\delta N versus covariant perturbative approach to non-Gaussianity outside the horizon in multifield inflation

TL;DR

This paper compares two formalisms for calculating non-Gaussianity in two-field inflation, showing they agree closely and analyzing how the non-Gaussianity parameter evolves as inflation progresses.

Contribution

It demonstrates the quantitative agreement between delta N and covariant formalisms for non-Gaussianity in multifield inflation and analytically describes the decay rate of f_{NL}.

Findings

delta N and covariant formalisms agree within 1%

f_{NL} decays no faster than a^{-3} near the adiabatic limit

Analytical expression for the decay of non-Gaussianity

Abstract

We compute the super-Hubble evolution of non-Gaussianity of primordial curvature perturbations in two-field inflation models by employing two formalisms: delta N and covariant formalisms. Although two formalisms treat the evolution of fluctuations radically different, we show that the formulas of f_{NL} parameter agree quantitatively with each other within 1 % accuracy. We analytically find that the amplitude of f_{NL} decays no faster than a^{-3} as the inflationary trajectory reaches to the adiabatic limit for generic potentials.