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