Intrinsic Entropy of Squeezed Quantum Fields and Nonequilibrium Quantum Dynamics of Cosmological Perturbations

Density contrasts in the universe are governed by scalar cosmological perturbations which, when expressed in terms of gauge-invariant variables, contain a classical component from scalar metric perturbations and a quantum component from inflaton field fluctuations. It has long been known that the ef...

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Autores principales:	Jen-Tsung Hsiang, Bei-Lok Hu
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	cosmological particle creation entropy generation nonequilibrium field theory cosmological perturbations Science Q Astrophysics QB460-466 Physics QC1-999
Acceso en línea:	https://doaj.org/article/98801385e80f41d5a0a6d5b1a5570fe3
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spelling	oai:doaj.org-article:98801385e80f41d5a0a6d5b1a5570fe32021-11-25T17:30:52ZIntrinsic Entropy of Squeezed Quantum Fields and Nonequilibrium Quantum Dynamics of Cosmological Perturbations10.3390/e231115441099-4300https://doaj.org/article/98801385e80f41d5a0a6d5b1a5570fe32021-11-01T00:00:00Zhttps://www.mdpi.com/1099-4300/23/11/1544https://doaj.org/toc/1099-4300Density contrasts in the universe are governed by scalar cosmological perturbations which, when expressed in terms of gauge-invariant variables, contain a classical component from scalar metric perturbations and a quantum component from inflaton field fluctuations. It has long been known that the effect of cosmological expansion on a quantum field amounts to squeezing. Thus, the entropy of cosmological perturbations can be studied by treating them in the framework of squeezed quantum systems. Entropy of a free quantum field is a seemingly simple yet subtle issue. In this paper, different from previous treatments, we tackle this issue with a fully developed nonequilibrium quantum field theory formalism for such systems. We compute the covariance matrix elements of the parametric quantum field and solve for the evolution of the density matrix elements and the Wigner functions, and, from them, derive the von Neumann entropy. We then show explicitly why the entropy for the squeezed yet closed system is zero, but is proportional to the particle number produced upon coarse-graining out the correlation between the particle pairs. We also construct the bridge between our quantum field-theoretic results and those using the probability distribution of classical stochastic fields by earlier authors, preserving some important quantum properties, such as entanglement and coherence, of the quantum field.Jen-Tsung HsiangBei-Lok HuMDPI AGarticlecosmological particle creationentropy generationnonequilibrium field theorycosmological perturbationsScienceQAstrophysicsQB460-466PhysicsQC1-999ENEntropy, Vol 23, Iss 1544, p 1544 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	cosmological particle creation entropy generation nonequilibrium field theory cosmological perturbations Science Q Astrophysics QB460-466 Physics QC1-999
spellingShingle	cosmological particle creation entropy generation nonequilibrium field theory cosmological perturbations Science Q Astrophysics QB460-466 Physics QC1-999 Jen-Tsung Hsiang Bei-Lok Hu Intrinsic Entropy of Squeezed Quantum Fields and Nonequilibrium Quantum Dynamics of Cosmological Perturbations
description	Density contrasts in the universe are governed by scalar cosmological perturbations which, when expressed in terms of gauge-invariant variables, contain a classical component from scalar metric perturbations and a quantum component from inflaton field fluctuations. It has long been known that the effect of cosmological expansion on a quantum field amounts to squeezing. Thus, the entropy of cosmological perturbations can be studied by treating them in the framework of squeezed quantum systems. Entropy of a free quantum field is a seemingly simple yet subtle issue. In this paper, different from previous treatments, we tackle this issue with a fully developed nonequilibrium quantum field theory formalism for such systems. We compute the covariance matrix elements of the parametric quantum field and solve for the evolution of the density matrix elements and the Wigner functions, and, from them, derive the von Neumann entropy. We then show explicitly why the entropy for the squeezed yet closed system is zero, but is proportional to the particle number produced upon coarse-graining out the correlation between the particle pairs. We also construct the bridge between our quantum field-theoretic results and those using the probability distribution of classical stochastic fields by earlier authors, preserving some important quantum properties, such as entanglement and coherence, of the quantum field.
format	article
author	Jen-Tsung Hsiang Bei-Lok Hu
author_facet	Jen-Tsung Hsiang Bei-Lok Hu
author_sort	Jen-Tsung Hsiang
title	Intrinsic Entropy of Squeezed Quantum Fields and Nonequilibrium Quantum Dynamics of Cosmological Perturbations
title_short	Intrinsic Entropy of Squeezed Quantum Fields and Nonequilibrium Quantum Dynamics of Cosmological Perturbations
title_full	Intrinsic Entropy of Squeezed Quantum Fields and Nonequilibrium Quantum Dynamics of Cosmological Perturbations
title_fullStr	Intrinsic Entropy of Squeezed Quantum Fields and Nonequilibrium Quantum Dynamics of Cosmological Perturbations
title_full_unstemmed	Intrinsic Entropy of Squeezed Quantum Fields and Nonequilibrium Quantum Dynamics of Cosmological Perturbations
title_sort	intrinsic entropy of squeezed quantum fields and nonequilibrium quantum dynamics of cosmological perturbations
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/98801385e80f41d5a0a6d5b1a5570fe3
work_keys_str_mv	AT jentsunghsiang intrinsicentropyofsqueezedquantumfieldsandnonequilibriumquantumdynamicsofcosmologicalperturbations AT beilokhu intrinsicentropyofsqueezedquantumfieldsandnonequilibriumquantumdynamicsofcosmologicalperturbations
_version_	1718412239826845696

Intrinsic Entropy of Squeezed Quantum Fields and Nonequilibrium Quantum Dynamics of Cosmological Perturbations

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