  Thermodynamics and the phase structure of the Polyakov loop-extended two
flavor chiral quark-meson model (PQM) are explored. The analysis of the PQM
model is based on the functional renormalization group (FRG) method. An
appropriate truncation of the effective action with quarks coupled to
background gluonic fields is introduced. Within this scheme, we derive the
renormalization group flow equation for the scale-dependent thermodynamic
potential at finite temperature and density in the presence of a symmetry
breaking external field. The influence of fluctuations and of the background
gluon field on the properties of net-quark number density fluctuations and
their higher moments is explored. We study the dependence of the kurtosis of
quark number fluctuations on the pion mass and show that, in the presence of a
symmetry breaking term, the fluctuations lead to a smoothing of observables
near the crossover transition.
