2017/09/30 by Yuichiro Nakai, Noburo Shiba, Masaki Yamada · 1 citation
Physics and Astronomy · #Black Holes and Theoretical Physics #Cosmology and Gravitation Theories #Decoupling (probability) #Entropy (arrow of time) #Entropy in thermodynamics and information theory #Entropy rate #Generalized relative entropy #Joint quantum entropy #Maximum entropy thermodynamics #Physics #Quantum #Quantum Electrodynamics and Casimir Effect #Quantum discord #Quantum entanglement #Quantum mechanics #Quantum relative entropy #Statistical physics #astro-ph.CO #hep-ph #hep-th
paper · pdf · doi:10.1103/physrevd.96.123518
published as Phys. Rev. D 96, 123518 (2017) · 32 pages, 8 figures; v2: published version
arxiv created 2017/12/11 · openalex publication_date 2017/12/15 · arxiv updated 2017/12/20 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
In the expanding universe, two interacting fields are no longer in thermal contact when the interaction rate becomes smaller than the Hubble expansion rate. After decoupling, two subsystems are usually treated separately in accordance with equilibrium thermodynamics and the thermodynamic entropy gives a fiducial quantity conserved in each subsystem. In this paper, we discuss a correction to this paradigm from quantum entanglement of two coupled fields. The thermodynamic entropy is generalized to the entanglement entropy. We formulate a perturbation theory to derive the entanglement entropy and present Feynman rules in diagrammatic calculations. For specific models to illustrate our formulation, an interacting scalar-scalar system, quantum electrodynamics, and the Yukawa theory are considered. We calculate the entanglement entropy in these models and find a quantum correction to the thermodynamic entropy. The correction is revealed to be important in circumstances of instantaneous decoupling.