Curvature Spectra and Nongaussianities in the Roulette Inflation Model

TL;DR

This paper investigates nongaussianities in the roulette inflation model using the gradient expansion method, finding that superhorizon isocurvature effects produce negligible non-Gaussianity compared to standard inflation predictions.

Contribution

It applies the gradient expansion approach to a two-field inflation model to analyze nongaussianities and quantifies their small magnitude relative to standard predictions.

Findings

Superhorizon isocurvature modes produce negligible f_NL.

Both squeezed and equilateral bispectrum configurations show minimal non-Gaussianity.

The effect is slightly larger in the squeezed configuration.

Abstract

Using the gradient expansion method of Rigopoulos, Shellard and van Tent which treats cosmological perturbations as gradients on top of a homogeneous and isotropic FRW background, we study the production of nongaussianities in the roulette model of inflation. Investigating a number of trajectories within this two-field model of inflation, we find that while the superhorizon influence of the isocurvature modes on the curvature bispectrum produces nonzero contribution to f_NL, the effect is negligible next to the standard inflationary prediction |f_NL| ~ n_s - 1. This is the case in both the squeezed and equilateral configurations of the bispectrum, although the former is slightly larger in the trajectories under consideration.