Subject: ASGRG Newsletter #18
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AUSTRALASIAN SOCIETY FOR GENERAL RELATIVITY AND GRAVITATION
Electronic Newsletter -- #18, 2008
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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, 2009.
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CONTENTS:
* REPORT ON AMSI WORKSHOP ON MATHEMATICAL GENERAL RELATIVITY
* MEMBERSHIP DETAILS ONLINE at
http://www.physics.adelaide.edu.au/ASGRG/members.html
* SUBSCRIPTIONS
* FORTHCOMING MEETINGS
* MEMBERS' ABSTRACTS at gr-qc, December 2007 - November 2008
* ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc,
December 2007 - November 2008
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Report on AMSI Workshop
on Mathematical General Relativity
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AMSI WORKSHOP ON MATHEMATICAL RELATIVITY:
UNIVERSITY OF MELBOURNE, 7-9 JULY 2007
A 3-day Workshop on mathematical general relativity was held in the
Australian Mathematical Sciences Institute (AMSI) Building on the
Melbourne University campus in July. The Workshop was organised by
Con Lozanovski of Swinburne Institute of Technology, who single-
handedly drafted an impressive line-up of invited speakers and
coaxed generous sponsorship from the AMSI, the ASGRG, Swinburne
and software suppliers Analytica.
The keynote speakers were:
* Joerg Frauendiener of the University of Otago, who spoke about
the relativistic theory of elasticity in the limit of static spherical
symmetry,
* Susan Scott of the Australian National University, who spoke
about the application of conformal structures to future cosmological
singularities,
* Todd Oliynyk, who spoke about second-order Newtonian expansions
for perfect fluids,
* Matthew Choptuik of the University of British Columbia, who spoke
about numerical tests of the cosmic censorship conjecture,
* Robert Bartnik of Monash University, who spoke about geometric
boundary conditions for the Ricci tensor,
* Edward Fackerell of the University of Sydney, who spoke on the
1-Killing-vector vacuum Einstein equations,
* Peter Szekeres of the University of Adelaide, who spoke about
conformal gravity and the variation of fundamental constants, and
* Pengzi Miao of Monash University, who spoke about the first
variation of quasi-local mass.
The other contributing speakers were Chris Goddard (Melbourne), Celine
Cattoen (Wellington), Gabriel Abreu (Wellington), Petarpa Boonserm
(Weliington), Florian Beyer (Albert Einstein Institute), Leo Brewin
(Monash), Jules Katjar (Monash), Malcolm Anderson (Brunei) and
Con Lozanovski (Swinburne). Celine Cattoen won the prize for the best
student presentation, and was awarded a copy of Roger Penrose's "The
Road to Reality".
The weather in Melbourne during the workshop was unfortunately cold
and wet, but we were compensated with a superb conference dinner
at the Brandon Hotel in Carlton North on July 8 (all free courtesy of
the sponsors). Warm thanks to Con Lozanovski for hosting such an
enjoyable metting.
Malcolm Anderson
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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 2009 - June 2010 subscriptions are requested, if you wish to
pay for July 2010 - June 2011 at the same time, it may simplify matters.
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FORTHCOMING MEETINGS
February 24-27, 2009: 3rd High-Frequency Gravitational Wave Workshop (HFGW3)
Von Braun Center, Huntsville, Alabama, USA
http://www.maths.qmul.ac.uk/hyperspace/conference/08May.9.html
April 13-17, 2009: Grav 09
Hotel del Lago - La Falda, Cordoba, Argentina
httP://www.famaf.unc.edu.ar/~gdotti/grg/grav09/grav09.htm
April 27 - May 1, 2009: IAU Symposium 261
"Relativity in Fundamental Astronomy: Dynamics, Reference Frames
and Fundamental Astronomy"
Cavalier Hotel, Virginia Beach, Virginia, USA
http://www.aas.org/divisions/meetings/iau/
May 25-30, 2009: APCTP-BLTP JINR Joint Workshop
"Frontiers in Black Hole Physics at Dubna"
Dubna, Russia
http://fbhp.jinr.ru/
June 4-5, 2009: Ecole Internationale Daniel Chalonge
"Physics of the Standard Model of the Universe:
Theory and Observations"
Cite Internationale Universitaire de Paris, Paris, France
http://chalonge.obspm.fr/colloque_ES2009.html
June 18-19, 2009: Mathematical Relativity in Lisbon
Instituto Superior Tecnico, Lisbon, Portugal
http://www.math.ist.utl.pt/~jnatar/Mira/
June 28 - July 2, 2009: IX Asia-Pacific Conference on Gravitation and Astrophysics (ICGA9)
Huazhong university of Science and Technology, Wuhan, China
http://ggg.hust.edu.cn/ICGA9/icga9.htm
June 29 - July 1, 2009: The Unity of the Universe
Institute of Cosmology and Gravitation, University of Portsmouth, UK
http://www.icg.port.ac.uk/sciama09/
June 29 - July 3, 2009: Invisible Universe
UNESCO Headquarters, Paris, France
http://www.universe2009.obspm.fr/
July 12-18, 2009: 12th Marcel Grossman Meeting on General Relativity
UNESCO Headquarters, Paris, France
http://www.icra.it/MG/mg12/en/
September 14-19, 2009: Grassmannian Conference in Fundamental Cosmology
University of Szczeczin, Szczeczin, Poland
http://cosmo.fiz.univ.szczecin.pl/
October 26-30, 2009: First Galileo-Xu Guangqi Meeting
"The Sun, the Stars, the Universe and General Relativity"
Shanghai, China
http://www.icranet.org/index.php/
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MEMBERS' ABSTRACTS at gr-qc, December 2007 - November 2008
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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arXiv:0802.3332v2
Searching for gravitational waves from Cassiopeia A with LIGO
Authors: K. Wette, B. J. Owen, B. Allen, M. Ashley, J. Betzwieser,
N. Christensen, T. D. Creighton, V. Dergachev, I. Gholami, E. Goetz,
R. Gustafson, D. Hammer, D. I. Jones, B. Krishnan, M. Landry,
B. Machenschalk, D. E. McClelland, G. Mendell, C. J. Messenger,
M. A. Papa, P. Patel, M. Pitkin, H. J. Pletsch, R. Prix, K. Riles,
L. Sancho de la Jordana, S. M. Scott, A. M. Sintes, M. Trias,
J. T. Whelan, G. Woan
(Submitted on 22 Feb 2008 (v1), last revised 8 Oct 2008 (this version, v2))
8 pages, 1 figure
We describe a search underway for periodic gravitational waves from the
central compact object in the supernova remnant Cassiopeia A. The object
is the youngest likely neutron star in the Galaxy. Its position is well
known, but the object does not pulse in any electromagnetic radiation
band and thus presents a challenge in searching the parameter space of
frequency and frequency derivatives. We estimate that a fully coherent
search can, with a reasonable amount of time on a computing cluster,
achieve a sensitivity at which it is theoretically possible (though not
likely) to observe a signal even with the initial LIGO noise spectrum.
Cassiopeia A is only the second object after the Crab pulsar for which
this is true. The search method described here can also obtain interesting
results for similar objects with current LIGO sensitivity.
Journal reference: Class. Quantum Grav. 25 235011 (2008)
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arXiv:0802.3263v1
Quadratic superconducting cosmic strings revisited
Authors: Mustapha Azreg-Aďnou
(Submitted on 22 Feb 2008)
6 pages
It has been shown that 5-dimensional general relativity action extended
by appropriate quadratic terms admits a singular superconducting cosmic
string solution. We search for cosmic strings endowed with similar and
extended physical properties by directly integrating the non-linear
matrix field equations thus avoiding the perturbative approach by which
we constructed the above-mentioned \textsl{exact} solution. The most
general superconducting cosmic string, subject to some constraints, will
be derived and shown to be mathematically \textsl{unique} up to linear
coordinate transformations mixing its Killing vectors. The most general
solution, however, is not globally equivalent to the old one due to the
existence of Killing vectors with closed orbits.
Journal reference: Europhys.Lett.81:60003,2008
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arXiv:0801.1150v1
Observation of Three Mode Parametric Interactions in Long Optical Cavities
Authors: C. Zhao, L. Ju, Y. Fan, S. Gras. B. J. J. Slagmolen, H. Miao,
P. Barriga D.G. Blair, D. J. Hosken, A. F. Brooks, P. J. Veitch, D. Mudge,
J. Munch
(Submitted on 8 Jan 2008)
10 pages and 5 figures
We report the first observation of three-mode opto-acoustic parametric
interactions of the type predicted to cause parametric instabilities in
an 80 m long, high optical power cavity that uses suspended sapphire
mirrors. Resonant interaction occurs between two distinct optical modes
and an acoustic mode of one mirror when the difference in frequency
between the two optical cavity modes is close to the frequency of the
acoustic mode. Experimental results validate the theory of parametric
instability in high power optical cavities.
