Exceptional Points in Quasinormal Spectra of Hairy Black Holes

TL;DR

This paper identifies an exceptional point in the quasinormal mode spectrum of hairy black holes and demonstrates its significance for more accurate gravitational wave ringdown modeling.

Contribution

It uncovers an exceptional point in black hole spectra and introduces an EP-based model that improves the description of ringdown signals over standard methods.

Findings

EP ansatz captures resonant contributions more naturally.

Standard fits may still show EP features even without explicit modeling.

EP identification enhances understanding of black hole ringdown signals.

Abstract

Exceptional points (EPs) in quasinormal mode (QNM) spectra are non-Hermitian degeneracies at which both the eigenvalues and eigenfunctions coalesce. In this paper, we identify an EP in the scalar QNM spectrum of hairy black holes in the Einstein-Maxwell-scalar theory by scanning the parameter space. We then investigate its implications for ringdown signals by extracting QNMs from time-domain waveforms. Our results show that an EP ansatz, which includes a resonant contribution containing a term linear in time, provides a more robust description of ringdown at the EP than the standard ansatz based on a superposition of independent damped modes. In particular, it captures the resonant contribution associated with spectral coalescence more naturally, and even when the waveform is fitted with the standard ansatz, the resulting fit may still exhibit characteristic features of the EP ansatz.