Single-field inflation in models with an $R^2$ term

TL;DR

This paper shows that adding an $R^2$ term to certain inflation models simplifies them to single-field inflation and reduces the tensor-to-scalar ratio, which has implications for observational predictions.

Contribution

It demonstrates two specific cases where an $R^2$ term converts multi-field inflation into single-field inflation, a novel insight into inflationary model modifications.

Findings

Addition of $R^2$ term leads to single-field inflation

Reduces the tensor-to-scalar ratio $r$ in the models

Provides new pathways for inflation model simplification

Abstract

We present two cases where the addition of the $R^2$ term to an inflationary model leads to single-field inflation instead of two-field inflation as is usually the case. In both cases we find that the effect of the $R^2$ term is to reduce the value of the tensor-to-scalar ratio $r$.