M. Velkovsky et E. Shuryak, MEAN-FIELD APPROACH TO THE INSTANTON-INDUCED EFFECTS CLOSE TO THE QCDPHASE-TRANSITION, Physical review. D. Particles and fields, 56(5), 1997, pp. 2766-2777
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.