Chiral phase transition and dynamical properties of quarks at finite temperature and density

The properties of quarks in hot and/or dense matter are studied using the Nambu-Jona-Lasinio model with instanton effects. Thermo-field dynamics is applied to this model as a useful framework to present the unified description of quarks and nuclear matters at zero and non-zero temperatures. Especially, a four-dimensional cut-off parameter can be introduced transparently. The framework of this thermo-field dynamics is also discussed. We study the chiral symmetry in a finite temperature and/or density system. The dynamical quark masses are obtained up to a temperature of T=400 MeV and a density of 10 times of the nuclear saturation density for nuclear and neutron matters. Furthermore, we examine the instanton effects in the nuclear medium and discuss anti ss content in the nucleon for nuclear and neutron matters. (orig.)