Quantum backreaction on a classical universe

TL;DR

This paper develops a numerical framework for the coupled evolution of a quantum scalar field and a classical universe, revealing how quantum backreaction influences cosmological dynamics and particle production.

Contribution

It introduces a self-consistent semiclassical model with a state-dependent Hamiltonian constraint and solves the non-linear equations numerically, including non-perturbative backreaction effects.

Findings

Backreaction modifies particle production rates.

Cosmological expansion is affected by quantum backreaction.

Effects of backreaction remain bounded over time.

Abstract

We study a first-order formulation for the coupled evolution of a quantum scalar field and a classical Friedmann universe. The model is defined by a state dependent hamiltonian constraint and the time dependent Schr\"odinger equation for the scalar field. We solve the resulting non-linear equations numerically for initial data consisting of a Gaussian scalar field state and gravity phase space variables. This gives a self-consistent semiclassical evolution that includes non-perturbative ``backreaction" due to particle production. We compare the results with the evolution of a quantum scalar field on a fixed background, and find that the backreaction modifies both particle production and cosmological expansion, and that these effects remain bounded.