Limits on Isocurvature Perturbations from Non-Gaussianity in WMAP Temperature Anisotropies

TL;DR

This paper investigates how primordial isocurvature perturbations influence non-Gaussian features in CMB temperature anisotropies, deriving analytical tools and applying them to WMAP data to constrain isocurvature contributions.

Contribution

It provides analytical expressions for the bispectrum and Minkowski Functionals related to isocurvature non-Gaussianity and applies these to observational data to set new limits.

Findings

No significant isocurvature non-Gaussianity detected

Upper limit on isocurvature fraction alpha<0.070 (95% CL)

Quadratic isocurvature model can mimic f_NL=30 signal-to-noise

Abstract

We study the effect of primordial isocurvature perturbations on non-Gaussian properties of CMB temperature anisotropies. We consider generic forms of the non-linearity of isocurvature perturbations which can be applied to a wide range of theoretical models. We derive analytical expressions for the bispectrum and the Minkowski Functionals for CMB temperature fluctuations to describe the non-Gaussianity from isocurvature perturbations. We find that the isocurvature non-Gaussianity in the quadratic isocurvature model, where the isocurvature perturbation S is written as a quadratic function of the Gaussian variable sigma, S=sigma^2-<sigma^2>, can give the same signal-to-noise as f_NL=30 even if we impose the current observational limit on the fraction of isocurvature perturbations contained in the primordial power spectrum alpha. We give constraints on isocurvature non-Gaussianity from Minkowski Functionals using WMAP 5-year data. We do not find a significant signal of the isocurvature non-Gaussianity. For the quadratic isocurvature model, we obtain a stringent upper limit on the isocurvature fraction alpha<0.070 (95% CL) for a scale invariant spectrum which is comparable to the limit obtained from the power spectrum.