Scalar-Gauss-Bonnet gravity: Infrared causality and detectability of GW observations

TL;DR

This paper explores how scalar-Gauss-Bonnet gravity affects black hole wave scattering, establishing bounds from causality and discussing the potential for detection via gravitational wave observations.

Contribution

It provides new bounds on scalar-Gauss-Bonnet gravity theories and analyzes their detectability in gravitational wave signals from black hole mergers.

Findings

Lower bounds on theory cutoff scales from causality constraints

Scalar-Gauss-Bonnet couplings can produce hairy black holes

Enhanced detectability of scalar modes in gravitational wave observations

Abstract

We investigate time delays of wave scatterings around black hole backgrounds in scalar-tensor effective field theories of gravity. The scalar-Gauss-Bonnet (sGB) couplings, being corrections of the lowest orders, can give rise to hairy black holes. By requiring infrared causality, we impose lower bounds on the cutoff scales of the theories. With these bounds, we further discuss the detectability of sGB gravity in gravitational waves from binary black hole mergers. Compared with the gravitational effective field theories that contain only the two tensor modes, adding extra degrees of freedom, such as adding a scalar, opens up a detectable window in the planned observations.