Modified gravity models for inflation: In conformity with observations

TL;DR

This paper introduces a modified gravity model with an $f()T$ term to improve inflationary predictions, aligning models like chaotic, natural, and Starobinsky inflation more closely with observational data.

Contribution

The paper proposes a new $f()T$ gravity framework for inflation, analyzing its effects on inflation dynamics and observational predictions, enhancing compatibility with data.

Findings

Improves agreement of chaotic and natural inflation with observations.

Allows larger tensor-to-scalar ratio in Starobinsky model.

Spectral tilt and tensor-to-scalar ratio are sensitive to the $f()T$ term.

Abstract

We consider a modified gravity framework for inflation by adding to the Einstein-Hilbert action a direct $f(\phi)T$ term, where $\phi$ is identified as the inflaton and $T$ is the trace of the energy-momentum tensor. The framework goes to Einstein gravity naturally when the inflaton decays out. We investigate inflation dynamics in this $f(\phi)T$ gravity (not to be confused with torsion-scalar coupled theories) on a general basis and then apply it to three well-motivated inflationary models. We find that the predictions for the spectral tilt and the tensor-to-scalar ratio are sensitive to this new $f(\phi)T$ term. This $f(\phi)T$ gravity brings chaotic and natural inflation into better agreement with data and allows a larger tensor-to-scalar ratio in the Starobinsky model.