Fluctuations and instabilities in multifragmentation

In this article we review the foundations of dynamical description of unstable systems. We describe the concept of stochastic one-body theories. In particular, spinodal instabilities are accounted for: the most unstable dynamics and therefore the initial multifragmentation; the characteristic time scales for the growth of these modes and the typical time scales for cluster formation, as a function of the amplitude of fluctuations, are discussed. The differences between such a fragmentation pattern, essentially determined by the instabilities, and fragmentation structures obtained from the hypothesis of statistical equilibrium are stressed. Finally, we propose that the occurrence of spinodal instabilities can be signed by a lack of small size fragments associated to a tendency to break the system in close-mass pieces. (authors). 19 refs., 6 figs