GRASS Seminar: Black hole ringdown in higher-derivative gravity

After a perturbation, black holes emit gravitational radiation at certain characteristic frequencies corresponding to their quasinormal modes (QNMs). These modes depend on the underlying gravitational dynamics and hence their detection in gravitational wave experiments provides an excellent test to look for deviations to Einstein gravity. In the case of Kerr black holes in General Relativity (GR), the study of QNMs is made possible by the Teukolsky equation. However, the study of perturbations of rotating black holes in theories beyond GR is a very challenging problem that has remained elusive for a long time. In this talk I will present a resolution to this problem by introducing (and solving) a "universal" Teukolsky equation that holds in modifications of GR. I will use this equation to obtain the QNM frequencies of black holes with substantial angular momentum in higher-derivative extensions of GR. I will also discuss the case of near-extremal black holes, which poses additional challenges and is the subject of ongoing investigations.