Department of Physics and Astronomy

University of Mississippi

Events

Event Information:

  • Tue
    07
    Mar
    2017

    Colloquium: Three Talks on General Relativity

    4:00 pmLewis Hall 101

    Seth Hopper
    Gravitation in Técnico
    Instituto Superior Técnico — Portugal

    Bound and Unbound Motion Around Static Black Holes

    A massive two-body system will interact gravitationally. Depending on the velocities and separation of bodies, their motion may be bound and periodic (as in the Earth-Sun system) or unbound (like a comet that passes the Sun only once). General relativity predicts that each of these systems will radiate energy in the form of gravitational waves. However, the qualitative difference between the systems implies that different techniques must be used to analyze them. In this talk I will briefly introduce the mathematical theory behind gravitational radiation of two body systems (specifically in the extreme mass-ratio regime) and consider how one can efficiently compute that radiation for different classes of problems.

     

    Andrea Nerozzi
    Gravitation in Técnico
    Instituto Superior Técnico — Portugal

    The Problem of Gauge Fixing in the Newman-Penrose Formalism

    Since its introduction the Newman-Penrose formalism has been widely used in analytical and numerical studies of Einstein's equations, like for example for the Teukolsky master equation, or as a powerful tool for wave extraction in numerical relativity. The problem of gauge fixing, or more specifically, tetrad fixing is however still debated and only partially understood when the NP formalism is used to extract gravitational waves from numerical simulations.

    In this talk I will approach the whole formalism with the goal of finding an invariant expression for all the variables in the NP formalism, namely Weyl scalars and the spin coefficients, once a specific yet generally defined tetrad is chosen.I will show that it is possible to do so, and give a general recipe for the task, as well as an indication of the quantities and identities that are required. The applications and importance of this approach to the problem of wave extraction in numerical relativity will be discussed.

    Laura Bernard
    Gravitation in Técnico
    Instituto Superior Técnico — Portugal

    Dynamics of Compact Binary Systems at the Fourth Post-Newtonian Order

    Templates of coalescing compact binaries' gravitational waveform are used for the detection and precise determination of the physical parameters of gravitational waves by the current and next generations of interferometric detectors. In order to compute the waveform with high accuracy, the dynamics of compact binary systems should be known to the same precision. In this talk, I will address the question of the dynamics of non-spinning compact binary systems at the fourth post-Newtonian order in harmonic coordinates. I will present a method based on a Fokker action adapted to the specificities of the post-Newtonian formalism, including the so-called tail effects which appear for the first time in the conservative dynamics at 4PN. I will then derive the energy and periastron advance for circular orbits and show a full agreement with previous results from gravitational self-force calculations.