Primordial non-Gaussianity from mixed inflaton-curvaton perturbations

TL;DR

This paper investigates how mixed inflaton and curvaton fluctuations can produce observable non-Gaussianity in the early universe, analyzing various potential forms and deriving constraints from observational data.

Contribution

It characterizes primordial perturbations from mixed inflaton-curvaton models with different potentials and derives new relations between non-Gaussianity parameters and observational constraints.

Findings

Curvaton fluctuations can produce significant non-Gaussianity unlike inflaton fluctuations.

A consistency relation between bispectrum and trispectrum parameters is established for quadratic curvaton potentials.

Self-interactions in the curvaton potential can enhance trispectrum signals and introduce scale dependence.

Abstract

We characterise the primordial perturbations produced due to both inflaton and curvaton fluctuations in models where the curvaton has a quadratic, cosine or hyperbolic potential, and the inflaton potential is characterised by the usual slow-roll parameters. Isocurvature curvaton field perturbations can produce significant non-Gaussianity in the primordial density field, in contrast with adiabatic inflaton field perturbations which produce negligible non-Gaussianity for canonical scalar fields. A non-self-interacting curvaton with quadratic potential produces a local-type non-Gaussianity that is well described by the non-linearity parameter fNL, which may be scale-dependent when the inflaton perturbations dominate the power spectrum. We show how observational bounds on non-linearity parameters and the tensor-scalar ratio can be used to constrain curvaton and inflaton parameters. We find a consistency relation between the bispectrum and trispectrum parameters in a mixed inflaton-curvaton model for a quadratic curvaton potential. Self-interaction terms in the curvaton potential can lead to both a large trispectrum parameter, gNL, and scale-dependence of the non-linearity parameters.