Non-linear isocurvature perturbations and non-Gaussianities

TL;DR

This paper investigates the non-linear aspects of primordial adiabatic and isocurvature perturbations, their non-Gaussianity, and provides detailed analysis of two inflationary models with potential for large isocurvature bispectra.

Contribution

It introduces a general extended delta N-formalism for non-linear perturbations and analyzes two specific inflationary scenarios with significant isocurvature non-Gaussianity.

Findings

Isocurvature bispectrum can be large and comparable to adiabatic bispectrum.

Provides a general formalism for non-linear primordial perturbations.

Analyzes mixed curvaton-inflaton and double inflation models.

Abstract

We study non-linear primordial adiabatic and isocurvature perturbations and their non-Gaussianity. After giving a general formulation in the context of an extended delta N-formalism, we analyse in detail two illustrative examples. The first is a mixed curvaton-inflaton scenario in which fluctuations of both the inflaton and a curvaton (a light isocurvature field during inflation) contribute to the primordial density perturbation. The second example is that of double inflation involving two decoupled massive scalar fields during inflation. In the mixed curvaton-inflaton scenario we find that the bispectrum of primordial isocurvature perturbations may be large and comparable to the bispectrum of adiabatic curvature perturbations.