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arXiv:0802.0582v1 [astro-ph]
Astrodynamical Space Test of Relativity using Optical Devices I (ASTROD I)
- A class-M fundamental physics mission proposal for Cosmic Vision 2015-2025
Authors: Thierry Appourchaux, Raymond Burston, Yanbei Chen, Michael Cruise,
Hansjoerg Dittus, Bernard Foulon, Patrick Gill, Laurent Gizon, Hugh Klein,
Sergei Klioner, Sergei Kopeikin, Hans Krueger, Claus Laemmerzahl,
Alberto Lobo, Xinlian Luo, Helen Margolis, Wei-Tou Ni, Antonio Pulido Paton,
Qiuhe Peng, Achim Peters, Ernst Rasel, Albrecht Ruediger, Etienne Samain,
Hanns Selig, Diana Shaul, Timothy Sumner, Stephan Theil, Pierre Touboul,
Slava Turyshev, Haitao Wang, Li Wang, Linqing Wen, Andreas Wicht, Ji Wu,
Xiaomin Zhang, Cheng Zhao
(Submitted on 5 Feb 2008)
26 pages, 11 figures, shortened from the original cosmic vision proposal,
submitted to Experimental Astronomy
ASTROD I is a planned interplanetary space mission with multiple goals.
The primary aims are: to test General Relativity with an improvement in
sensitivity of over 3 orders of magnitude, improving our understanding
of gravity and aiding the development of a new quantum gravity theory;
to measure key solar system parameters with increased accuracy, advancing
solar physics and our knowledge of the solar system and to measure the
time rate of change of the gravitational constant with an order of
magnitude improvement and the anomalous Pioneer acceleration, thereby
probing dark matter and dark energy gravitationally. It is an international
project, with major contributions from Europe and China and is envisaged
as the first in a series of ASTROD missions. ASTROD I will consist of one
spacecraft carrying a telescope, four lasers, two event timers and a clock.
Two-way, two-wavelength laser pulse ranging will be used between the
spacecraft in a solar orbit and deep space laser stations on Earth, to
achieve the ASTROD I goals. A second mission, ASTROD II is envisaged as
a three-spacecraft mission which would test General Relativity to one
part per billion, enable detection of solar g-modes, measure the solar
Lense-Thirring effect to 10 parts per million, and probe gravitational
waves at frequencies below the LISA bandwidth. In the third phase (ASTROD
III or Super-ASTROD), larger orbits could be implemented to map the outer
solar system and to probe primordial gravitational-waves at frequencies
below the ASTROD II bandwidth.
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arXiv:0804.0332v1
The Effect of Higher Harmonic Corrections on the Detection of massive
black hole binaries with LISA
Authors: Edward K. Porter, Neil J. Cornish
(Submitted on 2 Apr 2008)
15 pages, 8 figures, submitted to PRD
Massive black hole binaries are key targets for the space based
gravitational wave interferometer LISA. Several studies have
investigated how LISA observations could be used to constrain the
parameters of these systems. Until recently, most of these studies
have ignored the higher harmonic corrections to the waveforms. Here we
analyze the effects of the higher harmonics in more detail by performing
extensive Monte Carlo simulations. We pay particular attention to how
the higher harmonics impact parameter correlations, and show that the
additional harmonics help mitigate the impact of having two laser links
fail, by allowing for an instantaneous measurement of the gravitational
wave polarization with a single interferometer channel. By looking at
parameter correlations we are able to explain why certain mass ratios
provide dramatic improvements in certain parameter estimations, and
illustrate how the improved polarization measurement improves the
prospects for single interferometer operation.
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arXiv:0804.3323v2
Detection Strategies for Extreme Mass Ratio Inspirals
Authors: N. J. Cornish
(Submitted on 21 Apr 2008 (v1), last revised 5 Aug 2008 (this version, v2))
6 pages, 4 figures
The capture of compact stellar remnants by galactic black holes provides
a unique laboratory for exploring the near horizon geometry of the Kerr
spacetime, or possible departures from general relativity if the central
cores prove not to be black holes. The gravitational radiation produced
by these Extreme Mass Ratio Inspirals (EMRIs) encodes a detailed map of
the black hole geometry, and the detection and characterization of these
signals is a major scientific goal for the LISA mission. The waveforms
produced are very complex, and the signals need to be coherently tracked
for hundreds to thousands of cycles to produce a detection, making EMRI
signals one of the most challenging data analysis problems in all of
gravitational wave astronomy. Estimates for the number of templates
required to perform an exhaustive grid-based matched-filter search for
these signals are astronomically large, and far out of reach of current
computational resources. Here a hierarchical approach to the EMRI detection
problem is developed that employs a directed-stochastic search technique.
The algorithm, dubbed Metropolis Hastings Monte Carlo (MHMC), is closely
related to Markov Chain Monte Carlo and genetic algorithms. The utility
of the MHMC approach is demonstrated using simulated data sets from the
Mock LISA Data Challenge.
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arXiv:0806.2110v1
The Mock LISA Data Challenges: from Challenge 1B to Challenge 3
Authors: Stanislav Babak, John G. Baker, Matthew J. Benacquista,
Neil J. Cornish, Jeff Crowder, Shane L. Larson, Eric Plagnol,
Edward K. Porter, Michele Vallisneri, Alberto Vecchio (the Mock LISA
Data Challenge Task Force), Keith Arnaud, Leor Barack, Arkadiusz Blaut,
Curt Cutler, Stephen Fairhurst, Jonathan Gair, Xuefei Gong, Ian Harry,
Deepak Khurana, Andrzej Królak, Ilya Mandel, Reinhard Prix,
B. S. Sathyaprakash, Pavlin Savov, Yu Shang, Miquel Trias, John Veitch,
Yan Wang, Linqing Wen, John T. Whelan (the Challenge 1B participants)
(Submitted on 12 Jun 2008)
20 pages, 3 EPS figures. Proceedings of the 12th Gravitational Wave
Data Analysis Workshop, Cambridge MA, 13--16 December 2007
The Mock LISA Data Challenges are a programme to demonstrate and encourage
the development of LISA data-analysis capabilities, tools and techniques.
At the time of this workshop, three rounds of challenges had been completed,
and the next was about to start. In this article we provide a critical
analysis of entries to the latest completed round, Challenge 1B. The
entries confirm the consolidation of a range of data-analysis techniques
for Galactic and massive--black-hole binaries, and they include the first
convincing examples of detection and parameter estimation of extreme-mass
-ratio inspiral sources. In this article we also introduce the next round,
Challenge 3. Its data sets feature more realistic waveform models (e.g.,
Galactic binaries may now chirp, and massive--black-hole binaries may
precess due to spin interactions), as well as new source classes (bursts
from cosmic strings, isotropic stochastic backgrounds) and more
complicated nonsymmetric instrument noise.
Journal reference: Class.Quant.Grav.25:184026,2008
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arXiv:0811.1011v1
Massive Black Hole Binary Inspirals: Results from the LISA Parameter
Estimation Taskforce
Authors: K. G. Arun, Stas Babak, Emanuele Berti, Neil Cornish, Curt Cutler,
Jonathan Gair, Scott A. Hughes, Bala R. Iyer, Ryan N. Lang, Ilya Mandel,
Edward K. Porter, Bangalore S. Sathyaprakash, Siddhartha Sinha,
Alicia M. Sintes, Miquel Trias, Chris Van Den Broeck, Marta Volonteri
(Submitted on 6 Nov 2008)
14 pages, 2 figures, 5 tables, submitted to proceedings of 7th LISA
Symposium.
The LISA Parameter Estimation (LISAPE) Taskforce was formed in September
2007 to provide the LISA Project with vetted codes, source distribution
models, and results related to parameter estimation. The Taskforce's goal
is to be able to quickly calculate the impact of any mission design
changes on LISA's science capabilities, based on reasonable estimates of
the distribution of astrophysical sources in the universe. This paper
describes our Taskforce's work on massive black-hole binaries (MBHBs).
