Second-order stochastic theory for self-interacting scalar fields in de Sitter spacetime

TL;DR

This paper develops a second-order stochastic effective theory for light scalar fields in de Sitter space, extending the stochastic approach's applicability to stronger self-interactions and providing a non-perturbative method for calculating long-distance correlations.

Contribution

It introduces a second-order stochastic framework for scalar fields in de Sitter space, valid for larger self-interactions, and connects it with quantum field theory through perturbative parameter determination.

Findings

The second-order stochastic theory matches quantum field theory results in applicable regimes.

It extends the validity of stochastic methods beyond the massless limit.

Potential for improved accuracy with full one-loop parameter calculations.

Abstract

We introduce a second-order stochastic effective theory for light scalar fields in de Sitter spacetime, extending the validity of the stochastic approach beyond the massless limit and demonstrating how it can be used to compute long-distance correlation functions non-perturbatively. The parameters of the second-order stochastic theory are determined from quantum field theory through a perturbative calculation, which is valid if the self-interaction parameter $\lambda$ satisfies $\lambda\ll m^2/H^2$, where $m$ is the scalar and $H$ is the Hubble rate. Therefore it allows stronger self-interactions than conventional perturbation theory, which is limited to $\lambda\ll m^4/H^4$ by infrared divergences. We demonstrate the applicability of the second-order stochastic theory by comparing its results with perturbative quantum field theory and overdamped stochastic calculations, and discuss the prospects of improving its accuracy with a full one-loop calculation of its parameters.