Spinodal and dynamical instabilities at the phase transition from the quark-gluon plasma to hadrons

The stability of an expanding parton plasma is analyzed within quasi-particle models. The effective mass of the parton is calculated self-consistently from a gap equation which is either obtained from the Nambu Jona-Lasinio Lagrangian or from a fit to observables calculated on the lattice. The latter shows an effective confinement. At thermal equilibrium the stability is studied within thermodynamics (mechanical stability) and via a linear response analysis of the Vlasov equation. The instabilities related to a first-order phase transition are found. For a plasma expanding in three and one dimensions far from equilibrium a new type of instability, called dynamical, appears. The relation to cluster formation is shown in a molecular dynamics calculation.