Temperature dependence of the chiral condensate from an interacting pion gas

By exploiting the fact that the chiral condensate is related to the derivative of the free-energy density with respect to the bare quark mass, the temperature dependence of the condensate ratio < anti qq>T/< anti qq>0 can be obtained from an interacting pion gas. Using the Weinberg Lagrangian at the Hartree level, a depression of the condensate with temperature is found. For T<mπ the results are in good agreement with chiral perturbation theory in the three loop approximation. Near Tc, however, there are marked differences due to the non-perturbative nature of the Hartree approximation. Model dependencies arising from ambiguities in the chiral symmetry-breaking Hamiltonian are being discussed. (orig.)