QCD AT HIGH BARYON DENSITY AND TEMPERATURE - COMPETING CONDENSATES AND THE CRITICAL-POINT

The phase diagram of strongly interacting matter is explored as a func tion of temperature and baryon number density. We investigate the poss ible simultaneous formation of condensates in the conventional quark-a nti-quark channel (breaking chiral symmetry) and in a quark-quark chan nel leading to color superconductivity: the spontaneous breaking of co lor symmetry via the formation of quark Cooper pairs. We point out tha t for two massless quark flavors a tricritical point in the phase diag ram separates a chiral symmetry restoring first order transition at hi gh densities from the second order transition at high temperatures. Aw ay from the chiral limit this tricritical point becomes a second order phase transition with Ising model exponents, suggesting that a long c orrelation length may develop in heavy ion collisions in which the pha se transition is traversed at the appropriate density.