Theory-agnostic searches of non-gravitational modes in the ringdown

TL;DR

The paper tackles the search for beyond-GR physics in black-hole ringdowns by introducing a theory-agnostic framework that adds test-field, non-gravitational modes to the GR ringdown and focuses on their amplitudes as probes of new couplings. It treats standard Kerr QNM frequencies and damping as fixed at leading order, while allowing extra-mode amplitudes to capture deviations. Applied to O3 events GW150914, GW190521, and GW200129, the method finds no significant evidence for extra modes given current SNR, reinforcing GR predictions. Forecasts for third-generation detectors indicate sensitivities to extra-mode amplitudes around $10^{-2}$, offering stringent tests of beyond-GR couplings and guiding extensions to higher harmonics or specific modified-gravity theories.

Abstract

We present a theory-agnostic framework to search for extra-fundamental modes in the ringdown phase of black hole mergers. These modes, distinct from standard General Relativity (GR) deviations, originate from modifications of the theory of gravity. Applying our method to the events GW150914, GW190521, and GW200129, we find no significant evidence for extra modes beyond those expected in GR.

Figures (1)

• Figure 1: $\log_{10}$ Bayes factors for various ringdown models with extra scalar or vector modes (labelled with 'A') relative to the GR1 model, as a function of the offset time $t_{\rm offset}$. Different colors and line styles denote different events.