A General Analysis of Non-Gaussianity from Isocurvature Perturbations

TL;DR

This paper develops a comprehensive method to analyze non-Gaussianity and isocurvature perturbations in the cosmic microwave background, highlighting their distinct signatures on the bispectrum and exploring various explicit models.

Contribution

It introduces a general framework for calculating non-Gaussianity in adiabatic and isocurvature perturbations, including correlated cases, with applications to specific examples.

Findings

Distinct bispectrum signatures for non-Gaussianity and isocurvature perturbations

Method applicable to multiple explicit models

Enhanced understanding of correlations in CMB fluctuations

Abstract

Light scalars may be ubiquitous in nature, and their quantum fluctuations can produce large non-Gaussianity in the cosmic microwave background temperature anisotropy. The non-Gaussianity may be accompanied with a small admixture of isocurvature perturbations, which often have correlations with the curvature perturbations. We present a general method to calculate the non-Gaussianity in the adiabatic and isocurvature perturbations with and without correlations, and see how it works in several explicit examples. We also show that they leave distinct signatures on the bispectrum of the cosmic microwave background temperature fluctuations.