CMB constraint on non-Gaussianity in isocurvature perturbations

TL;DR

This paper constrains the non-Gaussianity of CDM isocurvature perturbations using WMAP 7-year CMB data, providing bounds that inform early Universe models like axion CDM scenarios.

Contribution

It presents the first constraints on non-Gaussianity in uncorrelated CDM isocurvature perturbations using advanced CMB analysis techniques.

Findings

Constraint on alpha^2 f_{NL}^{(ISO)}=40±66 assuming Gaussian adiabatic perturbations.

Constraint on f_{NL}=38±24 allowing non-Gaussian adiabatic perturbations.

Implications for axion CDM isocurvature models discussed.

Abstract

We study the CMB constraint on non-Gaussianity in CDM isocurvature perturbations. Non-Gaussian isocurvature perturbations can be produced in various models at the very early stage of the Universe. Since the isocurvature perturbations little affect the structure formation at late times, CMB is the best probe of isocurvature non-Gaussianity at least in the near future. In this paper, we focus on uncorrelated isocurvature perturbations and constrain their non-Gaussianity. For this purpose, we employ several state-of-art techniques for the analysis of CMB data and simulation. We use the WMAP 7 year data of temperature anisotropy. When the adiabatic perturbations are assumed to be Gaussian, we obtained a constraint on the isocurvature non-Gaussianity alpha^2 f_{NL}^{(ISO)}=40+-66 for the scale invariant isocurvature power spectrum, where alpha is the ratio of the power spectrum of isocurvature perturbations to that of the adiabatic ones. When we assume that the adiabatic perturbations can also be non-Gaussian, we obtain f_{NL}=38+-24 and alpha^2 f_{NL}^{(ISO)}=-8+-72. We also discuss implications our results for the axion CDM isocurvature model.