General Relativity and Gravitation

PREFACE.

ORGANISING COMMITTEES.

SPONSORS.

OPENING ADDRESS.

JOHN LIGHTON SYNGE: A MEMORIAL LECTURE.

COMMENTS ON THE DEATH OF PETER BERGMANN.

CONTENTS.

Numerical relativity has come a long way in the last three decades and is now reaching a state of maturity. We are gaining a deeper understanding of the fundamental theoretical issues related to the field, from the well posedness of the Cauchy problem, to better gauge conditions, improved boundary treatment, and more realistic initial data. There has also been important work both in numerical methods and software engineering. All these developments have come together to allow the construction of several advanced fully three-dimensional codes capable of dealing with both matter and black holes. In this manuscript I make a brief review of the current status of the field.

No abstract received.

The status, progress and plans for the Interferometer Gravitational Wave Detectors are presented. Resonant Bar and Interferometric detectors are complementary approaches to gravitational wave detection. Resonant Bars are generally narrow band cryogenic detectors sensitive at frequencies of about 1 KHz. Interferometers are long baseline broad-band detectors covering a frequencies range of about 10 to 10⁴ Hz, having sensitivity to lower frequency gravitational radiation. In this presentation I review the techniques and status of both the resonant bar detectors and gravitational wave interferometers worldwide.

No abstract received.

We review selected recent results concerning the global structure of solutions of the vacuum Einstein equations. The topics covered include quasi-local mass, strong cosmic censorship, non-linear stability, new constructions of solutions of the constraint equations, improved understanding of asymptotic properties of the solutions, existence of solutions with low regularity, and construction of initial data with trapped surfaces or apparent horizons.

The Euclidean path integral over all topologically trivial metrics can be done by time slicing and so is unitary when analytically continued to the Lorentzian. On the other hand, the path integral over all topologically non-trivial metrics is asymptotically independent of the initial state. Thus the total path integral is unitary and information is not lost in the formation and evaporation of black holes. The way the information gets out seems to be that a true event horizon never forms, just an apparent horizon.

In brane-worlds, our universe is assumed to be a submanifold, or brane, embedded in a higher-dimensional bulk spacetime. Focusing on scenarios with a curved five-dimensional bulk spacetime, I discuss their gravitational and cosmological properties.

We review recent progress in understanding certain aspects of the thermodynamics of black holes and other horizons. Our discussion centers on various “entropy bounds” which have been proposed in the literature and on the current understanding of how such bounds are not required for the semi-classical consistency of black hole thermodynamics. Instead, consistency under certain extreme circumstances is provided by two effects. The first is simply the exponential enhancement of the rate at which a macrostate with large entropy is emitted in any thermal process. The second is a new sense in which the entropy of an “object” depends on the observer making the measurement, so that observers crossing the horizon measure a different entropy flux across the horizon than do observers remaining outside. In addition to the review, some recent criticisms are addressed. In particular, additional arguments and detailed numerical calculations showing the observer dependence of entropy are presented in a simple model. This observer-dependence may have further interesting implications for the thermodynamics of black holes.

No abstract received.

The cosmological tests are tight enough now to show that the Friedmann-Lemaître Λ–CDM cosmological model almost certainly is a useful approximation. This means general relativity theory passes significant tests of the extrapolation of some fifteen orders of magnitude from the length scales of the precision tests of gravity physics.

No abstract received.

The self-force describes the effect of a particle’s own gravitational field on its motion. While the motion is geodesic in the test-mass limit, it is accelerated to first order in the particle’s mass. In this contribution I review the foundations of the self-force, and show how the motion of a small black hole can be determined by matched asymptotic expansions of a perturbed metric. I next consider the case of a point mass, and show that while the retarded field is singular on the world line, it can be unambiguously decomposed into a singular piece that exerts no force, and a smooth remainder that is responsible for the acceleration. I also describe the recent efforts, by a number of workers, to compute the self-force in the case of a small body moving in the field of a much more massive black hole. The motivation for this work is provided in part by the Laser Interferometer Space Antenna, which will be sensitive to low-frequency gravitational waves. Among the sources for this detector is the motion of small compact objects around massive (galactic) black holes. To calculate the waves emitted by such systems requires a detailed understanding of the motion, beyond the test-mass approximation.

