  We study an effective theory for QCD at finite temperature and density which
contains the leading center symmetric and center symmetry breaking terms. The
effective theory is studied in a flux representation where the complex phase
problem is absent and the model becomes accessible to Monte Carlo techniques
also at finite chemical potential. We simulate the system using a generalized
Prokof'ev-Svistunov worm algorithm and compare the results to a low temperature
expansion. The phase diagram is determined as a function of temperature,
chemical potential and quark mass. Shape and quark mass dependence of the phase
boundaries are as expected for QCD. The transition into the deconfined phase is
smooth throughout, without any discontinuities or critical points.
