Can We Detect Deviations from Einstein's Gravity in Black Hole Ringdowns?

TL;DR

This paper investigates whether deviations from Einstein's gravity can be detected in black hole ringdowns by analyzing quasinormal modes, concluding that higher derivative gravity effects are negligible or suppressed, thus aligning with Einstein's predictions.

Contribution

The paper provides causality-based arguments showing that higher derivative gravity theories do not significantly alter black hole quasinormal modes, supporting Einstein's gravity as the dominant description.

Findings

Higher derivative gravity effects on quasinormal modes are negligible.

Causality constraints limit deviations from Einstein's gravity.

Schwarzschild and Kerr black hole spectra are consistent with Einstein's theory.

Abstract

The quasinormal mode spectrum of gravitational waves emitted during the black hole ringdown relaxation phase, following the merger of a black hole binary, is a crucial target of gravitational wave astronomy. By considering causality constraints on the on-shell graviton three-point couplings within a weakly coupled gravity theory, we present arguments indicating that the contributions to the physics of linear and quadratic quasinormal modes from higher derivative gravity theories are either negligible or vastly suppressed for Schwarzschild and Kerr black holes. Their spectrum and interactions are dictated solely by Einstein's gravity.