GW170817 viable Einstein–Gauss–Bonnet Higgs inflation confronted with ACT

In this work, we shall consider Higgs inflationary Einstein–Gauss–Bonnet theories that are compatible with the GW170817 event, which dictates that the gravitational wave speed of primordial tensor perturbations must satisfy the constraint [Formula: see text]. We consider Einstein–Gauss–Bonnet theories that yield directly [Formula: see text] for which theories, the scalar potential and the non-minimal Gauss–Bonnet scalar coupling function are related. We assume that the non-minimal Gauss–Bonnet scalar coupling function is identical with the Higgs potential, and we confront the resulting theory with the ACT data, to determine whether the theory is viable. As we show, the resulting theoretical framework is viable and compatible with the ACT data and the updated Planck constraints on the tensor-to-scalar ratio.