Phases of dense quarks at large Nc

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 similar to 1, and a hot phase of deconfined quarks and gluons, with pressure similar to N-c(2). When the quark chemical potential mu similar to 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 similar to 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 similar to 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. Published by Elsevier B.V.