More accurate slow-roll approximations for inflation in scalar-tensor theories

TL;DR

This paper introduces improved slow-roll approximation formulas for inflation in scalar-tensor theories, enhancing accuracy in predicting inflationary parameters like the tensor-to-scalar ratio and scalar perturbation amplitude.

Contribution

The authors develop more precise slow-roll expressions for nonminimally coupled scalar fields, validated through models including Higgs-driven inflation, improving estimation accuracy of inflationary observables.

Findings

Enhanced accuracy of slow-roll parameters at the end of inflation

More precise estimations of tensor-to-scalar ratio $r$

Better predictions for scalar perturbation amplitude $A_s"

Abstract

We propose new versions of the slow-roll approximation for inflationary models with nonminimally coupled scalar fields. We derive more precise expressions for the standard slow-roll parameters as functions of the scalar field. To verify the accuracy of the proposed approximations, we consider inflationary models with the induced gravity term and the fourth-order monomial potential. For specific values of the model parameters, this model is the well-known Higgs-driven inflationary model. We investigate the inflationary dynamics in the Jordan frame and come to the conclusion that the proposed versions of the slow-roll approximation are not only more accurate at the end of inflation, but also give essentially more precise estimations for the tensor-to-scalar ratio $r$ and the amplitude of scalar perturbations $A_s$.