Primordial non-Gaussianity from two curvaton decays

TL;DR

This paper investigates a two-curvaton decay model where both fields influence primordial curvature perturbations, calculating the power spectrum and non-linearity parameter, fNL, revealing large non-Gaussianity under various decay scenarios.

Contribution

It provides a comprehensive analysis of non-Gaussianity from two curvatons, extending single-curvaton results to more complex decay interactions and their impact on primordial perturbations.

Findings

Large positive fNL when curvatons are sub-dominant at decay

Large fNL can occur even if curvatons dominate energy density

Minimum fNL value of -5/4 matches single-curvaton case

Abstract

We study a model where two scalar fields, that are subdominant during inflation, decay into radiation some time after inflation has ended but before primordial nucleosynthesis. Perturbations of these two curvaton fields can be responsible for the primordial curvature perturbation. We write down the full non-linear equations that relate the primordial perturbation to the curvaton perturbations on large scales, calculate the power spectrum of the primordial perturbation, and finally go to second order to find the non-linearity parameter, fNL. We find large positive values of fNL if the energy densities of the curvatons are sub-dominant when they decay, as in the single curvaton case. But we also find a large fNL even if the curvatons dominate the total energy density in the case when the inhomogeneous radiation produced by the first curvaton decay is diluted by the decay of a second nearly homogeneous curvaton. The minimum value min(fNL)=-5/4 which we find is the same as in the single-curvaton case.