Large Non-Gaussianity in Slow-Roll Inflation

TL;DR

This paper introduces a slow-roll inflation model where scalar perturbations have a reduced speed of sound, resulting in significant equilateral non-Gaussianity, and is protected by galileon symmetry, offering an alternative to DBI inflation.

Contribution

The paper proposes a novel slow-roll inflation scenario with subluminal scalar perturbations and large non-Gaussianity, protected by galileon symmetry, distinct from traditional models.

Findings

Scalar perturbations propagate at subluminal speeds.

Large equilateral non-Gaussianity proportional to 1/c_s^4.

Model is stable against large quantum corrections.

Abstract

Canonical models of single-field, slow-roll inflation do not lead to appreciable non-Gaussianity, unless derivative interactions of the inflaton become uncontrollably large. We propose a novel slow-roll scenario where scalar perturbations propagate at a subluminal speed, leading to sizeable equilateral non-Gaussianity, $f^{\rm equil}_{\rm NL}\propto 1/c_s^4$, largely insensitive to the ultraviolet physics. The model is based on a low-energy effective theory characterized by weakly broken invariance under internal galileon transformations, $\phi\to\phi+b_\mu x^\mu$, which protects the properties of perturbations from large quantum corrections. This provides the unique alternative to models such as DBI inflation in generating strongly subluminal/non-Gaussian scalar perturbations.