Non-Gaussianities in the Cosmological Perturbation Spectrum due to Primordial Anisotropy II

TL;DR

This paper explores how primordial anisotropy affects non-Gaussianities in the cosmological perturbation spectrum, revealing regimes with significant non-Gaussianity and others where it remains negligible, depending on momentum configurations.

Contribution

It provides a detailed analysis of non-Gaussian signatures arising from primordial anisotropy, especially highlighting the impact on planar modes and the limitations of linear perturbation theory.

Findings

Enhanced non-Gaussianity in certain squeezed configurations for planar modes.

Scale invariance of the power spectrum can be strongly broken in some regimes.

Non-Gaussianity remains extremely small when scale invariance is preserved.

Abstract

We continue to investigate possible signatures of a pre-inflationary anisotropic phase in two-point and three point correlation functions of the curvature perturbation for high-momentum modes which exit the horizon well after isotropization. The late time dynamics of these modes is characterized by a non-Bunch Davies vacuum state which encodes all the information about initial anisotropy in the background space-time. We observe that, unlike the non-planar momenta, there exist regimes of planar momenta for which scale invariance of the power spectrum is strongly broken. This regime of planar momenta gives rise to enhanced non-Gaussianity in certain squeezed triangle configurations, although the enhancement of the $f_{NL}$ parameter is limited by the breakdown of linear perturbation theory at "exact planarity". Finally, we demonstrate that for the range of planar modes for which scale invariance of the power spectrum is preserved, non-Gaussianity in the curvature perturbation spectrum is naturally constrained to be extremely small.