Quantum fluctuations and semiclassicality in an inflaton-driven evolution

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 undergoes a large amount of squeezing that leads to considerable variance in the volume at its end; $(ii)$ 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 fluctuation effects (usually hoped to provide a source for a small cosmological constant) are washed out by the higher-order quantum corrections.