Non-Gaussianity from massless preheating

TL;DR

This paper investigates how massless preheating after inflation can generate observable non-Gaussian density perturbations, using lattice simulations and analytical approximations to predict the nonlinearity parameter fNL and constrain model parameters.

Contribution

It introduces a detailed methodology combining lattice simulations and the separate universes approximation to calculate non-Gaussianity from preheating, and applies it to constrain the massless preheating model.

Findings

Certain parameter values are ruled out due to excessive non-Gaussianity.

The analytical approximation scheme reproduces simulation results effectively.

Preheating can produce observable non-Gaussian density perturbations.

Abstract

Preheating can convert superhorizon fluctuations of light scalar fields present at the end of inflation into observable density perturbations. We show in detail how lattice field theory simulations and the separate universes approximation can be used to calculate these perturbations and make predictions for the nonlinearity parameter fNL . We also present a simple approximation scheme that can reproduce these results analytically. Applying these methods to the massless preheating model, we determine the parameter values that are ruled out by too high levels of non-Gaussianity.