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

We investigate time delays of gravitational wave and scalar wave scatterings around black hole backgrounds in scalar-Gauss-Bonnet effective field theories of gravity. By requiring infrared causality, we impose a lower bound on the cutoff scale of the theories. With this bound, we further discuss the detectability of scalar-Gauss-Bonnet gravity in gravitational waves from binary black hole mergers. Comparing with the gravitational effective field theories that only contain the two tensor modes, adding a scalar degree of freedom opens up a detectable window in the planned observations.