Gravitational-Wave Ringdown Through The Black Hole S-Matrix

Speaker
Date
Time
Place
Room 7S1 (Cosmology Hall)
Abstract
After the merger of a binary black hole system, the remnant black hole undergoes free oscillations, emitting gravitational waves known as the ringdown signal. These ringdown waveforms contain multiple quasi-normal modes (QNMs), and it is expected that black hole spectroscopy—resolving these modes individually—will enable tests of gravity in the strong-field regime. However, extracting multiple QNMs from the ringdown requires fitting many parameters, which poses significant challenges for data analysis. In this talk, I will show that the interference pattern among QNMs exhibits universal features, which can be naturally described in terms of the black hole S-matrix or greybody factors. The black hole S-matrix, in particular, provides a compact characterization of the excitation and interference of many QNMs using only a few parameters, especially when the ringdown is sourced instantaneously. In this sense, the black hole S-matrix may be regarded as encoding the universal features of black hole QNM excitations.
Biography
Naritaka Oshita is an Assistant Professor at the Yukawa Institute for Theoretical Physics (Kyoto) working on gravity, cosmology, and quantum field theory.