Large field polynomial inflation in Palatini f (R, φ ) gravity

In this paper, we employ the Palatini formalism to investigate the dynamics of large-field inflation using a renormalizable polynomial inflaton potential in the context of f(R, q5) gravity. Assuming instant reheating, we make a comparative analysis of large-field polynomial inflation (PI). We first consider the minimal and non-minimal coupling of inflaton in R gravity, and then we continue with the minimally and non-minimally coupled inflaton in f(R, q5) gravity. We scan the parameter space for the inflationary predictions (ns and r ) consistent with the Planck and BICEP/Keck 2018 results as well as the sensitivity forecast of the future CMB-S4 and depict the compliant regions in the q5 0 - beta plane where q5 0 and beta are two parameters of polynomial inflation model which control the saddle point of the potential and the flatness in the vicinity of this point respectively. We find that a substantial portion of the parameter space aligns with the observational data.