Equilateral Non-Gaussianity and New Physics on the Horizon

TL;DR

This paper explores how small sound speed in single-field inflation leads to large non-Gaussianities and discusses the potential influence of new physics near the Hubble scale on inflationary predictions.

Contribution

It introduces weakly-coupled completions of the effective theory of inflation to analyze the impact of new physics on observable non-Gaussianities.

Findings

Large non-Gaussianities arise with small sound speed.

New physics near the Hubble scale can modify inflationary predictions.

Constructed models show potential observational signatures of new physics.

Abstract

We examine the effective theory of single-field inflation in the limit where the scalar perturbations propagate with a small speed of sound. In this case the non-linearly realized time-translation symmetry of the Lagrangian implies large interactions, giving rise to primordial non-Gaussianities. When the non-Gaussianities are measurable, these interactions will become strongly coupled unless new physics appears close to the Hubble scale. Due to its proximity to the Hubble scale, the new physics is not necessarily decoupled from inflationary observables and can potentially affect the predictions of the model. To understand the types of corrections that may arise, we construct weakly-coupled completions of the theory and study their observational signatures.