Squeezed primordial bispectrum from general vacuum state

TL;DR

This paper derives a general formula linking the power spectrum and the squeezed bispectrum in single-field inflation with a general vacuum, revealing conditions for scale-invariant non-Gaussianity.

Contribution

It provides a new, non-slow-roll suppressed expression for the squeezed bispectrum parameter fNL in terms of a free parameter, expanding understanding of initial states in inflation.

Findings

Derived a formula for the squeezed bispectrum with a general vacuum.

Identified conditions for scale-invariant fNL.

Discussed examples illustrating the theoretical framework.

Abstract

We study the general relation between the power spectrum and the squeezed limit of the bispectrum of the comoving curvature perturbation produced during single-field slow-roll inflation when the initial state is a general vacuum. Assuming the scale invariance of the power spectrum, we derive a formula for the squeezed limit of the bispectrum, represented by the parameter fNL, which is not slow-roll suppressed and is found to contain a single free parameter for a given amplitude of the power spectrum. Then we derive the conditions for achieving a scale-invariant fNL, and discuss a few examples.