Given present uncertainties in the formation history of MBHBs, we adopt
four different population models, based on (i) whether the initial black-
hole seeds are small or large, and (ii) whether accretion is efficient or
inefficient at spinning up the holes. We compare four largely independent
codes for calculating LISA's parameter-estimation capabilities. All codes
are based on the Fisher-matrix approximation, but in the past they used
somewhat different signal models, source parametrizations and noise curves.
We show that once these differences are removed, the four codes give
results in extremely close agreement with each other. Using a code that
includes both spin precession and higher harmonics in the gravitational-
wave signal, we carry out Monte Carlo simulations and determine the number
of events that can be detected and accurately localized in our four
population models.
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arXiv:0811.2814v2
Semi-classical limit and minimum decoherence in the Conditional
Probability Interpretation of Quantum Mechanics
Authors: Vincent Corbin, Neil J. Cornish
(Submitted on 17 Nov 2008 (v1), last revised 2 Dec 2008 (this version, v2))
8 pages
The Conditional Probability Interpretation of Quantum Mechanics replaces
the abstract notion of time used in standard Quantum Mechanics by the
time that can be read off from a physical clock. The use of physical
clocks leads to apparent non-unitary and decoherence. Here we show that
a close approximation to standard Quantum Mechanics can be recovered from
conditional Quantum Mechanics for semi-classical clocks, and we use these
clocks to compute the minimum decoherence predicted by the Conditional
Probability Interpretation.
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arXiv:0807.2045v1
Using the etalon effect for in-situ balancing of the Advanced Virgo arm
cavities
Authors: S. Hild, A. Freise, M. Mantovani, S. Chelkowski, J. Degallaix,
R. Schilling
(Submitted on 13 Jul 2008)
12 pages, 6 Figures
Several large-scale interferometric gravitational-wave detectors use
resonant arm cavities to enhance the light power in the interferometer
arms. These cavities are based on different optical designs: One design
uses wedged input mirrors to create additional optical pick-off ports
for deriving control signals. The second design employs input mirrors
without wedge and thus offers the possibility to use the etalon effect
inside the input mirrors for tuning the finesse of the arm cavities. In
this article we introduce a concept of maximized flexibility that combines
both of these options, by featuring wedges at the input mirrors and using
the etalon effect instead in the end mirrors. We present a design for the
arm cavities of Advanced Virgo. We have used numerical simulations to
derive requirements for the manufacturing accuracy of an end mirror etalon
for Advanced Virgo. Furthermore, we give analytical approximations for
the achievable tuning range of the etalon in dependence on the reflectance,
the curvature and the orientation of the etalon back surface.
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arXiv:0811.3242v1
DC-readout of a signal-recycled gravitational wave detector
Authors: S.Hild, H.Grote, J.Degallaix, S.Chelkowski, K.Danzmann, A. Freise,
M.Hewitson, J.Hough, H.Lueck, M.Prijatelj, K.A.Strain, J.R.Smith, B.Willke
(Submitted on 19 Nov 2008)
11 pages
All first-generation large-scale gravitational wave detectors are operated
at the dark fringe and use a heterodyne readout employing radio frequency
(RF) modulation-demodulation techniques. However, the experience in the
currently running interferometers reveals several problems connected with
a heterodyne readout, of which phase noise of the RF modulation is the
most serious one. A homodyne detection scheme (DC-readout), using the
highly stabilized and filtered carrier light as local oscillator for the
readout, is considered to be a favourable alternative. Recently a DC-
readout scheme was implemented on the GEO 600 detector. We describe the
results of first measurements and give a comparison of the performance
achieved with homodyne and heterodyne readout. The implications of the
combined use of DC-readout and signal-recycling are considered.
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arXiv:0807.3041v2
A Kirchhoff-like conservation law in Regge calculus
Authors: Adrian P. Gentle, Arkady Kheyfets, Jonathan R. McDonald,
Warner A. Miller
(Submitted on 18 Jul 2008 (v1), last revised 22 Jul 2008 (this version, v2))
13 pages, 4 figures, submitted to Class. Quantum Grav
Simplicial lattices provide an elegant framework for discrete spacetimes.
The inherent orthogonality between a simplicial lattice and its
circumcentric dual yields an austere representation of spacetime which
provides a conceptually simple form of Einstein's geometric theory of
gravitation. A sufficient understanding of simplicial spacetimes has been
demonstrated in the literature for spacetimes devoid of all non-
gravitational sources. However, this understanding has not been adequately
extended to non-vacuum spacetime models. Consequently, a deep understanding
of the diffeomorphic structure of the discrete theory is lacking.
Conservation laws and symmetry properties are attractive starting points
for coupling matter with the lattice. We present a simplicial form of the
contracted Bianchi identities which is based on the E. Cartan moment of
rotation operator. These identities manifest themselves in the
conceptually-simple form of a Kirchhoff-like conservation law. This
conservation law enables one to extend Regge Calculus to non-vacuum
spacetimes, and provides a deeper understanding of the simplicial
diffeomorphism group.
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arXiv:0712.3833v2 [astro-ph]
Redshift periodicity in quasar number counts from Sloan Digital Sky Survey
Authors: John G. Hartnett
(Submitted on 22 Dec 2007 (v1), last revised 8 Feb 2008 (this version, v2))
9 pages, 3 figures
Fourier spectral analysis has been carried out on the quasar number count
as a function of redshift calculated from the quasar data of the Sloan
Digital Sky Survey DR6 data release. The results indicate that quasars
have preferred periodic redshifts with redshift intervals of 0.258, 0.312,
0.44, 0.63, and 1.1. Within their standard errors these intervals are
integer multiples 4, 5, 7, 10 and 20 of 0.062. Could this be indicative of
an intrinsic redshift for quasars as has been suggested by some?
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arXiv:0809.0334v1 [astro-ph]
Pressure gradients, shell crossing singularities and acoustic oscillations
- application to inhomogeneous cosmological models
Authors: Krzysztof Bolejko, Paul Lasky
(Submitted on 2 Sep 2008)
5 pages, 3 figures
Inhomogeneous cosmological models have recently become a very interesting
alternative to standard cosmology. This is because these models are able
to fit cosmological observations without the need for dark energy. However,
due to inhomogeneity and pressure-less matter content, these models can
suffer from shell crossing singularities. These singularities occur when
two shell of dust collide with each other leading to infinite values of
the density. In this Letter we show that if inhomogeneous pressure is
included then these singularities can be prevented from occurring over
the period of structure formation. Thus, a simple incorporation of a
gradient of pressure allows for more comprehensive studies of inhomogeneous
cosmological models and their application to cosmology.
Journal reference: MNRAS 391, L59 (2008)
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arXiv:0811.2006v1 [astro-ph]
Structure of Neutron Stars in Tensor-Vector-Scalar Theory
Authors: Paul D. Lasky, Hajime Sotani, Dimitrios Giannios
(Submitted on 12 Nov 2008)
Bekenstein's Tensor-Vector-Scalar (TeVeS) theory has had considerable
success in explaining various phenomena without the need for dark matter.
However, it is difficult to observationally discern the differences between
TeVeS and predictions made within the Lambda-cold dark matter concordance
model. This implies that alternative tests are required that independently
verify which theory is correct. For this we turn to the strong-field regime
of TeVeS. In particular, we solve the spherically symmetric equations of
hydrostatic equilibrium for a perfect fluid with a realistic equation of
state to build models of neutron stars in TeVeS. We show that causality
within the neutron star is only maintained for certain cosmological values
of the scalar field, which allows us to put constraints on this value
independently of cosmological observations. We also discuss in detail the
internal structure of neutron stars and how each of the free parameters in
the theory effects the overall size and mass of the neutron stars. In
particular, the radii of neutron stars in TeVeS can significantly differ
from those in General Relativity for certain values of the vector field
coupling, which allows us to also place extra constraints on this parameter.
Finally, we discuss future observations of neutron stars using both the
electromagnetic and gravitational wave spectrums that will allow for tests
of the appropriate theory of gravity.
