Stochastic approach to inflation II: classicality, coarse-graining and noises

TL;DR

This paper extends a semiclassical stochastic inflation framework to include general momentum distributions and smooth cutoffs, revealing how mode weighting affects classicality and noise characteristics in inflationary dynamics.

Contribution

It introduces a generalized approach to stochastic inflation with non-trivial momentum distributions and smooth cutoffs, analyzing their impact on classicality and noise properties.

Findings

Colored noises depend on cutoff choices.

Mode weighting influences effective classical dynamics.

Smooth cutoffs mitigate singular noise correlations.

Abstract

In this work we generalize a previously developed semiclassical approach to inflation, devoted to the analysis of the effective dynamics of coarse-grained fields, which are essential to the stochastic approach to inflation. We consider general non-trivial momentum distributions when defining these fields. The use of smooth cutoffs in momentum space avoids highly singular quantum noise correlations and allows us to consider the whole quantum noise sector when analyzing the conditions for the validity of an effective classical dynamical description of the coarse-grained field. We show that the weighting of modes has physical consequences, and thus cannot be considered as a mere mathematical artifact. In particular we discuss the exponential inflationary scenario and show that colored noises appear with cutoff dependent amplitudes.