Hunting for Isocurvature Modes in the CMB non-Gaussianities

TL;DR

This paper explores new non-Gaussian shapes in the CMB caused by primordial isocurvature modes, proposing models that could produce detectable signals within current observational bounds.

Contribution

It introduces a comprehensive analysis of six distinct bispectrum shapes involving isocurvature modes and discusses their detectability with Planck.

Findings

Detection of non-Gaussian signals from isocurvature modes is possible within current bounds.

A class of early Universe models can produce various hierarchies of these bispectrum components.

Planck satellite has the potential to detect these new non-Gaussian shapes.

Abstract

We investigate new shapes of local primordial non-Gaussianities in the CMB. Allowing for a primordial isocurvature mode along with the main adiabatic one, the angular bispectrum is in general a superposition of six distinct shapes: the usual adiabatic term, a purely isocurvature component and four additional components that arise from correlations between the adiabatic and isocurvature modes. We present a class of early Universe models in which various hierarchies between these six components can be obtained, while satisfying the present upper bound on the isocurvature fraction in the power spectrum. Remarkably, even with this constraint, detectable non-Gaussianity could be produced by isocurvature modes. We finally discuss the prospects of detecting these new shapes with the Planck satellite.