Slow-roll inflation in (R+R*4) gravity

TL;DR

This paper explores slow-roll inflation within an R+R*4 gravity model, demonstrating its potential for inflation but highlighting issues with the spectral index due to the eta-problem.

Contribution

It provides a detailed analysis of topological inflation in R*4-modified gravity and identifies the eta-problem affecting spectral index predictions.

Findings

Confirmed slow-roll inflation with exit in the model

Identified eta-problem causing unacceptable spectral index values

Demonstrated equivalence to scalar-tensor gravity for potential computation

Abstract

We reconsider the toy-model of topological inflation, based on the R*4-modified gravity. By using its equivalence to the certain scalar-tensor gravity model in four space-time dimensions, we compute the inflaton scalar potential and investigate a possibility of inflation. We confirm the existence of the slow-roll inflation with an exit. However, the model suffers from the eta-problem that gives rise to the unacceptable value of the spectral index n_s of scalar perturbations.