Deconfinement and Chiral Restoration in Hot and Dense Matter

It is widely accepted that Quantum Chromodynamics (QCD) has phase transitions at high temperature, the nature of which depends on the quark mass, mq. In the limit of mq = 0, QCD has chiral symmetry, SUL(Nf)× SUR(Nf), in the case of Nf flavors, that spontaneously breaks into SUV(Nf) at low temperatures. The chiral condensate, 〈q̄q〉, serves as an order parameter for chiral restoration at high temperature. Since the quark mass term breaks chiral symmetry, mq/fπ is regarded as the magnitude of the explicit chiral symmetry breaking. When mq = ∞, on the other hand, there is no dynamical quark and thus no remnant of chiral symmetry at all. QCD is reduced to a pure gluonic theory, which has center symmetry at finite temperature, that is Z(Nc) for Nc colors. The order parameter is given by the Polyakov loop, 〈l〉 = 〈trL〉 = 〈trT e ∫