Chiral Phase Transition in QCD and Vector Manifestation

TL;DR

This paper develops a theory using hidden local symmetry to describe the chiral phase transition in hot QCD matter, predicting vector manifestation where vector mesons become massless and degenerate with pions at the critical temperature.

Contribution

It introduces the vector manifestation scenario within the hidden local symmetry framework, providing new predictions for chiral symmetry restoration in hot QCD environments.

Findings

Vector charge susceptibility equals axial-vector susceptibility at T_c

Violation of vector dominance near T_c

Pion velocity approaches the speed of light

Abstract

Spontaneous chiral symmetry breaking is one of the most important features in low-energy QCD. The chiral symmetry is expected to be restored at very high temperature and/or density. Accompanied by the chiral phase transition, properties of hadrons will be changed especially near the critical point. The study of the phenomena associated with the chiral phase transition will give us some clues on the connection between the chiral symmetry and the low-energy hadron dynamics. We develop the theory based on the hidden local symmetry (HLS) at finite temperature, which is an effective field theory of QCD and includes pions and vector mesons as the dynamical degrees of freedom, and study the chiral phase transition in hot matter. We show that the chiral symmetry is restored as the vector manifestation (VM), in which the massless degenerate pion (and its flavor partners) and the longitudinal $\rho$ meson (and its flavor partners) as the chiral partner. We also present several predictions based on the VM. We estimate the critical temperature $T_c$ and show the following phenomena near $T_c$: the vector charge susceptibility becomes equal to the axial-vector charge susceptibility; the vector dominance of the electromagnetic form factor of the pion is largely violated; the pion velocity is close to the speed of light. Furthermore, we show that the remnant of the VM can be clearly seen in the system of heavy mesons. We expect that the VM and its predictions are testable by current and future experiments and the lattice analysis.