Journal reference: Phys. Rev. D 78 (2008) 104019
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arXiv:0802.4118v1 [quant-ph]
A Quantum-Enhanced Prototype Gravitational-Wave Detector
Authors: Keisuke Goda, Osamu Miyakawa, Eugeniy E. Mikhailov,
Shailendhar Saraf, Rana Adhikari, Kirk McKenzie, Robert Ward,
Steve Vass, Alan J. Weinstein, Nergis Mavalvala
(Submitted on 28 Feb 2008)
7 pages, 3 figures. Accepted for publication in Nature Physics
The quantum nature of the electromagnetic field imposes a fundamental
limit on the sensitivity of optical precision measurements such as
spectroscopy, microscopy, and interferometry. The so-called quantum
limit is set by the zero-point fluctuations of the electromagnetic
field, which constrain the precision with which optical signals can
be measured. In the world of precision measurement, laser-interferometric
gravitational wave (GW) detectors are the most sensitive position meters
ever operated, capable of measuring distance changes on the order of
10^-18 m RMS over kilometer separations caused by GWs from astronomical
sources. The sensitivity of currently operational and future GW detectors
is limited by quantum optical noise. Here we demonstrate a 44% improvement
in displacement sensitivity of a prototype GW detector with suspended
quasi-free mirrors at frequencies where the sensitivity is shot-noise-
limited, by injection of a squeezed state of light. This demonstration
is a critical step toward implementation of squeezing-enhancement in
large-scale GW detectors.
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arXiv:0809.4352v1
Gravitational radiation from pulsar glitches
Authors: C. A. van Eysden, A. Melatos
(Submitted on 25 Sep 2008)
28 pages
The nonaxisymmetric Ekman flow excited inside a neutron star following a
rotational glitch is calculated analytically including stratification and
compressibility. For the largest glitches, the gravitational wave strain
produced by the hydrodynamic mass quadrupole moment approaches the
sensitivity range of advanced long-baseline interferometers. It is shown
that the viscosity, compressibility, and orientation of the star can be
inferred in principle from the width and amplitude ratios of the Fourier
peaks (at the spin frequency and its first harmonic) observed in the
gravitational wave spectrum in the plus and cross polarizations. These
transport coefficients constrain the equation of state of bulk nuclear
matter, because they depend sensitively on the degree of superfluidity.
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arXiv:0802.3422v1
Black Holes without Event Horizons
Authors: Alex B. Nielsen
(Submitted on 23 Feb 2008)
Talk at APCTP Winter School, Daejeon, Korea, 2008. 7 pages, no figures
We discuss some of the drawbacks of using event horizons to define black
holes. The reasons are both practical, physical and theoretical. We argue
that locally defined trapping horizons can remedy many of these drawbacks.
We examine of the question of whether black hole thermodynamics should be
associated with event horizons or trapping horizons. To this end we
discuss what role trapping horizons may play in black hole thermodynamics.
In addition, we show how trapping horizons may give rise to Hawking
radiation and discuss the issue of gravitational entropy.
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arXiv:0804.4435v1
Spherically symmetric trapping horizons, the Misner-Sharp mass and
black hole evaporation
Authors: Alex B. Nielsen, Dong-han Yeom
(Submitted on 28 Apr 2008)
9 pages, 10 figures
Understood in terms of pure states evolving into mixed states, the
possibility of information loss in black holes is closely related to the
global causal structure of spacetime, as is the existence of event horizons.
However, black holes need not be defined by event horizons, and in fact we
argue that in order to have a fully unitary evolution for black holes, they
should be defined in terms of something else, such as a trapping horizon.
The Misner-Sharp mass in spherical symmetry shows very simply how trapping
horizons can give rise to black hole thermodynamics, Hawking radiation and
singularities. We show how the Misner-Sharp mass can also be used to give
insights into the process of collapse and evaporation of locally defined
black holes.
-----------------------------------------------------------------------------
arXiv:0809.1711v1
Black holes without boundaries
Authors: Alex B. Nielsen
(Submitted on 10 Sep 2008)
8 pages. Invited essay for special edition of the International Journal
of Modern Physics D
We discuss some of the drawbacks of using event horizons to define black
holes and suggest ways in which black holes can be described without event
horizons, using trapping horizons. We show that these trapping horizons
give rise to thermodynamic behavior and possibly Hawking radiation too.
This raises the issue of whether the event horizon or the trapping horizon
should be seen as the true boundary of a black hole. This difference is
important if we believe that quantum gravity will resolve the central
singularity of the black hole and clarifies several of the issues
associated with black hole thermodynamics and information loss.
-----------------------------------------------------------------------------
arXiv:0801.4797v1
Geometrization of electromagnetism
Authors: Nikodem J. Poplawski
(Submitted on 30 Jan 2008)
8 pages
A general affine connection has enough degrees of freedom to describe the
classical gravitational and electromagnetic fields in the metric-affine
formulation of gravity. The gravitational field is represented by the
symmetric part of the Ricci tensor and the classical electromagnetic
field can be represented geometrically by the tensor of homothetic
curvature. The simplest metric-affine Lagrangian that depends on these
two tensors is linear in the Ricci scalar and quadratic in the tensor of
homothetic curvature, generating the Einstein-Maxwell equations. To
include spinor fields we use the metric-affine variational principle
with the tetrad and spin connection as dynamical variables. We show that
the generally covariant Dirac Lagrangian gives rise to the standard spinor
source for the Einstein-Maxwell equations, while the spinor field obeys
the nonlinear Heisenberg-Ivanenko equation with the electromagnetic
coupling.
-----------------------------------------------------------------------------
arXiv:0802.4453v1
Geometrical formulation of classical electromagnetism
Authors: Nikodem J. Poplawski
(Submitted on 29 Feb 2008)
5 pages
A general affine connection has enough degrees of freedom to describe the
classical gravitational and electromagnetic fields in the metric-affine
formulation of gravity. The gravitational field is represented in the
Lagrangian by the symmetric part of the Ricci tensor, while the classical
electromagnetic field is represented geometrically by the tensor of
homothetic curvature. We introduce matter as the four-velocity field
subject to the kinematical constraint in which the Lagrange multiplier
represents the energy density. A coupling between the four-velocity and
the trace of the nonmetricity tensor represents the electric charge
density. We show that the simplest metric-affine Lagrangian that depends
on the Ricci tensor and the tensor of homothetic curvature generates the
Einstein-Maxwell field equations, while the Bianchi identity gives the
Lorentz equation of motion. If the four-velocity couples to the torsion
vector, the Einstein equations are modified by a term that is significant
at the Planck scale and may prevent the formation of spacetime
singularities.
-----------------------------------------------------------------------------
arXiv:0803.4366v1
Variational formulation of Eisenhart's unified theory
Authors: Nikodem J. Poplawski
(Submitted on 31 Mar 2008)
9 pages
Eisenhart's unified field theory is based on a non-Riemannian affine
connection related to the covariant derivative of the electromagnetic
field tensor. The sourceless field equations of this theory arise from
vanishing of the symmetrized Ricci tensor and the torsion trace. We
formulate Eisenhart's theory from a metric-affine variational principle;
a Lagrange multiplier constraining the torsion becomes the source for
the Maxwell equations.
-----------------------------------------------------------------------------
arXiv:0806.2283v1
On variational formulation of relativistic hydrodynamics
Authors: Nikodem J. Poplawski
(Submitted on 13 Jun 2008)
4 pages
We combine Taub's and Ray's variational approaches to relativistic
hydrodynamics of perfect fluids into a simple formulation.
-----------------------------------------------------------------------------
arXiv:0712.0196v1
Robust Bayesian detection of unmodelled bursts
Authors: Antony C Searle, Patrick J Sutton, Massimo Tinto, Graham Woan
(Submitted on 2 Dec 2007)
9 pages, 1 figure, submitted to CQG Amaldi proceedings special issue
A Bayesian treatment of the problem of detecting an unmodelled
gravitational wave burst with a global network of gravitational
wave observatories reveals that several previously proposed statistics
have implicit biases that render them sub-optimal for realistic signal
populations.
Journal reference: Class.Quant.Grav.25:114038,2008
-----------------------------------------------------------------------------
arXiv:0804.1161v1
Monte-Carlo and Bayesian techniques in gravitational wave burst data
analysis
Authors: Antony C. Searle
(Submitted on 7 Apr 2008)
9 pages, submitted to GWDAW12 proceedings
Monte-Carlo simulations are used in the gravitational wave burst detection
community to demonstrate and compare the properties of different search
techniques. We note that every Monte-Carlo simulation has a corresponding
optimal search technique according to both the non-Bayesian Neyman-Pearson
criterion and the Bayesian approach, and that this optimal search technique
is the Bayesian statistic. When practical, we recommend deriving the
optimal statistic for a credible Monte-Carlo simulation, rather than
testing ad hoc statistics against that simulation.
