Non-Gaussianities in Multifield Inflation: Superhorizon Evolution, Adiabaticity, and the Fate of fnl

TL;DR

This paper investigates how large local non-Gaussianities can be generated during multifield inflation but tend to decay as the universe evolves towards an adiabatic state, highlighting the transient nature of such non-Gaussian signals.

Contribution

It provides an analytic framework using the delta N formalism to study the evolution and damping of non-Gaussianities in two-field inflation models.

Findings

Large fnl can be generated during inflation.

Non-Gaussianities are exponentially damped as fluctuations become adiabatic.

The evolution towards adiabaticity suppresses observable non-Gaussian signals.

Abstract

We explore the superhorizon generation of large fnl of the local form in two field inflation. We calculate the two- and three-point observables in a general class of potentials which allow for an analytic treatment using the delta N formalism. Motivated by the conservation of the curvature perturbation outside the horizon in the adiabatic mode and also by the observed adiabaticity of the power spectrum, we follow the evolution of fnl^{local} until it is driven into the adibatic solution by passing through a phase of effectively single field inflation. We find that although large fnl^{local} may be generated during inflation, such non-gaussianities are transitory and will be exponentially damped as the cosmological fluctuations approach adiabaticity.