Non-gaussianity of inflationary field perturbations from the field equation

TL;DR

This paper calculates the bispectrum of inflaton field perturbations directly from the field equations, confirming previous results and discussing the classical evolution of perturbations after horizon exit.

Contribution

It provides a direct calculation of the bispectrum from the field equations and clarifies the role of classical evolution in the quantum-to-classical transition.

Findings

Results agree with previous Lagrangian-based calculations.

Highlights the importance of classical evolution after horizon exit.

Supports using quantum theory only at the initial classicalization point.

Abstract

We calculate the tree-level bispectrum of the inflaton field perturbation directly from the field equations, and construct the corresponding f_NL parameter. Our results agree with previous ones derived from the Lagrangian. We argue that quantum theory should only be used to calculate the correlators when they first become classical a few Hubble times after horizon exit, the classical evolution taking over thereafter.