Primordial Trispectrum from Isocurvature Fluctuations

TL;DR

This paper develops a general formalism to analyze non-Gaussianities from adiabatic and isocurvature primordial perturbations, applying it to mixed curvaton-inflaton models with multiple decay channels, revealing potential for significant non-Gaussian signals.

Contribution

It introduces a comprehensive third-order perturbation framework for multiple fluids and decay processes, and applies it to mixed curvaton-inflaton models to explore non-Gaussianity.

Findings

Significant non-Gaussianity can arise from isocurvature perturbations.

Isocurvature non-Gaussianity can dominate over adiabatic in certain scenarios.

Non-Gaussian signals are compatible with current isocurvature constraints.

Abstract

We study non-Gaussianity generated by adiabatic and isocurvature primordial perturbations. We first obtain, in a very general setting, the non-linear perturbations, up to third order, for an arbitrary number of cosmological fluids, going through one or several decay transitions. We then apply this formalism to the mixed curvaton and inflaton model, allowing for several decay channels. We compute the various contributions to the bispectrum and trispectrum resulting from adiabatic and isocurvature perturbations, which are correlated in general. By investigating some hybrid decay scenario, we show that significant non-Gaussianity of adiabatic and isocurvature types can be generated without conflicting with the present isocurvature constraints from the power spectrum. In particular, we find cases where non-Gaussianity of isocurvature origin can dominate its adiabatic counterpart, both in the bispectrum and in the trispectrum.