-----------------------------------------------------------------------------
arXiv:0809.2809v1
Bayesian detection of unmodeled bursts of gravitational waves
Authors: Antony C. Searle, Patrick J. Sutton, Massimo Tinto
(Submitted on 16 Sep 2008)
14 pages, 4 figures
The data analysis problem of coherently searching for unmodeled
gravitational-wave bursts in the data generated by a global network
of gravitational-wave observatories has been at the center of research
for almost two decades. As data from these detectors is starting to be
analyzed, a renewed interest in this problem has been sparked. A Bayesian
approach to the problem of coherently searching for gravitational wave
bursts with a network of ground-based interferometers is here presented.
We demonstrate how to systematically incorporate prior information on the
burst signal and its source into the analysis. This information may range
from the very minimal, such as best-guess durations, bandwidths, or
polarization content, to complete prior knowledge of the signal waveforms
and the distribution of sources through spacetime. We show that this
comprehensive Bayesian formulation contains several previously proposed
detection statistics as special (unphysical) limiting cases, and
demonstrate that it outperforms them.
-----------------------------------------------------------------------------
arXiv:0712.0427v1
Analogue spacetimes: Toy models for "quantum gravity''
Authors: Matt Visser (Victoria University of Wellington),
Silke Weinfurtner (Victoria University of Wellington)
(Submitted on 4 Dec 2007)
24 pages; Based on a talk at the conference: From Quantum to Emergent
Gravity: Theory and Phenomenology, June 11-15 2007, Trieste, Italy
Why are "analogue spacetimes'' interesting? For the purposes of this
workshop the answer is simple: Analogue spacetimes provide one with
physically well-defined and physically well-understood concrete models
of many of the phenomena that seem to be part of the yet incomplete
theory of "quantum gravity'', or more accessibly, "quantum gravity
phenomenology''. Indeed "analogue spacetimes'' provide one with concrete
models of "emergence'' (whereby the effective low-energy theory can be
radically different from the high-energy microphysics). They also provide
many concrete and controlled models of "Lorentz symmetry breaking'', and
extensions of the usual notions of pseudo-Riemannian geometry such as
"rainbow spacetimes'', and pseudo-Finsler geometries, and more. I will
provide an overview of the key items of "unusual physics'' that arise in
analogue spacetimes, and argue that they provide us with hints of what
we should be looking for in any putative theory of "quantum gravity''.
For example: The dispersion relations that naturally arise in the known
emergent/analogue spacetimes typically violate analogue Lorentz
invariance at high energy, but do not do so in completely arbitrary
manner. This suggests that a search for arbitrary violations of Lorentz
invariance is possibly overkill: There are a number of natural and
physically well-motivated restrictions one can put on emergent/ analogue
dispersion relations, considerably reducing the plausible parameter space.
Journal reference: PoSQG-Ph:042,2007
-----------------------------------------------------------------------------
arXiv:0712.1619v1
Cosmodynamics: Energy conditions, Hubble bounds, density bounds, time and
distance bounds
Authors: Celine Cattoen (Victoria University of Wellington),
Matt Visser (Victoria University of Wellington)
(Submitted on 10 Dec 2007)
21 pages, 2 figures
We refine and extend a programme initiated by one of the current authors
[Science 276 (1997) 88; Phys. Rev. D56 (1997) 7578] advocating the use
of the classical energy conditions of general relativity in a cosmological
setting to place very general bounds on various cosmological parameters.
We show how the energy conditions can be used to bound the Hubble parameter
H(z), Omega parameter Omega(z), density rho(z), distance d(z), and lookback
time T(z) as (relatively) simple functions of the redshift z, present-epoch
Hubble parameter H_0, and present-epoch Omega parameter Omega_0. We compare
these results with related observations in the literature, and confront the
bounds with the recent supernova data.
Journal reference: Class.Quant.Grav.25:165013,2008
-----------------------------------------------------------------------------
arXiv:0801.2673v1
Cosmological particle production in emergent rainbow spacetimes
Authors: Silke Weinfurtner, Piyush Jain, Matt Visser, C.W. Gardiner
(Submitted on 17 Jan 2008)
We investigate cosmological particle production in spacetimes where Lorentz
invariance emerges in the infrared limit, but is explicitly broken in the
ultraviolet regime. Our specific model focuses on the boost subgroup that
supports CPT invariance and results in a momentum-dependent dispersion
relation. Motivated by previous studies on spacetimes emerging from a
microscopic substrate, we show how these modifications naturally lead to
momentum-dependent rainbow metrics. Firstly, we investigate the possibility
of reproducing cosmological particle production in spacetimes emerging from
real Bose gases. We have studied the influence of non-perturbative
ultraviolet corrections in time-dependent analogue spacetimes, leading to
momentum-dependent emergent rainbow spacetimes. Within certain limits the
analogy is sufficiently good to simulate relativistic quantum field theory
in time-dependent classical backgrounds, and the quantum effects are
approximately robust against the model-dependent modifications. Secondly,
we analyze how significantly the particle production process deviates from
the common picture. While very low-energy modes do not see the difference
at all, some modes "re-enter the Hubble horizon" during the inflationary
epoch, and extreme ultraviolet modes are completely insensitive to the
expansion.
-----------------------------------------------------------------------------
arXiv:0804.1346v1
On the phenomenon of emergent spacetimes: An instruction guide for
experimental cosmology
Authors: Silke Weinfurtner (University of British Columbia),
Matt Visser (Victoria University of Wellington),
Piyush Jain (University of Otago), C.W. Gardiner (University of Otago)
(Submitted on 8 Apr 2008)
19 pages; Based on a talk at the conference: From Quantum to Emergent
Gravity: Theory and Phenomenology, June 11-15 2007, Trieste, Italy
We present a toy model where spacetime is emergent from a more fundamental
microscopic system, and investigate the gray area interpolating between
the collective and free-particle regimes. For a period of rapid exponential
growth in the analogue universe, we argue that the intermediate regime is
best described by a coloured potpourri of geometries -- a "rainbow
geometry". This can be viewed as an alternative approach towards
understanding quantum field theories in the presence of Lorentz-symmetry
breaking at ultraviolet scales. Firstly, it is pointed out that
cosmological particle production in our emergent FRW-type analogue
universe, when compared to conventional semi-classical quantum gravity,
is only temporarily robust against model-specific deviations from Lorentz
invariance. Secondly, it is possible to carry out a straightforward
quantitative analysis to estimate a suitable parameter regime for
experimental (analogue) cosmology.
Journal reference: PoSQG-Ph:044,2007
-----------------------------------------------------------------------------
arXiv:0806.0950v1
The pseudo-Finslerian spacetimes of birefringent optics
Authors: Jozef Skakala (Victoria University of Wellington),
Matt Visser (Victoria University of Wellington)
(Submitted on 5 Jun 2008)
19 pages
It is reasonably well-known that birefringent crystal optics can to some
extent be described by the use of pseudo-Finslerian spacetimes (an
extension of pseudo-Riemannian spacetime). What is less commonly
appreciated is that there are two separate and quite disjoint pseudo-
Finsler structures for the two photon polarizations, and further, that
there are separate tangent-space pseudo-Finsler structures defined by
the group velocity and co-tangent-space pseudo-co-Finsler structures
defined by the phase velocity. The inter-connections between these four
separate pseudo-Finsler structures are rather subtle. One particular
source of technical difficulty is the fact that because physicists need
to use pseudo-Finsler structures to describe propagation of signals,
there will be nonzero null vectors in both the tangent and cotangent
spaces -- this causes significant problems in that many of the
mathematical results normally obtained for "usual'' (Euclidean signature)
Finsler structures either do not apply, or require significant
modifications to their formulation.
We shall first provide a few basic definitions, and then present a
tutorial outline of the relevant physics of birefringent optics,
explicitly demonstrating the interpretation in terms of pseudo-Finsler
spacetimes. We shall then discuss the tricky issues that arise when
trying to inter-relate the various pseudo-Finsler structures we
encounter, and finish by connecting these technical questions (which
of course arise in what is a physically a very well-understood situation)
back to ongoing research into possible extensions and modifications of
general relativity.
