General Relativity Seminar

Speaker: Ahmed Seta, Harvard University

Title: pp Waves: Quasinormal Modes & Hidden Symmetries of Black Holes

Abstract: The spectrum of quasinormal modes of 4D flat space black holes is not analytically tractable, but there are two asymptotic limits where the QNM spectrum is under control: weak damping and strong damping. In this talk, I will explain how these asymptotic QNMs are controlled by dynamical symmetries of the wave equation in certain kinematic limits.  These two asymptotic limits are, in turn, captured by the two classes of bound null geodesics in the black hole geometry: the photon ring and the horizon. I will also discuss the Penrose limit: a scaling limit into the geometry experienced by these geodesics, which results in a plane-wave spacetime where the dynamical symmetries get enhanced into isometries.