MEAN-FIELD APPROACH TO THE INSTANTON-INDUCED EFFECTS CLOSE TO THE QCDPHASE-TRANSITION

It was suggested earlier that the chiral phase transition is driven by a transition from random instanton-anti-instanton liquid to correlate d instanton-anti-instanton molecules. So far this phenomenon was studi ed by numerical simulations, while we develop an alternative semianaly tic approach. For two massless quark flavors, both instantons and ''mo lecules'' generate specific four-fermion effective interactions. After those are derived, we determine the temperature dependence of the the rmodynamic quantities, the quark condensate, and the fraction of molec ules using the standard mean field method. Using the Bethe-Salpeter eq uation, we calculate the T-dependence of mesonic correlation functions . These results shed new light on the problem of modification of hadro ns, and they can be tested directly in lattice simulations.