Effective models of two-flavor QCD: From small towards large mq

We study effective models of chiral fields and Polyakov loop expected to describe the dynamics responsible for the phase structure of two-flavor QCD. We consider the chiral sector described either using a linear sigma model or a Nambu-Jona-Lasinio model and study how these models, on the mean-field level when coupled with the Polyakov loop, behave as a function of increasing bare quark (or pion) mass. We find qualitatively similar behaviors for the cases of the linear sigma model and the Nambu-Jona-Lasinio model and, by comparing with existing lattice data, show that one cannot conclusively decide which of the two approximate symmetries drives the phase transitions at the physical point.