Microscopic dynamics of a phase transition: equilibrium vs out-of-equilibrium regime

We present for the first time to the nuclear physics community the Hamilton ian Mean Field (HMF) model. The model can be solved analytically in the can onical ensemble and shows a second-order phase transition in the thermodyna mic limit. Numerical microcanonical simulations show interesting features i n the out-of-equilibrium regime: in particular the model has a negative spe cific heat. The potential relevance for nuclear multifragmentation is discu ssed.