Review of local non-Gaussianity from multi-field inflation

TL;DR

This paper reviews various multi-field inflation models that produce significant local non-Gaussianity, analyzing conditions and formalisms for their generation during and after inflation, including non-slow-roll scenarios and additional observables.

Contribution

It provides a comprehensive review of models generating local non-Gaussianity, deriving conditions for potential functions, and introducing a formalism for non-slow-roll inflation scenarios.

Findings

Identified conditions for large local bispectrum during slow-roll inflation.

Developed a formalism applicable to models with large slow-roll parameters.

Analyzed scale dependence of f_NL and the trispectrum in multi-field inflation.

Abstract

We review models which generate a large non-Gaussianity of the local form. We first briefly consider three models which generate the non-Gaussianity either at or after the end of inflation; the curvaton scenario, modulated (p)reheating and an inhomogeneous end of inflation. We then focus on ways of generating the non-Gaussianity during inflation. We derive general conditions which a product or sum separable potential must satisfy in order to generate a large local bispectrum during slow-roll inflation. As an application we consider two-field hybrid inflation. We then derive a formalism not based on slow roll which can be applied to models in which the slow-roll parameters become large before inflation ends. An exactly soluble two-field model is given in which this happens. Finally we also consider further non-Gaussian observables; a scale dependence of f_NL and the trispectrum.