Speaker
Description
Gravitational-wave observations provide a powerful probe of gravity in the strong-field regime, particularly through the ringdown phase of binary black hole mergers, where the signal is governed by damped quasinormal modes. Recent progress has extended quasinormal-mode calculations beyond general relativity using the modified Teukolsky formalism and spectral methods in several theories, including higher-derivative gravity, scalar Gauss-Bonnet gravity, and dynamical Chern-Simons gravity. In theories such as scalar Gauss-Bonnet and dynamical Chern-Simons gravity, additional scalar degrees of freedom couple to spacetime curvature and generically break isospectrality, so that odd- and even-parity modes acquire different oscillation frequencies and damping times. In this talk, I will discuss how this breaking of isospectrality imprints itself on gravitational-wave observables, and more broadly how the extra degrees of freedom modify the ringdown signal. I will show that isospectrality breaking can induce a characteristic beating pattern in the plus and cross polarization modes. These effects have important implications for waveform modelling in beyond-GR theories and for strong-field tests of general relativity.