Stochastic Dynamics of Coarse-Grained Quantum Fields in Inflationary Universe

TL;DR

This paper demonstrates how coarse-graining quantum fields during inflation results in a classical stochastic description, with the quantum state becoming a squeezed coherent state that exhibits a random walk behavior.

Contribution

It introduces a framework connecting quantum field coarse-graining in de Sitter space to emergent classical stochastic dynamics, highlighting the nature of the quantum state as a squeezed coherent state.

Findings

Quantum coarse-graining leads to classical stochastic behavior.

The quantum state is a highly squeezed coherent state.

The scalar field's center performs a random walk on classical trajectories.

Abstract

It is shown how coarse-graining of quantum field ^M theory in de Sitter space leads to the emergence of a classical ^M stochastic description as an effective theory in the infra-red regime. ^M The quantum state of the coarse-grained scalar field is found to be a highly^M squeezed coherent state, whose center performs a random walk on a^M bundle of classical trajectories.^M