Coupling of pion condensate, chiral condensate, and Polyakov loop in an extended Nambu-Jona-Lasinio model

The Nambu-Jona-Lasinio model with a Polyakov loop is extended to the finite isospin chemical potential case, which is characterized by the simultaneous coupling of the pion condensate, chiral condensate, and Polyakov loop. The pion condensate, chiral condensate, and Polyakov loop as functions of temperature and isospin chemical potential are investigated by minimizing the thermodynamic potential of the system. The resulting (T,mu(I)) phase diagram is studied with emphasis on the critical point and Polyakov loop dynamics. The tricritical point for the pion superfluidity phase transition is confirmed, and the phase transition for isospin symmetry restoration in the high isospin chemical potential region perfectly coincides with the crossover phase transition for the Polyakov loop. These results agree with the lattice QCD data.