Current quark mass and chiral-symmetry breaking in QCD at finite temperature in a mean-field approximation

The effects of current quark masses on chiral-symmetry breaking in QCD at finite temperature are examined using a mean-field approximation. The current quark mass plays a role analogous to that of an external magnetic field in the ferromagnetic transition, as it explicitly violates the chiral symmetry whose restoration characterizes the phase transition. For small enough masses, the order parameter, related to the quark condensate, maintains the features of the massless case up to the critical temperature, and then it approaches a constant value depending on the current mass term itself. The consequences on the behavior of the pion mass and decay constant are also studied. Our calculations are done with a variational composite operator approach. We also discuss the critical exponents (in temperature, mass, and for susceptibility) that follow in general from assuming the possible validity of a Landau mean-field theory.