently conducted its third scientific data run, S3. Here we summarize
the veto and data quality studies conducted by the LIGO Scientific
Collaboration in connection with the search for binary inspiral signals in
the S3 data. LIGO's interferometer channels and physical environmental
monitors were monitored, and events in these channels coincident with
inspiral triggers were examined.
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gr-qc/0504106
From: Alessandra Di Credico
Date: Thu, 21 Apr 2005 16:39:21 GMT (243kb)
Gravitational wave burst vetoes in the LIGO S2 and S3 data analyses
Authors: Alessandra Di Credico (for the LIGO Scientific Collaboration)
Comments: 9 pages, 4 figures, submitted to Classical and Quantum Gravity for
the special issue of the GWDAW9 Proceedings
The LIGO detectors collected about 4 months of data in 2003-2004 during two
science runs, S2 and S3. Several environmental and auxiliary channels that
monitor the instruments' physical environment and overall interferometric
operation were analyzed in order to establish the quality of the data as
well as the presence of transients of non-astrophysical origin. This
analysis allowed better understanding of the noise character of the
instruments and the establishment of correlations between transients in
these channels and the one recording the gravitational wave strain. In this
way vetoes for spurious burst were identified. We present the methodology we
followed in this analysis and the results from the S2 and S3 veto analysis
within the context of the search for gravitational wave bursts.
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gr-qc/0504128
From: Hirotaka Takahashi
Date: Tue, 26 Apr 2005 01:28:38 GMT (111kb)
Status of the joint LIGO--TAMA300 inspiral analysis
Authors: Stephen Fairhurst, for the LIGO Scientific Collaboration, Hirotaka
Takahashi, for the TAMA Collaboration
Comments: 10 page, 8 figures, submitted to Classical and Quantum Gravity for
the special issue of the GWDAW9 Proceedings
Report-no: OU-TAP 257
We present the status of the joint search for gravitational waves from
inspiraling neutron star binaries in the LIGO Science Run 2 and TAMA300 Data
Taking Run 8 data, which was taken from February 14 to April 14, 2003, by
the LIGO and TAMA collaborations. In this paper we discuss what has been
learned from an analysis of a subset of the data sample reserved as a
"playground". We determine the coincidence conditions for parameters such as
the coalescence time and chirp mass by injecting simulated Galactic binary
neutron star signals into the data stream. We select coincidence conditions
so as to maximize our efficiency of detecting simulated signals. We obtain
an efficiency for our coincident search of 78 %, and show that we are
missing primarily very distant signals for TAMA300. We perform a time slide
analysis to estimate the background due to accidental coincidence of noise
triggers. We find that the background triggers have a very different
character from the triggers of simulated signals.
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gr-qc/0505029
From: E Katsavounidis
Date: Fri, 6 May 2005 18:08:54 GMT (158kb)
Upper limits on gravitational wave bursts in LIGO's second science run
Authors: LIGO Scientific Collaboration
Comments: 23 pages, 14 figures, to be submitted to Phys Rev D
Report-no: LIGO Laboratory document P-040040-07-R
We perform a search for gravitational wave bursts using data from the second
science run of the LIGO detectors, using a method based on a wavelet time-
frequency decomposition. This search is sensitive to bursts of duration much
less than a second and with frequency content in the 100-1100Hz range. It
features significant improvements in the instrument sensitivity and in the
analysis pipeline with respect to the burst search previously reported by
LIGO. Improvements in the search method allow exploring weaker signals,
relative to the detector noise floor, while maintaining a low false alarm
rate, O(0.1) microHz. The sensitivity in terms of the root-sum-square (rss)
strain amplitude lies in the range of hrss~10^{-20} - 10^{-19}/sqrt(Hz) No
gravitational wave signals were detected in 9.98 days of analyzed data. We
interpret the search result in terms of a frequentist upper limit on the
rate of detectable gravitational wave bursts at the level of 0.26 events per
day at 90% confidence level. We combine this limit with measurements of the
detection efficiency for given waveform morphologies in order to yield rate
versus strength exclusion curves as well as to establish order-of-magnitude
distance sensitivity to certain modeled astrophysical sources. Both the rate
upper limit and its applicability to signal strengths improve our previously
reported limits and reflect the most sensitive broad-band search for
untriggered and unmodeled gravitational wave bursts to date.
