Primordial gravitational waves predictions for GW170817-compatible Einstein–Gauss–Bonnet theory

Abstract

In this work we shall calculate in detail the effect of an GW170817-compatible Einstein–Gauss–Bonnet theory on the energy spectrum of the primordial gravitational waves. The spectrum is affected by two characteristics, the overall amplification/damping factor caused by the GW170817-compatible Einstein–Gauss–Bonnet theory and by the tensor spectral index and the tensor-to-scalar ratio. We shall present the formalism for studying the inflationary dynamics and post-inflationary dynamics of GW170817-compatible Einstein–Gauss–Bonnet theories for all redshifts starting from the radiation era up to the dark energy era. We exemplify our formalism by using two characteristic models, which produce viable inflationary and dark energy eras. As we demonstrate, remarkably the overall damping/amplification factor is of the order of unity, thus the GW170817-compatible Einstein–Gauss–Bonnet models affect the primordial gravitational waves energy spectrum only via their tensor spectral index and the tensor-to-scalar ratio. Both models have a blue tilted tensor spectrum, and therefore the predicted energy spectrum of the primordial gravity waves can be detectable by most of the future gravitational waves experiments, for various reheating temperatures.