Physics
Permanent URI for this communityhttp://hdl.handle.net/1903/2269
Browse
3 results
Search Results
Item Novel Techniques for Simulation and Analysis of Black Hole Mergers(2011) Boggs, William Darian; Tiglio, Manuel; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation consists of three research topics from numerical relativity: waveforms from inspiral mergers of black hole binaries, recoils from head-on mergers of black holes, and a new computational technique for error-reduction. The first two topics present research from journal articles that I coauthored with my colleagues in the NASA Goddard Numerical Relativity research group. Chapter 2 discusses a heuristic model of black hole binary mergers and the waveforms produced by them, based on simulations of nonspinning black holes. The gravitational radiation is interpreted as the result of an implicit rotating source that generates the radiation modes as the source multipoles rotate coherently. This interpretation of the waveform phase evolution provides a unified physical picture of the inspiral, plunge, and ringdown of the binaries, and it is the basis of an analytic model of the late-time frequency evolution. Chapter 3 presents a study of kicks in head-on black hole mergers, emphasizing the distinct contributions of spin and mass ratio, as well as their combined effects, to these radiation-induced recoils. The simpler dynamics of head-on mergers allow a more clear separation of the two types of kick and a validation of post-Newtonian predictions for the spin scaling of kicks. Finally, Chapter 4 presents a technique I developed to improve the accuracy of the field evolution in numerical relativity simulations. This "moving patches" technique uses local coordinate frames to minimize black hole motion and reduce error due to advection terms. In tests of the technique, I demonstrate reduction in constraint violations and in errors in the orbital frequency derived from the black holes' motions. I also demonstrate an accuracy gain in a new diagnostic quantity based on orbital angular momentum. I developed this diagnostic for evaluating the moving patches technique, but it has broader applicability. Though the moving patches technique has significant performance costs, these limitations are specific to the current implementation, and it promises greater efficiency and accuracy in the future.Item How to Prove a Differential Form of the Generalized Second Law(2011) Wall, Aron Clark; Jacobson, Theodore A; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A new method is given for proving the semiclassical generalized second law (GSL) of horizon thermodynamics. Unlike previous methods, this method can be used to prove that entropy increases for arbitrary slices of causal horizons, even when the matter fields falling across the horizon are rapidly changing with time. Chapter I discusses how to define the GSL, and critically reviews previous proofs in the literature. Chapter II describes the proof method in the special case of flat planar slices of Rindler horizons, assuming the existence of a valid renormalization scheme. Chapter III generalizes the proof method to arbitrary slices of semiclassical causal horizons, by the technique of restricting the fields to the horizon itself. In the case of free fields it is clear that this restriction is possible, but for interacting fields the situation is murkier. Each of the three parts has been, or will be, separately published elsewhere.Item SELF-FORCE AND NOISE-KERNEL IN CURVED SPACE-TIME USING QUASI-LOCAL EXPANSION METHODS(2007-04-29) Eftekharzadeh, Ardeshir; Hu, Bei-Lok B; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We find a quasi-local expansion for the tail term of the Green's function for a particle with scalar charge moving outside the event horizon of a black hole of mass M. To do that we use a WKB-like ansatz for the mode functions and we solve the resulted differential equation by iteration. We then sum the mode contributions using Plana sum rule. The fact that we find the tail term as an analytic expression is important. We then use our expressions to calculate the self-force exerted upon a particle of scalar charge that has been held at rest from infinite past to some time after which it moves on a general geodesic of the space-time. We perform this computation first for the radial path of a particle released from rest and then generalize the method for a particle launched on a general geodesic. We then turn to computing the noise kernel. The problem we are primarily concerned with is that of a massless, conformally coupled scalar field in the optical Schwarzschild (the ultrastatic spacetime conformal to the Schwarzschild black hole). In contrast to previous work done on this topic, we keep the two points separate, and as a result work with non-renormalized Wightman functions. We give an expression in terms of an expansion in coordinate separation and conclude with an outlook.