Inflation in $f(R,T)$ Gravity

TL;DR

This paper models inflation within the $f(R,T)$ gravity framework, showing that the trace of the energy-momentum tensor influences inflation and can produce observables consistent with current data, extending beyond traditional GR models.

Contribution

It introduces the first inflationary scenarios in $f(R,T)$ gravity, analyzing geometric and scalar field driven inflation, highlighting the role of $T$ in inflationary dynamics.

Findings

Inflation observables are independent of e-foldings in geometric models.

Spectral index aligns with Planck 2018 data, scalar-to-tensor ratio is slightly higher.

Scalar field models with Klein-Gordon potential produce consistent inflationary predictions.

Abstract

The article presents modeling of inflationary scenarios for the first time in the $f(R,T)$ theory of gravity. We assume the $f(R,T)$ functional from to be $R + \eta T$, where $R$ denotes the Ricci scalar, $T$ the trace of the energy-momentum tensor and $\eta$ the model parameter (constant). We first investigated an inflationary scenario where the inflation is driven purely due to geometric effects outside of GR. We found the inflation observables to be independent of the number of e-foldings in this setup. The computed value of the spectral index is consistent with latest Planck 2018 dataset while the scalar to tensor ratio is a bit higher. We then proceeded to analyze the behavior of an inflation driven by $f(R,T)$ gravity coupled with a real scalar field. By taking the slow-roll approximation, we generated interesting scenarios where a Klein Gordon potential leads to observationally consistent inflation observables. Our results makes it clear-cut that in addition to the Ricci scalar and scalar fields, the trace of energy momentum tensor also play a major role in driving inflationary scenarios.