The 7th Eastern Gravity Meeting

Deirdre Shoemaker, Cornell deirdre-at-astro.cornell.edu
The seventh annual Eastern Gravity meeting took place on the lovely campus of Bowdoin College in Brunswick, Maine from June 11-12, 2004. Approximately thirty relativists participated in the conference.

In the first session, talks of the current status of evolving binary black hole orbits in the fully-non-linear regime were discussed. Gregory Cook (Wake Forest University) started the meeting by relating the current state of efforts to generate astrophysically realistic initial data for black-hole binaries. In particular, he discussed the consequences of different boundary conditions on the data. Ulrich Sperhake (Penn State) presented evolutions using dynamical excision with fixed mesh refinement and the BSSN-formulation. He pointed out that there are still difficulties in evolving a boosted black hole with moving excision regions; nonetheless, he has been able to evolve black holes with boosted velocities of 0.4c for 120M. Wolfgang Tichy (Penn State) showed numerical simulations of a black hole binary quasi-circular orbit also using BSSN and fixed mesh refinement. He emphasized the importance of using the gauge to keep the apparent horizons in a fixed location long enough to evolve one orbital time period. Carlos Sopuerta (Penn State) ended this session with a new effort to model Extreme-Mass-Ratio Binaries numerically using finite elements. To date they have successfully completed a toy-model using scalar gravity.

The second morning session focused on binaries of a black-hole and a companion star. The first talk was given by Monica Skoge (student at Princeton) a former undergraduate student at Bowdoin. She illustrated a numerical method for the construction of quasi-equilibrium models of black hole-neutron star binaries, concentrating the the construction of such binaries in Newtonian gravity. Thomas Baumgarte (Bowdoin College) continued, focusing on the relativistic version of the problem. In their preliminary work, they located the onset of tidal disruption in this fully relativistic framework in the extreme-mass-ratio regime. Pablo Laguna (Penn State) presented gravitational waves from stellar disruptions by super-massive black holes. He showed that quadrupole gravitational waves emitted during the tidal disruption process are described reasonable well (within $\approx 5\%$) by a point particle approximation even in the strong encounter case. Finally Sasa Ratkovic (graduate student at SUNY at Stony Brook) ended the session with a report on how different equations of state for the companion (either quark or neutron star) may result in a detectable difference in the gravitational wave signatures. These results are based on a pseudo-general relativistic potential that incorporates post-Newtonian corrections.

The third session concerned mostly quantum cosmology. Seth Major (Hamilton College) started off with a discussion on the consequences of a quantum cosmology arising from quantum geometry. Building on the work of Martin Bojowald, he presented the solution to the Lorentzian Hamiltonian constraint for isotropic loop quantum cosmology coupled to a massless scalar field. David Craig (Hamilton College) discussed decoherent histories formulations of quantum theory and described applying these ideas to construct a consistent quantum theory of recollapsing homogeneous universes, the Bianchi IX cosmological models. Michael Pfenning (U.S. Military Academy) gave a brief introduction to the quantum weak energy inequalities and showed ways the quantum inequalities can by used to constrain the magnitude of the Casimir vacuum energy density both above and below. Daniel Cartin (Naval Academy Preparatory School) followed recent work by Bojowald and others that looked at cosmological models in terms of loop quantum gravity and applied these methods to Bianchi I LRS spacetimes.

The final session of the day started with a discussion on self-force effects on the ISCO of Schwarzschild by Steve Detweiler (University of Florida). The self-force effects, from a scalar field, have been calculated for a particle in a circular orbit of the Schwarzschild geometry. Such effects change the radius and orbital frequency of the innermost stable circular orbit. Steve Drasco (graduate student at Cornell) computed gravitational waveforms, and asymptotic fluxes of energy and angular momentum produced by a spin-less point particle moving along an arbitrary bound geodesic of a Kerr black hole accurate to the first order in the mass ratio of the two bodies. Etienne Racine (graduate student at Cornell) presented a surface integral derivation of post-1-Newtonian translational equations of motion for a system of arbitrarily structured bodies, including the coupling to all the bodies' mass and current multi-pole moments.

The second day of the conference started with Charles Evans (University of North Carolina) presenting a means of specifying exact outgoing-wave boundary conditions in time domain calculations with the boundary at a finite distance from the isolated source. He applied the method to the cases of a flat-space three-dimensional wave equation and Schwarzchild. Ian Morrison (undergraduate, Bowdoin College) described the effects of differential rotation on the maximum mass of Neutron Stars with nuclear equations of states. He finds that the maximum mass increases above the limit for non-rotating stars by about 50$\%$. David Garfinkle (Univ. of Guelph/Perimeter Institute) showed the results for the numerical simulation of the approach to the singularity in a general (no symmetry) vacuum spacetime, results support the BKL conjecture; namely, as the singularity is approached spatial derivatives become negligible and at each spatial point the dynamics becomes that of a homogeneous, oscillatory spacetime. Steven Liebling (Long Island University) discussed his use of non-gravitating, nonlinear models in three dimensions using a distributed adaptive mesh refinement framework to investigate the threshold behavior as a step in developing the infrastructure to model the gravitational field equations.

The final session of the meeting began with Munawar Karim (St. John Fisher College) who presented his work on a compact (10cm) gravitational wave detector. Eanna Flanagan (Cornell) discussed how, when a source emits a burst of gravitational waves, different observers will measure different net changes in the angular momentum of the source, an effect related to the phenomenon of gravitational wave memory. Douglas Sweetser presented a Rank 1 Unified Field Theory. He contends that it may be possible to quantize the 4D field equations using two spin fields: spin 1 for EM and spin 2 for gravity. R.L. Collins (retired, The Univ. Texas at Austin) presented his case for a scalar alternate to GR based on Mass-metric relativity. He contends that the Gravity Probe B will potentially invalidated one of these theories of gravity.

On behalf of the participants, congratulations again to Steve Drasco for winning the Best Student Talk award. All the students gave outstanding talks, congratulations to each of them. Our thanks to Thomas Baumgarte and Bowdoin College for organizing a well run, enjoyable meeting and reception. Greg Cook has volunteered to host the 8th Eastern Gravity meeting next year at Wake Forest University in North Carolina, date to be announced.


Jorge Pullin 2004-09-10