Mild quasi-local non-Gaussianity as a signature of modified gravity during inflation

TL;DR

This paper explores how modifications to Einstein gravity during inflation, specifically in the form of an extra field, can produce measurable non-Gaussian signatures in cosmological observations, with potential implications for understanding gravity's role in early universe dynamics.

Contribution

It demonstrates that modified gravity models like $R+eta R^2$ can generate observable quasi-local non-Gaussianity during inflation, providing a new potential signature of such theories.

Findings

Nearly scale-invariant non-Gaussianity with $f_{NL} \, \approx \, -(1\text{ to }30)$ can arise.

Modified gravity introduces an extra field interacting with the inflaton, affecting cosmological perturbations.

The non-Gaussianity signature is quasi-local, distinguishable in cosmological data.

Abstract

We show that modifications of Einstein gravity during inflation could leave potentially measurable imprints on cosmological observables in the form of non-Gaussian perturbations. This is due to the fact that these modifications appear in the form of an extra field that could have non-trivial interactions with the inflaton. We show it explicitly for the case $R+\alpha R^2$, where nearly scale-invariant non-Gaussianity at the level of $f_{\rm NL} \approx -(1$ to $30)$ can be obtained, in a quasi-local configuration.