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gr-qc/0505041
From: Gabriela Gonz\'alez
Date (v1): Tue, 10 May 2005 02:36:47 GMT (439kb)
Date (revised v2): Thu, 12 May 2005 19:13:54 GMT (439kb)
Search for gravitational waves from galactic and extra--galactic binary
neutron stars
Authors: LIGO Scientific Collaboration: B. Abbott, et al
Comments: 20 pages, 12 figures, to be submitted to Phys. Rev. D
Report-no: LIGO-P040024-04-Z
We use 373 hours ($\approx$ 15 days) of data from the second science run of
the LIGO gravitational-wave detectors to search for signals from binary
neutron star coalescences within a maximum distance of about 1.5 Mpc, a
volume of space which includes the Andromeda Galaxy and other galaxies of
the Local Group of galaxies. This analysis requires a signal to be found in
data from detectors at the two LIGO sites, according to a set of coincidence
criteria. The background (accidental coincidence rate) is determined from
the data and is used to judge the significance of event candidates. No
inspiral gravitational wave events were identified in our search. Using a
population model which includes the Local Group, we establish an upper limit
of less than 47 inspiral events per year per Milky Way equivalent galaxy
with 90% confidence for non-spinning binary neutron star systems with
component masses between 1 and 3 $M_\odot$.
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gr-qc/0505042
From: Duncan Brown
Date: Tue, 10 May 2005 02:37:19 GMT (175kb)
Search for Gravitational Waves from Primordial Black Hole Binary
Coalescences in the Galactic Halo
Authors: LIGO Scientific Collaboration: B. Abbott, et al
Comments: 7 pages, 4 figures, to be submitted to Phys. Rev. D
Report-no: LIGO-P040045-04-Z
We use data from the second science run of the LIGO gravitational-wave
detectors to search for the gravitational waves from primordial black hole
(PBH) binary coalescence with component masses in the range 0.2--$1.0
M_\odot$. The analysis requires a signal to be found in the data from both
LIGO observatories, according to a set of coincidence criteria. No inspiral
signals were found. Assuming a spherical halo with core radius 5 kpc
extending to 50 kpc containing non-spinning black holes with masses in the
range 0.2--$1.0 M_\odot$, we place an observational upper limit on the rate
of PBH coalescence of 63 per year per Milky Way halo (MWH) with 90%
confidence.
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gr-qc/0505076
From: Matthew Pitkin
Date: Mon, 16 May 2005 11:42:51 GMT (62kb)
Searching for gravitational waves from known pulsars
Authors: Matthew Pitkin, for the LIGO Scientific Collaboration
Comments: Accepted by CQG for the proceeding of GWDAW9, 7 pages, 2 figures
We present upper limits on the amplitude of gravitational waves from 28
isolated pulsars using data from the second science run of LIGO. The results
are also expressed as a constraint on the pulsars' equatorial ellipticities.
We discuss a new way of presenting such ellipticity upper limits that takes
account of the uncertainties of the pulsar moment of inertia. We also extend
our previous method to search for known pulsars in binary systems, of which
there are about 80 in the sensitive frequency range of LIGO and GEO 600.
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gr-qc/0505102
From: Duncan Brown
Date: Thu, 19 May 2005 23:45:55 GMT (40kb)
Using the INSPIRAL program to search for gravitational waves from low-mass
binary inspiral
Authors: Duncan A Brown (for the LIGO Scientific Collaboration)
Comments: 11 pages, 3 figures, submitted to Classical and Quantum Gravity
for the special issue of the GWDAW9 Proceedings
The INSPIRAL program is the LIGO Scientific Collaboration's computational
engine for the search for gravitational waves from binary neutron stars
and sub-solar mass black holes. We describe how this program, which makes
use of the FINDCHIRP algorithm (discussed in a companion paper), is
integrated into a sophisticated data analysis pipeline that was used in the
search for low-mass binary inspirals in data taken during the second LIGO
science run.
