CHIRAL PHASES OF QCD AT FINITE-DENSITY AND TEMPERATURE

Chiral transitions in QCD at finite temperature and density are discus sed within a composite operator formalism. For massless quarks the pha se diagram in temperature and chemical potentials presents a tricritic al point at the intersection of the critical line for first-order phas e transitions and second-order transitions. The overall picture is not sensibly affected by small quark masses, except that the quark conden sate no longer vanishes for large temperatures and/or chemical potenti als, and for first-order transitions it remains discontinuous only for small quark mass values. Such effects are discussed by Clausius-Clape yron-like relations. The Landau expansion is used around the tricritic al point and for second-order transitions.