Natural inflation in Palatini F(R,X)

Abstract

In the context of Palatini gravity, F(R+X) models, with X the inflaton kinetic term, are characterized by the appealing property of generating asymptotically flat inflaton potentials, exactly like the more commonly studied Palatini F(R) models, but without the complication of non-canonical inflaton kinetic terms in the Einstein frame. In this paper, we study the case of a Jordan frame potential which is positive and bounded, specifically, natural inflation. We compute the CMB observables and show that for a wide class of F(R + X) theories, including the quadratic one, natural inflation is still viable.