Improved gravitational-wave constraints on higher-order curvature theories of gravity

TL;DR

This study uses gravitational wave data to place new constraints on certain modified gravity theories, notably tightening bounds on Einstein-dilaton-Gauss-Bonnet gravity, while finding limited constraints on dynamical Chern-Simons gravity.

Contribution

The paper provides the first robust gravitational wave constraints on Einstein-dilaton-Gauss-Bonnet gravity using multiple events, and demonstrates the robustness of these bounds against various modeling uncertainties.

Findings

Constraint on Einstein-dilaton-Gauss-Bonnet coupling: √α_{EdGB} < 1.7 km

No meaningful constraints on dynamical Chern-Simons gravity

Bounds are robust to waveform model choices and higher-order effects

Abstract

Gravitational wave observations of compact binaries allow us to test general relativity (and modifications thereof) in the strong and highly-dynamical field regime of gravity. Here we confront two extensions to general relativity, dynamical Chern-Simons and Einstein-dilaton-Gauss-Bonnet theories, against the gravitational wave sources from the GWTC-1 and GWTC-2 catalogs by the LIGO-Virgo Collaboration. By stacking the posterior of individual events, we strengthen the constraint on the square root of the coupling parameter in Einstein-dilaton-Gauss-Bonnet gravity to $\sqrt{\alpha_{\rm \tiny EdGB}} < 1.7$ km, but we are unable to place meaningful constraints on dynamical Chern-Simons gravity. Importantly, we also show that our bounds are robust to (i) the choice of general-relativity base waveform model, upon which we add modifications, (ii) unknown higher post-Newtonian order terms in the modifications to general relativity, (iii) the small-coupling approximation, and (iv) uncertainties on the nature of the constituent compact objects.