Gravity and non-gravity mediated couplings in multiple-field inflation

TL;DR

This paper reviews mechanisms for generating primordial non-Gaussian fluctuations in multiple-field inflation, highlighting how gravity and non-gravity mediated couplings can produce varying levels of non-Gaussianity, with potential for large effects in isocurvature directions.

Contribution

It extends single-field inflation results to multiple fields, analyzing gravity and non-gravity mediated couplings and their impact on non-Gaussianities, supported by a high-energy physics case study.

Findings

Gravity mediated couplings are common but modest.

Non-gravity mediated couplings can induce large non-Gaussianities.

Model predictions remain robust in specific high-energy physics scenarios.

Abstract

Mechanisms for the generation of primordial non-Gaussian metric fluctuations in the context of multiple-field inflation are reviewed. As long as kinetic terms remain canonical, it appears that nonlinear couplings inducing non-gaussianities can be split into two types. The extension of the one-field results to multiple degrees of freedom leads to gravity mediated couplings that are ubiquitous but generally modest. Multiple-field inflation offers however the possibility of generating non-gravity mediated coupling in isocurvature directions that can eventually induce large non-Gaussianities in the metric fluctuations. The robustness of the predictions of such models is eventually examined in view of a case study derived from a high-energy physics construction.