Events
Event Information:

Tue07Mar20174:00 pmLewis Hall 101
Colloquium: Three Talks on General Relativity
Seth Hopper
Gravitation in Técnico
Instituto Superior Técnico — PortugalBound and Unbound Motion Around Static Black Holes
A massive twobody system will interact gravitationally. Depending on the velocities and separation of bodies, their motion may be bound and periodic (as in the EarthSun 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 massratio regime) and consider how one can efficiently compute that radiation for different classes of problems.
Andrea Nerozzi
Gravitation in Técnico
Instituto Superior Técnico — PortugalThe Problem of Gauge Fixing in the NewmanPenrose Formalism
Since its introduction the NewmanPenrose 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 — PortugalDynamics of Compact Binary Systems at the Fourth PostNewtonian 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 nonspinning compact binary systems at the fourth postNewtonian order in harmonic coordinates. I will present a method based on a Fokker action adapted to the specificities of the postNewtonian formalism, including the socalled 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 selfforce calculations.