Evolution of quantum field, particle content and classicality in the three stage universe

TL;DR

This paper investigates the evolution of a quantum scalar field through three cosmological stages, analyzing particle content and quantum-to-classical transition using analytical and numerical methods.

Contribution

It provides a detailed analysis of quantum field evolution across multiple universe phases, introducing a classicality parameter to track quantum-to-classical transition.

Findings

Particle content varies with universe stages

Quantum-to-classical transition characterized by a classicality parameter

Analytical and numerical results elucidate field evolution and particle creation

Abstract

We study the evolution of a quantum scalar field in a toy universe which has three stages of evolution, viz., (i) an early (inflationary) de Sitter phase (ii) radiation dominated phase and (iii) late-time (cosmological constant dominated) de Sitter phase. Using Schr\"odinger picture, the scalar field equations are solved separately for the three stages and matched at the transition points. The boundary conditions are chosen so that field modes in the early de Sitter evolves from Bunch-Davies vacuum state. We determine the (time-dependent) particle content of this quantum state for the entire evolution of the universe and describe the various features both numerically and analytically. We also describe the quantum to classical transition in terms of a {\it classicality parameter} which tracks the particle creation and its effect on phase space correlation of the quantum field.