Phases of Dense Quarks at Large N_c

TL;DR

This paper explores the various phases of dense quark matter at large N_c, revealing a confined, chirally symmetric phase with baryon-like interactions near the Fermi surface, and discusses implications for QCD phase diagrams.

Contribution

It proposes a new phase of dense quark matter at large N_c with unique properties, including confinement and chiral symmetry restoration, expanding understanding of QCD phases.

Findings

Identification of a dense, confined phase with N_c pressure behavior.

Chiral symmetry can be both broken and restored in dense phases.

Baryons near the Fermi surface exhibit parity doubling.

Abstract

In the limit of a large number of colors, N_c, we suggest that gauge theories can exhibit several distinct phases at nonzero temperature and quark density. Two are familiar: a cold, dilute phase of confined hadrons, where the pressure is ~ 1, and a hot phase of deconfined quarks and gluons, with pressure ~ N_c^2. When the quark chemical potential mu ~ 1, the deconfining transition temperature, T_d, is independent of mu. For T < T_d, as mu increases above the mass threshold, baryons quickly form a dense phase where the pressure is ~ N_c. As illustrated by a Skyrme crystal, chiral symmetry can be both spontaneously broken, and then restored, in the dense phase. While the pressure is ~ N_c, like that of (non-ideal) quarks, the dense phase is still confined, with interactions near the Fermi surface those of baryons, and not of quarks. Thus in the chirally symmetric region, baryons near the Fermi surface are parity doubled. We suggest possible implications for the phase diagram of QCD.