Inflation with Gauss-Bonnet correction: beyond slow-roll

Abstract: If a coupling between the inflaton and the Gauss-Bonnet term is introduced, many models of inflation that were ruled out by the most recent Planck data can be made viable again. The predictions for the scalar spectral index and tensor-to-scalar ratio are typically computed using the slow-roll approximation. In this paper we instead study the full equations of motion and determine the necessary initial conditions for reasonable inflation epoch. We derive the conditions under which the Friedmann equation admits positive solutions for the Hubble parameter. Then we study the possibility of the inflaton becoming trapped in a local potential minimum induced by the Gauss-Bonnet term. Finally we demonstrate the results on monomial potential models with a quadratic and a quartic potential and show that the slow-roll approximation becomes imprecise in the quartic case.