8th Capra Meeting on Radiation Reaction

Leor Barack, University of Southampton L.Barack-at-maths.soton.ac.uk
The Capra meetings are annual gatherings of theorist working on the problem of radiation reaction in General Relativity. Previous meetings were held in Southern California (in 1998, at a ranch donated to Caltech by former Caltech alumnus, Hollywood director Frank Capra), Dublin, Caltech, Potsdam (Germany), Penn State, Kyoto, and Brownsville (Texas). The Capra meetings focus on the study of radiation reaction and self interaction (``self force'') in curved spacetime, especially in the context of the general relativistic two-body problem. Recent interest in this problem has been strongly driven by the prospects of detecting gravitational waves from inspirals of compact objects into supermassive black holes, using the planned LISA detector. There has been a remarkable progress over the last few years on the problem of modeling such inspirals, much through the work of the Capra community.

This year's meeting--the eighth in the series--took place July 11-14th in Abingdon (Oxfordshire), UK. Organized jointly by the Southampton Relativity Group (N. Andersson, L. Barack, K. Glampedakis) and the Centre for Fundamental Physics at RAL (R. Bingham), the meeting was hosted at RAL's Cosener's house--a conference facility situated at a picturesque Thames side in the grounds of the medieval Abbey of Abingdon. 41 researchers attended the meeting this year, representing universities in 8 countries. The scientific agenda included 1-hour contributed talks, with a significant portion of the time reserved for questions and discussion. The topics covered ranged from issues in the fundamental formulation of self forces in curved spacetime, through advances in black hole perturbation theory, to actual computations of the self force effect in black hole orbits. The last part of the meeting focused on detection aspects and data-analysis strategies.

The meeting opened with a user-friendly ``self-force primer'' by Steve Detweiler (Gainesville). Eric Poisson (Guelph) followed with a talk on the metric of tidally distorted black holes, and Warren Anderson (Milwaukee) presented results from an analytic computation of the local tail contribution to the gravitational self force. Leor Barack (Southampton) concluded the first day with a talk on the Lorenz-gauge formulation of black hole perturbation theory, with applications to self force calculations. In the second day of the meeting, Dong-Hoon Kim (Gainesville) presented his calculation of the ``regularization parameters'' necessary for calculating the gravitational self-force on particles in circular orbits around Schwarzschild black holes. Steve Detweiler then showed how these can be used to deduce some gauge-invariant self-force effects for such orbits. Hiroyuki Nakano (Osaka City University) next explained how to derive the regularization parameters for generic orbits in Schwarzschild, and was followed by Waratu Hikida (Kyoto), who presented first results from calculations of the scalar self-force for eccentric orbits. Sophiane Aoudia (Nice) discussed the calculation of the regularization parameters in the case of a particle plunging radially into a black hole. A fully-numerical approach to the problem was introduced by Carlos Sopuerta (Penn State), who presented first results from time-domain finite-element numerical simulations of extreme-mass-ratio inspirals.

The third day of the meeting was opened by Carlos Lousto (Brownsville) with a talk on recent progress on the problem of reconstructing the metric perturbation in black hole spacetimes. This was followed up by Bernard Whiting (Gainesville), who discussed further ideas on how one might go about reconstructing the metric perturbation in Kerr spacetime, and by Larry Price (Gainesville) who presented a useful Maple toolkit for carrying out calculations in the GHP approach to Kerr perturbations. Eran Rosenthal (Guelph) wrapped up this part of the meeting with a talk on regularization of the second-order self force.

In opening the final, ``detection aspects'' part of the meeting, Jonathan Gair (Cambridge) presented work done to develop a set of ``quick and dirty'' approximate waveforms for extreme-mass-ratio inspirals, which had been used to scope out data-analysis issues. Norichika sago (Osaka) reviewed the underlying formalism for an alternative set of approximate waveforms, based on a form of adiabaticity assumption and a time-averaging procedure. A numerical code for calculating such adiabatic waveforms was presented by Steve Drasco (Cornell) at the beginning of the last day of the meeting. He argued that such waveforms are likely to be sufficiently accurate to enable detection of extreme-mass-ratio inspirals with LISA, but perhaps not accurate enough to allow full extraction of system parameters. Next, Kostas Glampedakis (Southampton) presented a formalism that could be used to quantify deviations from Kerr geometry, as encoded in the waveforms from extreme-mass-ratio inspirals. Jonathan Gair then discussed the challenges and work done on developing data-analysis techniques for searching over inspirals in the LISA data stream. Gareth Jones (Cardiff) described a search method based on an algorithm for identifying ``clusters and ridges'' on a time-frequency spectrogram. Alberto Vecchio and Alexander Stroeer (Birmingham) presented a data analysis scheme for detecting interacting white-dwarf binaries, with lessons for detection of extreme-mass-ratio inspirals. Finally, Charles Wang (Aberdeen) discussed the consequences of photons interacting with gravitational waves from compact objects.

An electronic version of all talks given in the meeting is available online at http://www.sstd.rl.ac.uk/capra/

The organizers acknowledge the generous financial support of RAL and the IOP Gravitational Physics Group.

Jorge Pullin 2005-10-05