Decoherence in quantum cosmology at the onset of inflation

TL;DR

This paper investigates how quantum fields influence the transition of the universe to classical behavior at the start of inflation, revealing new contributions to decoherence from Euclidean effective actions.

Contribution

It introduces a novel calculation of the inflaton's reduced density matrix including Euclidean effective actions and addresses regularisation issues in decoherence analysis.

Findings

Bosonic fields induce classical properties in the universe near inflation onset

Euclidean effective action contributes a new term to the density matrix

Dimensional regularisation violates density matrix consistency conditions

Abstract

We calculate the reduced density matrix for the inflaton field in a model of chaotic inflation by tracing out degrees of freedom corresponding to various bosonic fields. We find a qualitatively new contribution to the density matrix given by the Euclidean effective action of quantum fields. We regularise the ultraviolet divergences in the decoherence factor. Dimensional regularisation is shown to violate the consistency conditions for a density matrix as a bounded operator. A physically motivated conformal redefinition of the environmental fields leads to well-defined expressions. They show that due to bosonic fields the Universe acquires classical properties near the onset of inflation.