DYNAMICS OF UNSTABLE MATTER

The Validity of the mean-field approximation is tested in the spinodal region by comparing the predictions of the Boltzmann-Nordheim-Vlasov (BNV) equation for an expanding classical system to the exact solution given by Classical Molecular Dynamics. The two solutions show, outside the critical region, the same isentropic behaviour, but largely differ inside. The exact solution enters deeply inside the spinodal region and remains there, while the BNV solution enters and after some time goes back. For the BNV solution, we test in particular the effects of the collision term, of a surface term added to the mean-field and Boltzmann-Langevin type of fluctuations.