CHIRAL RESTORATION, FLAVOR SYMMETRY AND THE AXIAL ANOMALY AT FINITE TEMPERATURE IN AN EFFECTIVE THEORY

We investigate the equilibrium state and the mesonic excited states of hadronic matter at finite temperature T, using a generalized Nambu-Jona-Lasinio model as an effective theory of QCD. The model embodies the explicit breaking of the flavor SU(f)(3) symmetry and the U(A)(1) anomaly. It is shown that the SU(f)(3) symmetry already ceases being a good symmetry, even in an approximate manner, at rather small temperatures (T approximately 150 MeV). The imaginary-time formalism is adopted to investigate the mesonic excitations. Properties of the kaon at finite T are examined rather extensively. The thermodynamical potential as the finite-T effective potential is calculated in the mean-field approximation a la BCS. The entropy and the internal energy are also computed. It is shown that the screening masses of pions and sigma mesons coincide with the real masses in the chiral limit.