Stochastic wave equation with thermal noise in an expanding universe

TL;DR

This paper investigates the Einstein-Klein-Gordon system with thermal noise in an expanding universe, analyzing how quantum and thermal fluctuations of scalar fields depend on their interactions during inflation.

Contribution

It introduces a model incorporating thermal noise into the Einstein-Klein-Gordon system and examines the resulting fluctuations in an expanding universe context.

Findings

Fluctuations include both quantum and thermal components.

Fluctuation behavior depends on inflaton-environment interactions.

Thermal noise influences scalar field perturbations during inflation.

Abstract

We discuss Einstein-Klein-Gordon system in an environment of an infinite number of scalar fields leading to an external thermal noise. In the lowest order of metric and field perturbations the quadratic fluctuations consist of a sum of quantum and thermal fluctuations. We show that these fluctuations depend on the form of the interaction of the inflaton with the environment.