Decoherence Functional and Inhomogeneities in the Early Universe

TL;DR

This paper explores how quantum fluctuations in the early Universe become classical, comparing two different coarse-graining methods using the decoherence functional, and highlighting their differing outcomes.

Contribution

It introduces a comparison of two coarse-graining approaches in the context of quantum decoherence in cosmology, revealing their differences.

Findings

Different results from the two coarse-graining methods

Comparison with Zurek's off-diagonal rule

Insights into quantum-classical transition in the early Universe

Abstract

We investigate the quantum to classical transition of small inhomogeneous fluctuations in the early Universe using the decoherence functional of Gell-Mann and Hartle. We study two types of coarse graining; one due to coarse graining the value of the scalar field and the other due to summing over an environment. We compare the results with a previous study using an environment and the off-diagonal rule proposed by Zurek. We show that the two methods give different results.