Inflationary predictions at small gamma

TL;DR

This paper investigates single field inflation models with a constant speed of sound c_s, analyzing how inflationary observables depend on c_s, and finds that this dependence is generally weak within current non-gaussianity constraints.

Contribution

It introduces a simple parameterization of non-gaussianity through a constant c_s in Dirac-Born-Infeld inflation models and examines its effect on inflationary predictions.

Findings

Dependence of observables on c_s is weak within current bounds

Non-gaussianity can be parameterized by c_s in these models

Most inflationary predictions are robust against variations in c_s

Abstract

This paper explores single field inflation models with a constant, but arbitrary speed of sound c_s, obtained by deforming the kinetic energy terms to a Dirac-Born-Infeld form. Allowing c_s<1 provides a simple parameterization of non-gaussianity. The dependence of inflationary observables on the parameter c_s is considered in the leading order slow roll approximation. The results show that in most cases the dependence is actually rather weak for the range of c_s allowed by existing bounds on non-gaussianity.