-----------------------------------------------------------------------------
arXiv:0806.2186v1
Bounding the Hubble flow in terms of the w parameter
Authors: Celine Cattoen (Victoria University of Wellington),
Matt Visser (Victoria University of Wellington)
(Submitted on 13 Jun 2008)
15 pages
The last decade has seen increasing efforts to circumscribe and bound
the cosmological Hubble flow in terms of model-independent constraints
on the cosmological fluid - such as, for instance, the classical energy
conditions of general relativity. Quite a bit can certainly be said in
this regard, but much more refined bounds can be obtained by placing
more precise constraints (either theoretical or observational) on the
cosmological fluid. In particular, the use of the w-parameter (w=p/rho)
has become increasingly common as a surrogate for trying to say something
about the cosmological equation of state. Herein we explore the extent
to which a constraint on the w-parameter leads to useful and nontrivial
constraints on the Hubble flow, in terms of constraints on density rho(z),
Hubble parameter H(z), density parameter Omega(z), cosmological distances
d(z), and lookback time T(z). In contrast to other partial results in the
literature, we carry out the computations for arbitrary values of the
space curvature k in [-1,0,+1], equivalently for arbitrary Omega_0 <= 1.
Journal reference: JCAP11(2008)024
-----------------------------------------------------------------------------
arXiv:0806.2209v2
Bounding the greybody factors for Schwarzschild black holes
Authors: Petarpa Boonserm (Victoria University of Wellington),
Matt Visser (Victoria University of Wellington)
(Submitted on 13 Jun 2008 (v1), last revised 23 Jun 2008 (this version, v2))
5 pages
Greybody factors in black hole physics modify the naive Planckian spectrum
that is predicted for Hawking radiation when working in the limit of
geometrical optics. We consider the Schwarzschild geometry in (3+1)
dimensions, and analyze the Regge-Wheeler equation for arbitrary particle
spin S and wave-mode angular momentum L, deriving rigourous bounds on the
greybody factors as a function of S, L, wave frequency (omega), and the
black hole mass, m.
Journal reference: Phys.Rev.D78:101502,2008
-----------------------------------------------------------------------------
arXiv:0808.1931v1
Quantum Interest in (3+1) dimensional Minkowski space
Authors: Gabriel Abreu (Victoria University of Wellington),
Matt Visser (Victoria University of Wellington)
(Submitted on 14 Aug 2008)
8 pages
The so-called "Quantum Inequalities", and the "Quantum Interest Conjecture",
use quantum field theory to impose significant restrictions on the temporal
distribution of the energy density measured by a time-like observer,
potentially preventing the existence of exotic phenomena such as
"Alcubierre warp-drives" or "traversable wormholes". Both the quantum
inequalities and the quantum interest conjecture can be reduced to
statements concerning the existence or non-existence of bound states for
a certain one-dimensional quantum mechanical pseudo-Hamiltonian. Using this
approach, we shall provide a simple proof of one version of the Quantum
Interest Conjecture in (3+1) dimensional Minkowski space.
-----------------------------------------------------------------------------
arXiv:0808.2068v1
Explicit form of the Mann-Marolf surface term in (3+1) dimensions
Authors: Matt Visser (Victoria University of Wellington)
(Submitted on 14 Aug 2008)
4 pages
The Mann-Marolf surface term is a specific candidate for the "reference
background term" that is to be subtracted from the Gibbons-Hawking
surface term in order make the total gravitational action of
asymptotically flat spacetimes finite. That is, the total gravitational
action is taken to be: (Einstein-Hilbert bulk term) + (Gibbons-Hawking
surface term) - (Mann-Marolf surface term).
As presented by Mann and Marolf, their surface term is specified
implicitly in terms of the Ricci tensor of the boundary. Herein I
demonstrate that for the physically interesting case of a (3+1)
dimensional bulk spacetime, the Mann-Marolf surface term can be
specified explicitly in terms of the Einstein tensor of the (2+1)
dimensional boundary.
-----------------------------------------------------------------------------
arXiv:0809.0537v1
Cosmographic Hubble fits to the supernova data
Authors: Celine Cattoen (Victoria University of Wellington),
Matt Visser (Victoria University of Wellington)
(Submitted on 3 Sep 2008)
28 pages
The Hubble relation between distance and redshift is a purely cosmographic
relation that depends only on the symmetries of a FLRW spacetime, but does
not intrinsically make any dynamical assumptions. This suggests that it
should be possible to estimate the parameters defining the Hubble relation
without making any dynamical assumptions. To test this idea, we perform a
number of inter-related cosmographic fits to the legacy05 and gold06
supernova datasets. Based on this supernova data, the "preponderance of
evidence" certainly suggests an accelerating universe. However we would
argue that (unless one uses additional dynamical and observational
information) this conclusion is not currently supported "beyond reasonable
doubt". As part of the analysis we develop two particularly transparent
graphical representations of the redshift-distance relation -
representations in which acceleration versus deceleration reduces to the
question of whether the relevant graph slopes up or down. Turning to the
details of the cosmographic fits, three issues in particular concern us:
First, the fitted value for the deceleration parameter changes
significantly depending on whether one performs a chi^2 fit to the
luminosity distance, proper motion distance or other suitable distance
surrogate. Second, the fitted value for the deceleration parameter changes
significantly depending on whether one uses the traditional redshift
variable z, or what we shall argue is on theoretical grounds an improved
parameterization y=z/(1+z). Third, the published estimates for systematic
uncertainties are sufficiently large that they certainly impact on, and
to a large extent undermine, the usual purely statistical tests of
significance. We conclude that the supernova data should be treated with
some caution.
Journal reference: Phys.Rev.D78:063501,2008
-----------------------------------------------------------------------------
arXiv:0809.0907v1
Traversable wormholes: Some simple examples
Authors: Matt Visser (Victoria University of Wellington)
(Submitted on 4 Sep 2008)
Pre-arXiv article from 1989; 7 pages, no figures.
Building on the work of Morris, Thorne, and Yurtsever, some particularly
simple examples of traversable wormholes are exhibited. These examples
are notable both because the analysis is not limited to spherically
symmetric cases, and because it is possible to in some sense minimize
the use of exotic matter. In particular, it is possible for a traveller
to traverse such a wormhole without passing through a region of exotic
matter. As in previous analyses, the weak energy condition is violated
in these traversable wormholes.
Journal reference: Phys.Rev.D39:3182-3184,1989
-----------------------------------------------------------------------------
arXiv:0809.0927v1
Traversable wormholes from surgically modified Schwarzschild spacetimes
Authors: Matt Visser (Victoria University of Wellington)
(Submitted on 4 Sep 2008)
Pre-arXiv article from 1989; 12 pages, no figures.
In this paper I present a new class of traversable wormholes. This is
done by surgically grafting two Schwarzschild spacetimes together in
such a way that no event horizon is permitted to form. This surgery
concentrates a non--zero stress--energy on the boundary layer between
the two asymptotically flat regions. I shall investigate this stress-
energy in detail using the "junction condition" formalism. A feature
of the present analysis is that this class of traversable wormholes is
sufficiently simple for a (partial) dynamical stability analysis to be
carried out. The stability analysis places constraints on the equation
of state of the exotic matter that comprises the throat of the wormhole.
Journal reference: Nucl.Phys.B328:203-212,1989
-----------------------------------------------------------------------------
arXiv:0810.4376v1
Birefringence in pseudo-Finsler spacetimes
Authors: Jozef Skakala (Victoria University of Wellington),
Matt Visser (Victoria University of Wellington)
(Submitted on 24 Oct 2008)
8 pages; Talk delivered by Jozef Skakala at the NEB XIII conference,
(Recent Developments in Gravity), Thessalonika, Greece, June 2008
Based on the analogue spacetime programme, and many other ideas currently
mooted in "quantum gravity", there is considerable ongoing speculation
thatthe usual pseudo-Riemannian (Lorentzian) manifolds of general
relativity might eventually be modified at short distances. Two specific
modifications that are often advocated are the adoption of Finsler
geometries (or more specifically, pseudo-Finsler spacetimes) and the
possibility of birefringence (or more generally, multi-refringence). We
have investigated the possibility of whether it is possible to usefully
and cleanly deal with these two possibilities simultaneously. That is,
given two (or more) "signal cones": Is it possible to naturally and
intuitively construct a "unified" pseudo-Finsler spacetime such that the
pseudo-Finsler metric is null on these "signal cones", but has no other
zeros or singularities? Our results are much less encouraging than we had
originally hoped, and suggest that while pseudo-Finsler spacetimes are
certainly useful constructs, it is physically more appropriate to think
of physics as taking place in a single topological manifold that carries
several distinct pseudo-Finsler metrics, one for each polarization mode.
