Constraints on Einstein-dilaton-Gauss-Bonnet gravity from Black Hole-Neutron Star Gravitational Wave Events

TL;DR

This study uses recent gravitational wave data from neutron star-black hole binaries to place new, tighter constraints on Einstein-dilaton Gauss-Bonnet gravity, testing its viability in strong-field regimes.

Contribution

The paper provides the first bounds on the coupling constant of Einstein-dilaton Gauss-Bonnet gravity using neutron star-black hole mergers and incorporates higher post-Newtonian corrections for improved accuracy.

Findings

Derived a 90% credible upper bound of rac{_{GB}}{ ext{km}} blesssim 1.33

Combined multiple GW events to tighten the bound to rac{_{GB}}{ ext{km}} blesssim 1.18

Higher post-Newtonian corrections improve bounds by up to 14.5%

Abstract

Recent gravitational wave observations allow us to probe gravity in the strong and dynamical field regime. In this paper, we focus on testing Einstein-dilaton Gauss-Bonnet gravity which is motivated by string theory. In particular, we use two new neutron star black hole binaries (GW200105 and GW200115). We also consider GW190814 which is consistent with both a binary black hole and a neutron star black hole binary. Adopting the leading post-Newtonian correction and carrying out a Bayesian Markov-chain Monte Carlo analyses, we derive the 90\% credible upper bound on the coupling constant of the theory as $\sqrt{\alpha_{GB}} \lesssim 1.33\,\rm km$, whose consistency is checked with an independent Fisher analysis. This bound is stronger than the bound obtained in previous literature by combining selected binary black hole events in GWTC-1 and GWTC-2 catalogs. We also derive a combined bound of $\sqrt{\alpha_{GB}} \lesssim 1.18\,\rm km$ by stacking GW200105, GW200115, GW190814, and selected binary black hole events. In order to check the validity of the effect of higher post-Newtonian terms, we derive corrections to the waveform phase up to second post Newtonian order by mapping results in scalar-tensor theories to Einstein-dilaton Gauss-Bonnet gravity. We find that such higher-order terms improve the bounds by $14.5\%$ for GW200105 and $6.9\%$ for GW200115 respectively.