  Fluctuations in the vicinity of a phase transition are important but
neglected in mean-field theory. In order to assess the influence of such
fluctuations on the critical endpoint and the size of the critical region in
the QCD phase diagram, a mean-field calculation of a two-flavor quark-meson
model is compared with a renormalization group approach. However, due to the
lack of confinement in this effective model the equation of state near the
chiral phase transition is still unrealistic. A first improvement of this model
can be achieved by coupling quark degrees of freedom to the Polyakov loop,
consequently incorporating certain aspects of confinement. The influence of
these modifications on the resulting phase diagram is discussed.
