Enrico Cannizzaro "Unveiling the Early Ringdown: Prompt Response of a Schwarzschild Black Hole "

Wednesday 25 Feb 2026, 12:30 → 14:30 Europe/Rome

Sala Lauree (Marconi Building) (La Sapienza)

The gravitational waveform emitted by a binary black-hole merger is usually divided into three phases: inspiral, merger, and ringdown. While accurate analytical descriptions exist for the inspiral and the late stationary ringdown, the transient signal connecting them remains poorly understood from first principles.

In this talk I will study an early ringdown contribution commonly referred to as prompt response: the part of the perturbation propagating along the curved light cone before the onset of stationary ringing. Using a post-Minkowskian expansion of the Schwarzschild Green’s function, I will show that the prompt response arises from the residue of a pole at zero frequency in the complex Fourier plane. This demonstrates that the prompt signal is a low-frequency effect, contrary to the common intuition associating it with high-frequency arcs.

I will compare the analytic prediction with numerical evolutions, showing good agreement for distant sources and discussing phenomenological corrections required closer to the black hole. These results represent a step toward an analytic description of the plunge–merger waveform.