Implications of the quantum nature of the black hole horizon on the gravitational-wave ringdown

TL;DR

This paper explores how quantum effects at the black hole horizon can alter gravitational-wave signals, leading to reflective boundary conditions, modified quasi-normal modes, and potential echoes in postmerger signals.

Contribution

It introduces a semiclassical membrane model with quantum-induced reflectivity at the horizon, extending the membrane paradigm to include quantum effects and deriving new boundary conditions.

Findings

Quantum horizon effects cause partial reflectivity and frequency-dependent boundary conditions.

Modified quasi-normal mode spectrum with potential gravitational-wave echoes.

Implications for quantum-corrected black hole models and gravitational-wave observations.

Abstract

Motivated by capturing putative quantum effects at the horizon scale, we model the black hole horizon as a membrane with fluctuations following a Gaussian profile. By extending the membrane paradigm at the semiclassical level, we show that the quantum nature of the black hole horizon implies partially reflective boundary conditions and a frequency-dependent reflectivity. This generically results into a modified quasi-normal mode spectrum and the existence of echoes in the postmerger signal. On a similar note, we derive the horizon boundary condition for a braneworld black hole that could originate from quantum corrections on the brane. This scenario also leads to a modified gravitational-wave ringdown. We discuss general implications of these findings for scenarios predicting quantum corrections at the horizon scale.