Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session C12: Self-force Calculations and their Implications for Gravitational Physics |
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Sponsoring Units: GGR Chair: Eric Poisson, University of Guelph Room: Royal CD |
Saturday, April 30, 2011 1:30PM - 1:42PM |
C12.00001: The effective source approach to the self-force problem Peter Diener, Ian Vega, Barry Wardell Extreme Mass Ratio In-spirals of compact objects into super massive black holes are expected to be a very important source of gravitational waves for LISA. Traditionally perturbation techniques have been employed to analyze such sources. Here the small compact object is treated as a point particle moving on a perturbed geodesic in an exact black hole spacetime. Gravitational waves are emitted due to the particle motion which are then back scattered off the curvature of the background space-time and interact with the particle itself at a later point in the orbit: The so called self-force problem. In these approaches the field equations have been evolved with a singular delta-source, yielding a singular field at the location of the particle. To calculate the self-force the singular field then has to be carefully subtracted. Recently a new approach have been proposed where the singularity of the point particle is subtracted from the source before the evolution is done, resulting in a regular field at the particle location from which the self-force can easily be calculated. I will report on the progress on a numerical implementation of this approach applied to a scalar charge moving in orbit around a Schwarzschild black hole. [Preview Abstract] |
Saturday, April 30, 2011 1:42PM - 1:54PM |
C12.00002: Gravitational self-force in a radiation gauge for a particle in circular orbit around a Kerr black hole Abhay Shah, Tobias Keidl, John Friedman, Larry Price This talk reports recent progress on computing the self-force in a radiation gauge for a particle in circular orbit around a Kerr black hole. We work in a gauge which allows us to use the Teukolsky equation to obtain retarded field needed to compute the self-force. We use of the Chrzanowski-Cohen-Kegeles formalism to extract the perturbed metric from the Weyl scalar. The Hertz potential is calculated by algebraically inverting the differential angular equation relating it to the Weyl scalar. Since this is an algebraic inversion, every operator acting on the Hertz potential to yield the self-force can be traced back to an action on the Weyl scalar, which simplifies our analytic work. Once the retarded self-force is calculated, we match it numerically to an appropriate series in the angular harmonic index l to extract regularization parameters. The quantity $h_{ab}u^a u^b$ and an associated change in the orbital frequency are invariant under helically symmetric gauge transformations, and we compute them inside the (Boyer-Lindquist) radius of the particle. [Preview Abstract] |
Saturday, April 30, 2011 1:54PM - 2:06PM |
C12.00003: Filling in the missing pieces in a radiation-gauge self-force calculation John Friedman, Tobias Keidl, Abhay Shah When computing the self force in a radiation gauge, one needs separately to compute the nonradiative contributions: These arise from the change in the mass and angular momentum of the spacetime and from a discontinuous gauge transformation associated with a change in the center of mass. In a Schwarzschild background these are easily distinguished as the l=0 and l=1 parts of the perturbed metric. In a Kerr background, additional subtleties arise from the fact that the perturbed field equations mix different values of l and, for generic orbits, from the fact that angular and time harmonics of a point-particle source are nonzero in the region between periastron and apastron. The talk presents ways to handle each of these difficulties. [Preview Abstract] |
Saturday, April 30, 2011 2:06PM - 2:18PM |
C12.00004: Gauge, Averaging, Parity, and Modesum Regularization in Gravitational Self-force Samuel Gralla Previous treatments of gravitational self-force have relied on Lorenz-gauge Hadamard techniques (involving lengthy calculations) for both the derivation and the expression of the final result. I give a short derivation that nowhere involves the Lorenz gauge and that leads to an angle-average formula for the self-force that holds in any admissible gauge. For gauges that satisfy a parity condition given by Regge and Teitelboim to ensure that their Hamiltonian center of mass is well-defined, the result simplifies to a simple average of the bare force. Remarkably, the parity condition also allows one to show that all such gauges share the same ``mode sum regularization parameters''. Since both the Lorenz gauge and a radiation gauge of Kerr (Keidl,Shah,Friedman,Kim,Price) satisfy the parity condition, existing Lorenz-gauge mode sum regularization results may be employed in radiation gauge calculations. [Preview Abstract] |
Saturday, April 30, 2011 2:18PM - 2:30PM |
C12.00005: The innermost stable circular orbit and its shifts due to conservative forces Marc Favata The innermost stable circular orbit (ISCO) of a black hole spacetime denotes the boundary between the stable circular orbits of a test-mass and those that plunge into the event horizon. For geodesic orbits the location of the ISCO is well known in the Schwarzschild and Kerr spacetimes. If conservative forces act on the test-mass, they will shift the location (and frequency) of the ISCO. For the conservative piece of the gravitational self-force, this shift has been calculated by Barack and Sago. I will discuss a similar shift in the ISCO caused by the spin-curvature coupling force on a spinning test-mass. I will also discuss a particular condition for the ISCO that, although derived from the unmodified post- Newtonian equations of motion, is able to exactly reproduce the Kerr ISCO and the ISCO shift due to a spinning test-mass. This condition also closely approximates the Barack-Sago conservative self-force ISCO shift. It is not clear why an ISCO condition derived from approximate post-Newtonian equations is able to accurately reproduce strong-field results. [Preview Abstract] |
Saturday, April 30, 2011 2:30PM - 2:42PM |
C12.00006: Waveforms from a gravitational self--force driven orbital evolution: quasi-circular Schwarzschild orbits Kristen A. Lackeos, Lior M. Burko, Gaurav Khanna We evolve an extreme-mass-ratio binary for the specific case of quasi-circular Schwarzschild orbits, driving the orbital evolution with the full gravitational self force, including both its dissipative and conservative components. The orbital evolution is done in two methods: first by direct integration of the self force, and second by the method of osculating geodesics. When the conservative piece of the self force is artificially set equal to zero we find excellent agreement with results obtained with the usual energy balance approach. For the full gravitational self force we find the dephasing and other effects of the waveform. [Preview Abstract] |
Saturday, April 30, 2011 2:42PM - 2:54PM |
C12.00007: Electromagnetic self-force as a cosmic censor Peter Zimmerman, Ian Vega, Eric Poisson Hubeny identified a scenario in which a charged particle falling toward a near-extreme Reissner-Nordstrom black hole can penetrate the black hole and drive it beyond the extremal limit, thereby giving rise to an apparent violation of cosmic censorship. A version of this scenario, relevant to a Kerr black hole and involving a particle with orbital and/or spin angular momentum, was recently examined by Jacobson and Sotiriou (following up on earlier work by Hod); here also the black hole is driven beyond the extremal limit. The Hubeny analysis was inconclusive, however, because in her scenario the particle crosses the horizon with a near-vanishing acceleration; the test-body acceleration is of the same order of magnitude as the acceleration produced by the particle's own electromagnetic self-force, which was not incorporated in the analysis. In this talk we report on our computation of the electromagnetic self-force acting on a charged particle falling radially toward a Reissner-Nordstrom black hole, and we reveal whether the self-force acts as a cosmic censor by preventing the particle from reaching the event horizon. [Preview Abstract] |
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