The Coherent State Representation of Quantum Fluctuations in the Early Universe

TL;DR

This paper develops a coherent state framework for quantum fluctuations in the early universe, offering an alternative to the Wigner function and exploring decoherence and entropy in this context.

Contribution

It introduces a coherent state representation for quantum fluctuations in an expanding universe, analyzing decoherence, entropy, and the impact of surface terms on scale invariance.

Findings

Coherent state representation is a useful alternative to the Wigner function.

Decoherence naturally explains the quantum to classical transition of fluctuations.

Scale invariant spectra depend on specific surface term choices.

Abstract

Using the squeezed state formalism the coherent state representation of quantum fluctuations in an expanding universe is derived. It is shown that this provides a useful alternative to the Wigner function as a phase space representation of quantum fluctuations. The quantum to classical transition of fluctuations is naturally implemented by decohering the density matrix in this representation. The entropy of the decohered vacua is derived. It is shown that the decoherence process breaks the physical equivalence between vacua that differ by a coordinate dependent phase generated by a surface term in the Lagrangian. In particular, scale invariant power spectra are only obtained for a special choice of surface term.