Chiral symmetry restoration at finite temperature and chemical potential in the improved ladder approximation

The chiral symmetry of QCD is studied at finite temperature and chemical potential using the Schwinger-Dyson equation in the improved ladder approximation. We calculate three order parameters: the vacuum expectation value of the quark bilinear operator, the pion decay constant, and the quark mass gap. We have a second order phase transition at the temperature $T_c=169\mathrm{}$ MeV along the zero chemical potential line, and a first order phase transition at the chemical potential ${\mu }_c=598\mathrm{}$ MeV along the zero temperature line. We also calculate the critical exponents of the three order parameters.