Entropy in quantum chromodynamics

TL;DR

This paper reviews various forms of zero-temperature entropy in QCD, including condensate disorder, soliton-induced vacuum entropy, entanglement entropy, and flux tube configurational entropy, highlighting their roles in confinement and chiral symmetry breaking.

Contribution

It provides a comprehensive overview of entropy manifestations in QCD and discusses their significance in understanding confinement and chiral symmetry breaking mechanisms.

Findings

Entanglement entropy scales with surface area, not volume.

Flux tube configurational entropy is key to confinement and chiral symmetry breaking.

Vacuum entropy from solitons contributes to confinement phenomena.

Abstract

We review the role of zero-temperature entropy in several closely-related contexts in QCD. The first is entropy associated with disordered condensates, including $< G_{\mu\nu}^2>$. The second is vacuum entropy arising from QCD solitons such as center vortices, yielding confinement and chiral symmetry breaking. The third is entanglement entropy, which is entropy associated with a pure state, such as the QCD vacuum, when the state is partially unobserved and unknown. Typically, entanglement entropy of an unobserved three-volume scales not with the volume but with the area of its bounding surface. The fourth manifestation of entropy in QCD is the configurational entropy of light-particle world-lines and flux tubes; we argue that this entropy is critical for understanding how confinement produces chiral symmetry breakdown, as manifested by a dynamically-massive quark, a massless pion, and a $< \bar{q}q>$ condensate.