-----------------------------------------------------------------------------
arXiv:0807.1710v2
Dynamical Analysis of the Structure of Neutron Star Critical Collapses
Authors: M.-B. Wan, K.-J. Jin, W.-M. Suen
(Submitted on 10 Jul 2008 (v1), last revised 10 Jul 2008 (this version, v2))
Poster version presented at the "2nd Course of the International School on
Astrophysical Relativity", Erice, Italy, June 27th - July 5th
in et al reported that axisymmetric simulations of NS-like objects with
polytropic EOS undergo critical gravitational collapse. As the critical
collapse observed via fine-tuning of the adiabatic index $\Gamma$, they
conjecture that critical phenomena may occur in realistic astrophysical
scenarios. To clarify the implications this numerical observation has on
realistic astrophysical scenarios, here, we perform dynamical analysis on
the structure of the critical collapse observed in the former work. We
report the time scales and oscillation frequencies exhibited by the
critical solution and compare these results with values obtained from
analytic perturbative mode analysis of equilibrium TOV configurations.
We also establish the universality of the critical solution with respect
to a 1-parameter family of initial data as well as the phase space
manifold of the critical collapse.
-----------------------------------------------------------------------------
arXiv:0810.2631v1
The fluid/gravity correspondence: Lectures notes from the 2008 Summer
School on Particles, Fields, and Strings
Authors: Nicola Ambrosetti, James Charbonneau, Silke Weinfurtner
(Submitted on 15 Oct 2008)
21 pages, 5 figures
This is a paper compiled by students of the 2008 Summer School on
Particles, Fields, and Strings held at the University of British
Columbia on lectures given by Veronika Hubeny as understood and
interpreted by the authors. We start with an introduction to the
AdS/CFT duality. More specifically, we discuss the correspondence
between relativistic, conformal hydrodynamics and Einstein's theory
of gravity. Within our framework the Einstein equations are an effective
description for the string theory in the bulk of AdS_5 spacetime and the
hydrodynamic fluid equations represent the conformal field theory near
thermal equilibrium on the boundary. In particular we present a new
technique for calculating properties in fluid dynamics using the stress-
energy tensor induced on the boundary, by the gravitational field in the
bulk, and comparing it with the form of the stress-energy tensor from
hydrodynamics. A detailed treatment can be found in [JHEP 02 (2008) 045]
and [arXiv:0803.2526].
-----------------------------------------------------------------------------
arXiv:0712.3982v1
Gravitational energy and cosmic acceleration
Authors: David L. Wiltshire
(Submitted on 24 Dec 2007)
9 pages, 2 figures. An essay which received Honorable Mention in the 2007
GRF Essay Competition.
Cosmic acceleration is explained quantitatively, as an apparent effect
due to gravitational energy differences that arise in the decoupling of
bound systems from the global expansion of the universe. "Dark energy"
is a misidentification of those aspects of gravitational energy which by
virtue of the equivalence principle cannot be localised, namely gradients
in the energy due to the expansion of space and spatial curvature
variations in an inhomogeneous universe. A new scheme for cosmological
averaging is proposed which solves the Sandage-de Vaucouleurs paradox.
Concordance parameters fit supernovae luminosity distances, the angular
scale of the sound horizon in the CMB anisotropies, and the effective
comoving baryon acoustic oscillation scale seen in galaxy clustering
statistics. Key observational anomalies are potentially resolved, and
unique predictions made, including a quantifiable variance in the Hubble
flow below the scale of apparent homogeneity.
Journal reference: Int.J.Mod.Phys.D17:641-649,2008
-----------------------------------------------------------------------------
arXiv:0712.3984v1 [astro-ph]
Dark energy without dark energy
Authors: David L. Wiltshire
(Submitted on 24 Dec 2007)
32 pages, 8 figures
An overview is presented of a recently proposed "radically conservative"
solution to the problem of dark energy in cosmology. The proposal yields
a model universe which appears to be quantitatively viable, in terms of
its fit to supernovae luminosity distances, the angular scale of the
sound horizon in the cosmic microwave background (CMB) anisotropy
spectrum, and the baryon acoustic oscillation scale. It may simultaneously
resolve key anomalies relating to primordial lithium abundances, CMB
ellipticity, the expansion age of the universe and the Hubble bubble
feature. The model uses only general relativity, and matter obeying the
strong energy condition, but revisits operational issues in interpreting
average measurements in our presently inhomogeneous universe, from first
principles. The present overview examines both the foundational issues
concerning the definition of gravitational energy in a dynamically
expanding space, the quantitative predictions of the new model and its
best-fit cosmological parameters, and the prospects for an era of new
observational tests in cosmology.
Journal reference: In "Dark Matter in Astroparticle and Particle Physics:
Proceedings of the 6th International Heidelberg Conference", eds H.V.
Klapdor-Kleingrothaus and G.F. Lewis, (World Scientific, Singapore, 2008)
pp 565-596
-----------------------------------------------------------------------------
arXiv:0809.1183v3
Cosmological equivalence principle and the weak-field limit
Authors: David L. Wiltshire
(Submitted on 8 Sep 2008 (v1), last revised 24 Oct 2008 (this version, v3))
17 pages, 5 figures
he strong equivalence principle is extended in application to averaged
dynamical fields in cosmology to include the role of the average density
in the determination of inertial frames. The resulting cosmological
equivalence principle is applied to the problem of synchronisation of
clocks in the observed universe. Once density perturbations grow to give
density contrasts of order one on scales of tens of megaparsecs, the
integrated deceleration of the local background regions of voids relative
to galaxies must be accounted for in the relative synchronisation of clocks
of ideal observers who measure an isotropic cosmic microwave background.
The relative deceleration of the background can be expected to represent a
scale in which weak-field Newtonian dynamics should be modified to account
for dynamical gradients in the Ricci scalar curvature of space. This
acceleration scale is estimated using the best-fit nonlinear bubble model
of the universe with backreaction. At redshifts z < 0.25 the scale is
found to coincide with the empirical acceleration scale of modified
Newtonian dynamics. At larger redshifts the scale varies in a manner which
is likely to be important for understanding dynamics of galaxy clusters,
and structure formation. Although the relative deceleration, typically of
order 10^{-10} m/s^2, is small, when integrated over the lifetime of the
universe it amounts to an accumulated relative difference of 38% in the
rate of average clocks in galaxies as compared to volume-average clocks
in the emptiness of voids. A number of foundational aspects of the
cosmological equivalence principle are also discussed, including its
relation to Mach's principle, the Weyl curvature hypothesis and the
initial conditions of the universe.
Journal reference: Phys.Rev.D78:084032,2008
******************************************************************************
ABSTRACTS FROM THE LIGO SCIENTIFIC COLLABORATION at gr-qc,
December 2006 - November 2007
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.
-----------------------------------------------------------------------------
arXiv:0712.2050v3
Search of S3 LIGO data for gravitational wave signals from spinning black
hole and neutron star binary inspirals
Authors: The LIGO Scientific Collaboration: B. Abbott, et al
(Submitted on 12 Dec 2007 (v1), last revised 30 Jun 2008 (this version, v3))
18 pages, 8 figures
We report on the methods and results of the first dedicated search for
gravitational waves emitted during the inspiral of compact binaries with
spinning component bodies. We analyze 788 hours of data collected during
the third science run (S3) of the LIGO detectors. We searched for binary
systems using a detection template family designed specially to capture
the effects of the spin-induced precession of the orbital plane. We present
details of the techniques developed to enable this search for spin-modulated
gravitational waves, highlighting the differences between this and other
recent searches for binaries with non-spinning components. The template bank
we employed was found to yield high matches with our spin-modulated target
waveform for binaries with masses in the asymmetric range 1.0 Msol < m1 <
3.0 Msol and 12.0 Msol < m2 < 20.0 Msol which is where we would expect the
spin of the binary's components to have significant effect. We find that our
search of S3 LIGO data had good sensitivity to binaries in the Milky Way and
to a small fraction of binaries in M31 and M33 with masses in the range 1.0
Msol < m1, m2 < 20.0Msol. No gravitational wave signals were identified
during this search. Assuming a binary population with spinning components
and Gaussian distribution of masses representing a prototypical neutron
star - black hole system with m1 ~ 1.35 Msol and m2 ~ 5 Msol, we calculate
the 90%-confidence upper limit on the rate of coalescence of these systems
to be 15.9 yr^-1 L_10^-1, where L_10 is 10^10 times the blue light
luminosity of the Sun.
Journal reference: Phys.Rev.D78:042002,2008
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arXiv:0801.3429v1
Searching for stochastic gravitational-wave background with the
co-located LIGO interferometers
Authors: Nickolas V Fotopoulos, for the LIGO Scientific Collaboration
(Submitted on 22 Jan 2008)
Proceedings paper from the 7th Edoardo Amaldi Conference on Gravitational
Waves, held in Sydney, Australia from 8-14 July 2007.