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gr-qc/0507081
From: Patrick Sutton
Date (v1): Tue, 19 Jul 2005 01:43:57 GMT (389kb)
Date (revised v2): Wed, 20 Jul 2005 00:37:41 GMT (351kb)
Date (revised v3): Tue, 26 Jul 2005 17:49:15 GMT (318kb)
Upper limits from the LIGO and TAMA detectors on the rate of gravitational-
wave bursts
Authors: LIGO Scientific Collaboration, TAMA Collaboration
Comments: 15 pages, 11 figures, to be submitted to Phys Rev D. Updated
author list
Report-no: LIGO-P040050-06-Z
We report on the first joint search for gravitational waves by the TAMA and
LIGO collaborations. We looked for millisecond-duration unmodelled
gravitational-wave bursts in 473 hr of coincident data collected during
early 2003. No candidate signals were found. We set an upper limit of
0.12 events per day on the rate of detectable gravitational-wave bursts,
at 90% confidence level. From simulations, we estimate that our detector
network was sensitive to bursts with root-sum-square strain amplitude
above approximately 1-3x10^{-19} Hz^{-1/2} in the frequency band 700-2000
Hz. We describe the details of this collaborative search, with particular
emphasis on its advantages and disadvantages compared to searches by LIGO
and TAMA separately using the same data. Benefits include a lower
background and longer observation time, at some cost in sensitivity and
bandwidth. We also demonstrate techniques for performing coincidence
searches with a heterogeneous network of detectors with different noise
spectra and orientations. These techniques include using coordinated signal
injections to estimate the network sensitivity, and tuning the analysis to
maximize the sensitivity and the livetime, subject to constraints on the
background.
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astro-ph/0507254
From: Joseph Romano
Date: Mon, 11 Jul 2005 13:53:52 GMT (139kb)
Upper Limits on a Stochastic Background of Gravitational Waves
Authors: LIGO Scientific Collaboration: B. Abbott, et al
Comments: 6 pages, 4 figures
The Laser Interferometer Gravitational Wave Observatory (LIGO) has
performed a third science run with much improved sensitivities of all
three interferometers. We present an analysis of approximately 200 hours
of data acquired during this run, used to search for a stochastic
background of gravitational radiation. We place upper bounds on the energy
density stored as gravitational radiation for three different spectral
power laws. For the flat spectrum, our limit of Omega_0<8.4e-4 in the
69-156 Hz band is ~10^5 times lower than the previous result in this
frequency range.
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gr-qc/0508065
From: Alicia M. Sintes
Date: Tue, 16 Aug 2005 09:22:26 GMT (863kb)
First all-sky upper limits from LIGO on the strength of periodic
gravitational waves using the Hough transform
Authors: LIGO Scientific Collaboration: B. Abbott, et al
Comments: 22 pages, 21 figures, to be submitted to Phys. Rev. D
Report-no: LIGO-P050013-03-R
We perform a wide parameter space search for continuous gravitational waves
over the whole sky and over a large range of values of the frequency and
the first spin-down parameter. Our search method is based on the Hough
transform, which is a semi-coherent, computationally efficient, and robust
pattern recognition technique. We apply this technique to data from the
second science run of the LIGO detectors and our final results are all-sky
upper limits on the strength of gravitational waves emitted by unknown
isolated spinning neutron stars on a set of narrow frequency bands in the
range 200-$400 $Hz. The best upper limit on the gravitational wave strain
amplitude that we obtain in this frequency range is $4.43\times 10^{-23}$.
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gr-qc/0509129
From: Eirini Messaritaki
Date: Fri, 30 Sep 2005 17:08:23 GMT (528kb)
Search for gravitational waves from binary black hole inspirals in LIGO
data
Authors: LIGO Scientific Collaboration: B. Abbott et. al
Comments: 18 pages, 8 figures
We report on a search for gravitational waves from binary black hole
inspirals in the data from the second science run of the LIGO
interferometers. The search focused on binary systems with component masses
between 3 and 20 solar masses. Optimally oriented binaries with distances
up to 1 Mpc could be detected with efficiency of at least 90%. We found no
events that could be identified as gravitational waves in the 385.6 hours
of data that we searched.
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gr-qc/0511146
From: Lindy Blackburn
Date: Sun, 27 Nov 2005 22:13:06 GMT (400kb)
Search for gravitational wave bursts in LIGO's third science run
Authors: LIGO Scientific Collaboration
Comments: 12 pages, 6 figures. Amaldi-6 conference proceedings to be
published in Classical and Quantum Gravity
Report-no: P050043-A-R
We report on a search for gravitational wave bursts in data from the
three LIGO interferometric detectors during their third science run. The
search targets subsecond bursts in the frequency range 100-1100 Hz for
which no waveform model is assumed, and has a sensitivity in terms of the
root-sum-square (rss) strain amplitude of hrss ~ 10^{-20} / sqrt(Hz). No
gravitational wave signals were detected in the 8 days of analyzed data.
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