Quantum fluctuations and semiclassicality in an inflaton-driven evolution

TL;DR

This paper investigates quantum effects in an inflationary universe model, revealing that semiclassical methods remain accurate despite rapid volume spreading during inflation, and higher-order quantum corrections diminish quantum variances post-inflation.

Contribution

It provides a detailed analysis of quantum fluctuations in an inflaton-driven universe, showing the robustness of semiclassical descriptions and the diminishing impact of quantum variances with higher-order corrections.

Findings

Rapid volume spreading during inflation increases quantum variance.

Semiclassical methods accurately describe quantum evolution during inflation.

Higher-order quantum corrections reduce quantum variances post-inflation.

Abstract

A semiclassical description of quantum systems is applied to probe the dynamics of the cosmological model of an inflationary universe with quadratic inflaton potential, described in a quantum framework of geometrodynamics. The systematic analysis, focusing in particular on the inflationary and post-inflationary epochs, revealed several surprising and counterintuitive features: $(i)$ during inflation the universe rapidly spreads out in volume which leads to significant relative variance by the end of inflation; $(ii)$ despite that, the quantum evolution can still be described to high accuracy by semiclassical methods; $(iii)$ moreover, in the post-inflationary epoch, as the order of included quantum corrections increases, the quantum trajectory approaches the classical one and the description involving second-order corrections only is actually the least accurate there. The consequence of the latter is that the effects of the quantum variances are washed out by the higher-order quantum corrections.