Gravitational waveforms from binaries in higher-derivative gravity: a Love story

Abstract

We study the emission of gravitational waves by a test particle orbiting a non-rotating black hole in higher-derivative gravity theories with cubic and quartic contractions of the Riemann tensor. To this aim, we first derive the master equations describing even- and odd-parity perturbations in the presence of an arbitrary source term, and then construct a Post-Minkowskian expansion of the solutions to the homogeneous master equations. Specializing to a circular binary system, we compute the Post-Newtonian expansion of the waveform, as well as the energy and angular-momentum fluxes at infinity. We show that higher-derivative corrections to the waveform and to the fluxes always appear at 5PN order, and are universally proportional to the Love number describing the deformability of the geometry under the $\ell=2$ mode perturbation. These analytical results are validated against numerical computations, which also allow us to extend the analysis to larger velocities.