Slow-roll inflation in $f(R,T)$ gravity with a $RT$ mixing term

TL;DR

This paper explores slow-roll inflation within a modified gravity framework that includes a novel $RT$ mixing term, revealing its significant impact on inflationary predictions and their alignment with observations.

Contribution

It introduces a new $RT$ mixing term in $f(R,T)$ gravity and demonstrates its influence on inflationary dynamics and observational compatibility.

Findings

The $RT$ mixing term affects spectral tilt and tensor-to-scalar ratio.

Including the $RT$ term improves agreement of chaotic and natural inflation with data.

The model shows sensitivity of inflationary predictions to the $RT$ coupling.

Abstract

We consider slow-roll inflationary models in a class of modified theories of gravity which contains non-minimal curvature-inflaton couplings, i.e., the $f(R,T)$ gravity, where $R$ is the Ricci scalar and $T$ is the trace of the inflaton energy-momentum tensor. On top of the minimally coupled $T$ that has been widely investigated in the literature, we further include a $RT$ mixing term in the theory. This mixing term introduces non-minimal derivative couplings and plays an important role in inflationary dynamics. Taking chaotic and natural inflation as examples, we find that the predictions for spectral tilt and the tensor-to-scalar ratio are sensitive to the existence of the $RT$ mixing term. In particular, by turning on this mixing term, it is possible to bring chaotic and natural inflation into better agreement with observational data.