This paper presents techniques developed by the LIGO Scientific
Collaboration to search for the stochastic gravitational-wave
background using the co-located pair of LIGO interferometers at Hanford,
WA. We use correlations between interferometers and environment monitoring
instruments, as well as time-shifts between two interferometers (described
here for the first time) to identify correlated noise from non-
gravitational sources. We veto particularly noisy frequency bands and
assess the level of residual non-gravitational coupling that exists in
the surviving data.
Journal reference: J.Phys.Conf.Ser.122:012032,2008
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arXiv:0802.0393v1
GRB-triggered searches for gravitational waves in LIGO data
Authors: Alexander Dietz, for the LIGO Scientific Collaboration
(Submitted on 4 Feb 2008)
5 pages, 3 figures, contributed talk, submitted to the proceedings of
Gamma Ray Bursts 2007, Santa Fe, New Mexico, November 5-9 2007
The LIGO gravitational wave detectors have recently reached their design
sensitivity and finished a two-year science run. During this period one
year of data with unprecedented sensitivity has been collected. I will
briefly describe the status of the LIGO detectors and the overall quality
of the most recent science run. I also will present results of a search
for inspiral waveforms in gravitational wave data coincident with the
short gamma ray burst detected on 1st February 2007, with its sky
location error box overlapping a spiral arms of M31. No gravitational
wave signals were detected and a binary merger in M31 can be excluded at
the 99% confidence level.
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arXiv:0802.4320v1
Astrophysically Triggered Searches for Gravitational Waves: Status and
Prospects
Authors: The LIGO Scientific Collaboration, Virgo Collaboration
(Submitted on 29 Feb 2008)
In gravitational-wave detection, special emphasis is put onto searches
that focus on cosmic events detected by other types of astrophysical
observatories. The astrophysical triggers, e.g. from gamma-ray and
X-ray satellites, optical telescopes and neutrino observatories, provide
a trigger time for analyzing gravitational wave data coincident with the
event. In certain cases the expected frequency range, source energetics,
directional and progenitor information is also available. Beyond allowing
the recognition of gravitational waveforms with amplitudes closer to the
noise floor of the detector, these triggered searches should also lead to
rich science results even before the onset of Advanced LIGO. In this paper
we provide a broad review of LIGO's astrophysically triggered searches
and the sources they target.
Journal reference: Class.Quant.Grav.25:114051,2008
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arXiv:0804.1747v1
The Einstein@Home search for periodic gravitational waves in LIGO S4 data
Authors: LIGO Scientific Collaboration: B. Abbott, et al
(Submitted on 10 Apr 2008)
29 pages, 19 figures
A search for periodic gravitational waves, from sources such as isolated
rapidly-spinning neutron stars, was carried out using 510 hours of data
from the fourth LIGO science run (S4). The search was for quasi-
monochromatic waves in the frequency range from 50 Hz to 1500 Hz, with
a linear frequency drift f-dot (measured at the solar system barycenter)
in the range -f/tau < f-dot < 0.1 f/tau, where the minimum spin-down age
tau was 1000 years for signals below 300 Hz and 10000 years above 300 Hz.
The main computational work of the search was distributed over
approximately 100000 computers volunteered by the general public. This
large computing power allowed the use of a relatively long coherent
integration time of 30 hours, despite the large parameter space searched.
No statistically significant signals were found. The sensitivity of the
search is estimated, along with the fraction of parameter space that was
vetoed because of contamination by instrumental artifacts. In the 100 Hz
to 200 Hz band, more than 90% of sources with dimensionless gravitational
wave strain amplitude greater than 1e-23 would have been detected.
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arXiv:0805.2412v2
Detection Confidence Tests for Burst and Inspiral Candidate Events
Authors: R. Gouaty, for the LIGO Scientific Collaboration
(Submitted on 15 May 2008 (v1), last revised 17 Sep 2008 (this version, v2))
15 pages, 8 figures, Contribution to 12th Gravitational Wave Data Analysis
Workshop.
The LIGO Scientific Collaboration (LSC) is developing and running analysis
pipelines to search for gravitational-wave transients emitted by
astrophysical events such as compact binary mergers or core-collapse
supernovae. However, because of the non-Gaussian, non-stationary nature of
the noise exhibited by the LIGO detectors, residual false alarms might be
found at the end of the pipelines. A critical aspect of the search is then
to assess our confidence for gravitational waves and to distinguish them
from those false alarms. Both the 'Compact Binary Coalescence' and the
'Burst' working groups have been developing a detection checklist for the
validation of candidate-events, consisting of a series of tests which aim
to corroborate a detection or to eliminate a false alarm. These tests
include for example data quality checks, analysis of the candidate
appearance, parameter consistency studies and coherent analysis. In this
paper, the general methodology used for candidate validation is presented.
The method is illustrated with an example of simulated gravitational-wave
signal and a false alarm.
Journal reference: Class.Quant.Grav.25:184006,2008
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arXiv:0805.4758v2 [astro-ph]
Beating the spin-down limit on gravitational wave emission from the Crab
pulsar
Authors: The LIGO Scientific Collaboration: B. Abbott, et al
(Submitted on 30 May 2008 (v1), last revised 22 Jul 2008 (this version, v2))
Accepted for Ap. J. Lett. Minor changes in results due to calibration
correction
We present direct upper limits on gravitational wave emission from the
Crab pulsar using data from the first nine months of the fifth science
run of the Laser Interferometer Gravitational-wave Observatory (LIGO).
These limits are based on two searches. In the first we assume that the
gravitational wave emission follows the observed radio timing, giving an
upper limit on gravitational wave emission that beats indirect limits
inferred from the spin-down and braking index of the pulsar and the
energetics of the nebula. In the second we allow for a small mismatch
between the gravitational and radio signal frequencies and interpret our
results in the context of two possible gravitational wave emission
mechanisms.
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arXiv:0807.2834v2
First joint search for gravitational-wave bursts in LIGO and GEO600 data
Authors: LIGO Scientific Collaboration: B. Abbott, et al
(Submitted on 17 Jul 2008 (v1), last revised 15 Oct 2008 (this version, v2))
30 pages, 8 figures
We present the results of the first joint search for gravitational-wave
bursts by the LIGO and GEO600 detectors. We search for bursts with
characteristic central frequencies in the band 768 to 2048 Hz in the
data acquired between the 22nd of February and the 23rd of March, 2005
(fourth LSC Science Run - S4). We discuss the inclusion of the GEO600 data
in the Waveburst-CorrPower pipeline that first searches for coincident
excess power events without taking into account differences in the antenna
responses or strain sensitivities of the various detectors. We compare the
performance of this pipeline to that of the coherent Waveburst pipeline
based on the maximum likelihood statistic. This likelihood statistic is
derived from a coherent sum of the detector data streams that takes into
account the antenna patterns and sensitivities of the different detectors
in the network. We find that the coherentWaveburst pipeline is sensitive
to signals of amplitude 30 - 50% smaller than the Waveburst-CorrPower
pipeline. We perform a search for gravitational-wave bursts using both
pipelines and find no detection candidates in the S4 data set when all
four instruments were operating stably.
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arXiv:0810.0283v1
All-sky LIGO Search for Periodic Gravitational Waves in the Early S5 Data
Authors: LIGO Scientific Collaboration
(Submitted on 1 Oct 2008)
6 pages, 1 figure
We report on an all-sky search with the LIGO detectors for periodic
gravitational waves in the frequency range 50--1100 Hz and with the
frequency's time derivative in the range -5.0E-9 Hz/s to zero. Data
from the first eight months of the fifth LIGO science run (S5) have
been used in this search, which is based on a semi-coherent method
(PowerFlux) of summing strain power. Observing no evidence of periodic
gravitational radiation, we report 95% confidence-level upper limits
on radiation emitted by any unknown isolated rotating neutron stars
within the search range. Strain limits below 1.E-24 are obtained over
a 200-Hz band, and the sensitivity improvement over previous searches
increases the spatial volume sampled by an average factor of about 100
over the entire search band. For a neutron star with nominal equatorial
ellipticity of 1.0E-6, the search is sensitive to distances as great as
500 pc - a range that could encompass many undiscovered neutron stars,
albeit only a tiny fraction of which would likely be rotating fast enough
to be accessible to LIGO. This ellipticity is at the upper range thought
to be sustainable by conventional neutron stars and well below the
maximum sustainable by a strange quark star.
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