Why Must Primordial Non-Gaussianity Be Very Small?

TL;DR

This paper demonstrates that one-loop corrections in single-field inflation significantly constrain primordial non-Gaussianity, requiring it to be much smaller than current observational bounds to maintain the validity of perturbation theory.

Contribution

It calculates the one-loop correction to the power spectrum in single-field inflation, revealing the necessity for very small primordial non-Gaussianity.

Findings

One-loop corrections are larger than previously thought due to spectral tilt.

Primordial non-Gaussianity must be extremely small for perturbation theory validity.

Current observational bounds are not compatible with the theoretical constraints.

Abstract

One-loop correction to the power spectrum in generic single-field inflation is calculated by using standard perturbation theory. Because of the enhancement inversely proportional to the observed red tilt of the spectral index of curvature perturbation, the correction turns out to be much larger than previously anticipated. As a result, the primordial non-Gaussianity must be much smaller than the current observational bound in order to warrant the validity of cosmological perturbation theory.