  We investigate the relaxational dynamics of the order parameter of chiral
symmetry breaking, the sigma mean-field, with a heat bath consisting of quarks
and antiquarks. A semiclassical stochastic Langevin equation of motion is
obtained from the linear sigma model with constituent quarks. The equilibration
of the system is studied for a first order phase transition and a critical
point, where a different behavior is found. At the first order phase transition
we observe the phase coexistence and at a critical point the phenomenon of
critical slowing down with large relaxation times. We go beyond existing
Langevin studies and include reheating of the heat bath by determining the
energy dissipation during the relaxational process. The energy of the entire
system is conserved. In a critical point scenario we again observe critical
slowing down.
