Frequency contamination from new fundamental fields in black hole ringdowns

TL;DR

This work develops a theory-agnostic framework for black hole ringdown beyond General Relativity by deriving a generalized, perturbative structure from modified Teukolsky equations. It shows that deviations manifest as both shifts in GR QNM frequencies and new frequencies associated with extra nonminimally coupled fields, leading to a frequency-contamination effect in the observed waveform. A comprehensive ringdown ansatz is constructed, supported by both top-down and constructive analyses, and the results indicate that the contamination can be as significant as the frequency shifts within realistic coupling regimes. The findings have important implications for gravitational-wave data analysis, urging the inclusion of extra-field frequencies in QNM searches to avoid biased tests of GR and to enable more robust constraints on bGR theories.

Abstract

We revisit the modelling of black hole ringdown beyond General Relativity (GR), emphasizing the limitations of approaches that rely solely on shifted quasinormal mode (QNM) frequencies. Starting from modified Teukolsky equations in such scenarios, we classify the distinct types of deviations that can arise -- those shifting QNM frequencies, and those introducing additional frequencies associated with extra fields. We then construct the most general ansatz for metric perturbations in this context and discuss its implications for QNM modelling and theory-agnostic tests of GR using gravitational wave data.