Separable and non-separable multi-field inflation and large non-Gaussianity

TL;DR

This paper develops a $ abla$ formalism-based framework to analyze cosmological observables in multi-field inflation, revealing conditions for large non-Gaussianity during phase transitions ending inflation.

Contribution

It introduces a novel approach to compute observables for non-separable potentials and boundary conditions, focusing on curvature and isocurvature perturbations instead of traditional adiabatic and entropy modes.

Findings

Large non-Gaussianity parameters ($f_{NL} \\sim 80$, $\\tau_{NL} \\sim 20000$) can be generated in multi-field inflation.

Analytical and numerical solutions for cosmological observables are provided for complex potentials.

The framework applies to both separable and non-separable inflationary models.

Abstract

In this paper we provide a general framework based on $\delta N$ formalism to estimate the cosmological observables pertaining to the cosmic microwave background radiation for non-separable potentials, and for generic \emph{end of inflation} boundary conditions. We provide analytical and numerical solutions to the relevant observables by decomposing the cosmological perturbations along the curvature and the isocurvature directions, \emph{instead of adiabatic and entropy directions}. We then study under what conditions large bi-spectrum and tri-spectrum can be generated through phase transition which ends inflation. In an illustrative example, we show that large $f_{NL}\sim {\cal O}(80)$ and $\tau_{NL}\sim {\cal O}(20000)$ can be obtained for the case of separable and non-separable inflationary potentials.