The phase diagram of the quark–meson model

Within the proper-time renormalization group approach, the chiral phase diagram of a two-flavor quark-meson model is studied. In the chiral limit, the location of the tricritical point which is linked to a Gaussian fixed point, is determined. For quark chemical potentials smaller than the tricritical one the second-order phase transition belongs to the O(4) universality class. For temperatures below the tricritical one we find initially a weak...