On the Effective Field Theory for Quasi-Single Field Inflation

TL;DR

This paper develops an effective field theory framework for quasi-single field inflation, providing approximate formulas for key observables and demonstrating how these corrections can align inflation models with observational data, including non-Gaussianity predictions.

Contribution

It introduces a unified EFT approach for quasi-single field inflation, deriving accurate approximate expressions for the power spectrum and spectral index across parameter space.

Findings

Approximate expressions for power spectrum and spectral index with less than 10% error.

Quasi-single field corrections can bring $m^2\,\phi^2$ inflation into observationally favored regions.

Predictions include detectable equilateral non-Gaussianity in future experiments.

Abstract

We study the effective field theory (EFT) description of the virtual particle effects in quasi-single field inflation, which unifies the previous results on large mass and large mixing cases. By using a horizon crossing approximation and matching with known limits, approximate expressions for the power spectrum and the spectral index are obtained. The error of the approximate solution is within 10% in dominate parts of the parameter space, which corresponds to less-than-0.1% error in the $n_s$-$r$ diagram. The quasi-single field corrections on the $n_s$-$r$ diagram are plotted for a few inflation models. Especially, the quasi-single field correction drives $m^2\phi^2$ inflation to the best fit region on the $n_s$-$r$ diagram, with an amount of equilateral non-Gaussianity which can be tested in future experiments.