INTERACTING INSTANTON LIQUID IN QCD AT ZERO AND FINITE TEMPERATURES

In this paper we study the statistical mechanics of the instanton liqu id in QCD. After introducing the partition function as well as the gau ge-field- and quark-induced interactions between instantons, we descri be a method to calculate the free energy of the instanton system. We u se this method to determine the equilibrium density and the equation o f state from numerical simulations of the instanton ensemble in QCD fo r various numbers of flavors. We find that there is a critical number of flavors above which chiral symmetry is restored in the ground state . In the physical case of two light and one intermediate mass flavors, the system undergoes a chiral phase transition at T similar or equal to 125 MeV. We show that the mechanism for this transition is a rearra ngement of the instanton liquid, going from a disordered, random phase at low temperatures to a strongly correlated. molecular phase at high temperature. We also study the behavior of mesonic susceptibilities n ear the phase transition.