  Using a chirally symmetric Lagrangian, which contains quarks as elementary
degrees of freedom and mesons as bound states, we investigate the expansion and
hadronization of a fireball, which initially contains only quarks and produces
mesons by collisions. For this model, we study the time scales of expansion and
thermal and chemical equilibration. We find that the expansion progresses
relatively fast, leaving not necessarily enough time to establish thermal and
chemical equilibrium. Mesons are produced in the bulk of the fireball rather
than at a surface, at a temperature below the Mott temperature. Initial density
fluctuations become amplified during the expansion. These observations
challenge the applicability of hydrodynamical approaches to the expansion of a
quark-gluon plasma.
