Speaker
Description
Scalar Gauss–Bonnet gravity is a promising class of extensions of General Relativity (GR), providing a simple test-bed for possible deviations in the gravitational wave signals from coalescing binary black holes (BHs). These theories are characterized by a scalar field non-minimally coupled to the Gauss–Bonnet invariant through a coupling function, and naturally encounter a breakdown of the effective description when the BH radius becomes comparable to, or smaller than, the characteristic length-scale of the GR correction. This breakdown manifests itself either as the existence of a minimum BH mass or as a loss of hyperbolicity of the perturbed field equations. We investigate how different choices of the coupling function affect the hyperbolicity properties of the theory and the resulting observable quantities, such as the scalar charge.