Selfconsistent description of strongly interacting matter

Chiral symmetry restoration at nonzero temperature is studied in
the framework of the O(4) linear sigma model and the U(N_f)_r x
U(N_f)_l linear sigma model with N_f=2,3, and 4 quark flavors. We
investigate the temperature dependence of the masses of the scalar
and pseudoscalar mesons, and the non-strange, strange, and charm
condensates within the Hartree approximation as derived from the
Cornwall-Jackiw-Tomboulis formalism. We find that the masses of
the non-strange and strange mesons at nonzero temperature depend
sensitively on the particular symmetry of the model and the number
of light quark flavors N_f. On the other hand, due to the large
charm quark mass, neither do charmed mesons significantly affect
the properties of the other mesons, nor do their masses change
appreciably in the temperature range around the chiral symmetry
restoration temperature. In the chiral limit, the transition
temperatures for chiral symmetry restoration are surprisingly
close to those found in lattice QCD.