Black hole-neutron star mergers in Einstein-scalar-Gauss-Bonnet gravity

TL;DR

This study investigates black hole-neutron star mergers within Einstein-scalar-Gauss-Bonnet gravity, revealing that deviations from general relativity mainly cause a faster inspiral and minor effects on the merger gravitational wave signal.

Contribution

First numerical evolution of black hole-neutron star mergers in shift-symmetric Einstein-scalar-Gauss-Bonnet gravity, analyzing gravitational wave and scalar radiation impacts.

Findings

Accelerated inspiral frequency evolution compared to GR.

Minor impact on merger gravitational wave amplitude.

Consistency with post-Newtonian calculations during inspiral.

Abstract

Gravitational wave observations of black hole-neutron star binaries, particularly those where the black hole has a lower mass compared to other observed systems, have the potential to place strong constraints on modifications to general relativity that arise at small curvature length scales. Here we study the dynamics of black hole-neutron star mergers in shift-symmetric Einstein-scalar-Gauss-Bonnet gravity, a representative example of such a theory, by numerically evolving the full equations of motion. We consider quasi-circular binaries with different mass-ratios that are consistent with recent gravitational wave observations, including cases with and without tidal disruption of the star, and quantify the impact of varying the coupling controlling deviations from general relativity on the gravitational wave signal and scalar radiation. We find that the main effect on the late inspiral is the accelerated frequency evolution compared to general relativity, and that--even considering Gauss-Bonnet coupling values approaching those where the theory breaks down--the impact on the merger gravitational wave signal is mild, predominately manifesting as a small change in the amplitude of the ringdown. We compare our results to current post-Newtonian calculations and find consistency throughout the inspiral.