A quantum heating as an alternative of reheating

TL;DR

This paper investigates quantum effects in a scalar field during a cosmological expansion, showing that quantum loop corrections can induce thermalization after expansion, offering an alternative to traditional reheating models.

Contribution

It demonstrates that quantum loop corrections become significant during inflation, leading to particle excitation and thermalization, providing a novel perspective on reheating mechanisms.

Findings

Quantum loop corrections are non-negligible during inflation.

Expansion induces non-zero particle density in the scalar field.

Quantum effects lead to thermalization in the post-expansion stage.

Abstract

To model a realistic situation for the beginning we consider massive real scalar $\phi^4$ theory in a (1+1)-dimensional asymptotically static Minkowski spacetime with an intermediate stage of expansion. To have an analytic headway we assume that scalars have a big mass. At past and future infinities of the background we have flat Minkowski regions which are joint by the inflationary expansion region. We use the tree-level Keldysh propagator in the theory in question to calculate the expectation value of the stress-energy tensor which is, thus, due to the excitations of the zero-point fluctuations. Then we show that even for large mass, if the de Sitter expansion stage is long enough, the quantum loop corrections to the expectation value of the stress-energy tensor are not negligible in comparison with the tree-level contribution. That is revealed itself via the excitation of the higher-point fluctuations of the exact modes: During the expansion stage a non-zero particle number density for the exact modes is generated. This density is not Plankian and serves as a quench which leads to a thermalization in the out Minkowski stage.