It is possible that superstrings, as well as other one-dimensional branes, could have been produced in the early universe and then expanded to cosmic size today. I discuss the conditions under which this will occur, and the signatures of these strings. Such cosmic superstrings could be the brightest objects visible in gravitational wave astronomy, and might be distinguishable from gauge theory cosmic strings by their network properties.

No abstract received.

By the early 1970s the astrophysically-relevant theoretical properties of black holes - the Kerr metric, the 'no hair' theorems, and so forth - were well established. But it took much longer for the observers to discover well-authenticated candidates. By now, the evidence points insistently towards the existence of dark objects, with deep potential wells and 'horizons' through which matter can pass into invisibility. However, observers cannot yet definitively confirm the form of the metric in the strong-gravity region, though there is exciting progress towards this goal.

No abstract received.

No abstract received.

No abstract received.

Even in these days of remarkable advances on the experimental side of gravitational physics, general relativity remains very much a mathematical science. Not surprisingly, the use of serious mathematical ideas and tools permeated many of the talks and many of the workshops of GR17. What especially distinguishes the works presented in this workshop is the predominance of ideas and tools from partial differential equation theory, and the focus on their application to questions arising in classical general relativity.

Over 100 abstracts were submitted to the A3 workshop. Of these, 36 were chosen for oral presentation, and a number of the rest were chosen for the poster sessions. In this review, we discuss some of the more interesting results which those attending the Workshop on Mathematical Studies of the Field Equations learned about.

The oral presentations of the Workshop A4 on Analytic Approximation and Perturbation Methods are summarised. Topics covered include post-Newtonian approximations, radiation reaction in general relativity, post-Minkowskian approximations, rotational perturbations, black hole perturbations and quasi-normal modes, Efroimsky formalism, background independent gravitational waves and cosmological perturbations.

No abstract received.

No abstract received.

Session B1 hosted a number of talks on recent studies and results that provide new exciting perspectives in the field of Relativistic Astrophysics and Cosmology. A brief summary of the session is presented here.

No abstract received.

The “Late Universe and Gravitational Lenses” session featured a broad spectrum of talks, with topics ranging from the cosmic microwave background to the density profiles of dark matter halos, and from perturbation theory to cosmic topology. The common thread through all of the talks was the way general relativity impacts our current understanding of cosmology. As GR forms the underpinning of our cosmological standard model, seemingly abstract and abstruse relativity questions can often yield important cosmological insights.

No abstract received.

We summarize recent progresses in understanding physical mechanisms responsible for gravitational-wave emission in a variety of astrophysical sources, and statistical strategies which have been developed to detect gravitational waves both with ground- and space-based detectors.

No abstract received.

The workshop session C1ii was focused on the results of recent operating detectors. 10 speakers presented the latest results of each experiments: ALLEGRO, GEO, LIGO, TAMA and VIRGO experiments. There were reports about searches for gravitational waves in analysis of observation data. The results are of no detection of gravitational waves, but observational upper-limits of gravitational waves are improved.

The session on advanced detector research and development was principally focused on ideas and experiments investigating the reduction of thermal noise in suspensions and test masses for interferometric gravitational wave detectors. Recurring themes were the potential use of silicon, cryogenic operation, and methods of fabricating suspensions. With respect to the optical design of future detectors, we learnt about the potential advantages of using non-Gaussian beams, the possibility of optimizing signal-to-noise ratio by tuning the signal recycling cavity, and recent results on squeezing light at frequencies of interest for gravitational wave detection. We look forward to seeing many of these innovative ideas incorporated in future detectors.

No abstract received.

Experimental and observational tests of gravity are important in the search for physics beyond General Relativity and the Standard Model and to understand new cosmological findings. Summaries of the talks given in session C2 at GR17 in Dublin in July of 2004 are presented.

No abstract received.

No abstract received.

As long as the back reaction of quantum fields on the spacetime metric can be ignored, quantum field theory on a curved background is an excellent approximation to a theory combining quantum effects with gravitational interactions. Famous predictions have been obtained in this framework, in particular Hawking’s prediction of thermal radiation of black holes [16] and Unruh’s prediction of a thermal environment experienced by an accelerated observer [29]. In the topical session of GR17 on this theory three main subjects were discussed, namely the construction of interacting fields by renormalized perturbation theory, the construction of analogous models for gravitational interactions and the rôle of fluctuations of the energy momentum tensor.