The Gulf Coast Meetings started in Brownsville two years ago, and as Richard Price reported back then [1] they were designed to bring together the growing number of relativists in the gulf coast region of the country.
The 3rd Gulf Coast Gravity meeting took place at the University of Alabama in Huntsville on January 23-24 (2007), and was hosted by Lior Burko. Financial support was generously provided by the Physics Department at UAH. The meeting would not have been possible without support from Cindi Brasher and Dora Wynn, and assistance by the UAH Society of Physics Students. Huntsville (``the rocket city'') features the NASA-Marshall Space Flight Center, which makes for a good visit after a meal at any one of the several very nice restaurants scattered through downtown or University Avenue.
The meeting consisted of short, 12 min talks with particular emphasis on student presentations (there is an APS sponsored GGR Prize for the best student talk) and quick overviews of some recent developments. Important breakthroughs in numerical relativity have led to a flurry of activity in the field, and most presentations focused on numerical relativity and on gravitational wave emission.
The conference opened with Michael Watson describing progress in simulating jet formation with particle-in-cell codes [2], using the Kerr geometry as a fixed background. Preliminary results show that a jet is formed. Further details, such as Lorentz-factors and jet distribution dependence on the model parameters will be dealt with in the future. Alan Farrell described recent progress in understanding the numerical instabilities affecting some of the codes for neutron star structure. Preliminary results for isolated neutron stars are encouraging, generalization to more complex systems such as binaries is in progress. Peter Diener made a concise summary [3] of recent work on kicks from generally spinning binaries. He explained the importance of having accurate estimates for the kick velocity from black hole mergers, and how crucial these numbers may be for our understanding of galactic evolution. Enrique Pazos talked about the influence of the background spacetime on the accuracy of wave extraction [4], and particularly about the effect of extraction radius on the measured waveforms. He exemplified the problem with Gaussian wave pulses scattering off a Schwarzschild black hole, both in a linear and non-linear analysis. Arunava Roy described how unification of gravity with electroweak forces may be achieved in extra-dimensional scenarios. In this eventuality, black holes may be created in particle accelerators and cosmic rays, and their signatures can be studied in detail using GROKE [5], a Monte-Carlo generator for black hole production. Miguel Megevand implemented a theoretical model for a scalar field to try to mimic accreting systems. A model with a non-trivial position-dependent potential displays some of the expected features of accreting systems.
The first talk of the afternoon session began with Richard Price exposing some of the contradictions in the literature on late-time tails in the Kerr geometry. He proceeded by showing how mode coupling can be understood already at the linearized level as a second order effect in the rotation parameter, and how this may reconcile the existing contradictory results. Following on Richard's talk, Carl Blaksley described his recent results on tails in the vicinities of extreme charged black holes, and how they differ from previous predictions. The non-triviality of these results follows from the special behavior of the effective potential for wave propagation near the horizon. Manish Jadhav reported on progress to understand how well LISA performs at doing black hole spectroscopy. In particular he's focusing on computing signal-to-noise ratios as a function of source location in the sky, using a Markov Chain Monte Carlo generator. Yasushi Mino reviewed the present status of radiation reaction and self-force on curved backgrounds [6], of particular interest for extreme-mass ratios inspirals. He explained how to resolve some discrepancies and conceptual obstacles in understanding the self-force, and how to proceed in the quest for a logical basis for self-force calculations. In the final talk of the first day, Scott Hawley reported on his recent results [7] concerning initial data for spinning black holes and their interpretation via classical results. An enlarged parameter survey, pushing the separation of the holes to larger values, will possibly clarify some of the remaining issues.
The first day closed with the award of the prize for the best student talk to Enrique Pazos, for his presentation ``The effects of the background geometry on the extracted waveforms''. Congratulations Enrique!
The second day of the meeting opened with Marco Cavaglià showing how uniform motion generates gravitational radiation in braneworld scenarios. This effect may lead to potentially observable consequences [8], such as energy loss by cosmic rays and a stochastic background of gravitational radiation. Pedro Marronetti continued Diener's kick talk to show us that results displaying massive kicks with optimally aligned spin are solid ones [9], in the sense that deviations from initial data producing the largest kicks still produces large kicks. Pedro stressed the need to have an understanding of the astrophysically relevant spin distributions in binaries; this will eventually determine whether or not large kick velocities are common. The good news is that the computational power to perform some of these calculations is modest. Yes, you can try this at home! I presented recent results on unequal-mass mergers of black hole binaries [10], and discussed the nature of the waveforms. I tried to convince the audience that most of the waveform is well understood: the PN approximation describes very well the inspiral almost all the way to the formation of a common apparent horizon, and ringdown describes extremely well the last part. The results show that black hole spectroscopy is possible and also that we are ready to start building realistic templates for the detection of gravitational waves from binary inspiral. Chris Beetle elaborated on an interesting alternative to Post-Minkowskian expansions, the Periodic Standing-Wave Approximation [11], specifically designed to handle periodic systems such as appropriately spaced binaries. He explained the similarities between these two methods and the advantage of having alternatives which can be implemented numerically to all orders. Our host Lior Burko presented results for a time-domain implementation of Teukolsky equation with a delta-like source term [12]. He emphasized the need to have credible alternatives to the well-established frequency-domain methods, and presented in detail results for particles in eccentric and parabolic orbits around rotating black holes. Brett Bolen showed us how to obtain consistent cosmologies in extra-dimensional scenarios with Gauss-Bonnet terms [13], where the size of the extra dimensions is a time-varying function. In this model, corrections to the usual FRW cosmology are consistent with a dark energy equation of state. Closing the meeting, Ruslan Vaulin explained how to use the trace anomaly to compute consistently the stress energy tensor of quantum fields in black hole spacetimes [14]. Ruslan presented several instances of this computation, showing how to obtain non-divergent renormalized stress-energy tensors throughout the spacetime, and how well this method compares to other alternative methods.
The 4th Gulf Coast Gravity Meeting will be held at the University of Mississippi in Oxford, MS. We hope to see you all there!