Relaxation and overlap-probability function in the spherical and mean-spherical models.
The problem of the equivalence of the spherical and mean-spherical models, which has been thoroughly studied and is understood in equilibrium, is considered anew from the dynamical point of view during the time evolution following a quench from above to below the critical temperature. It is found that there exists a crossover time t(*) approximately V(2/d) such that for t<t(*) the two models are equivalent, while for t>t(*) macroscopic discrepancies arise. The relation between the off equilibrium response function and the structure of the equilibrium state that usually holds for phase ordering systems is found to hold for the spherical model but not for the mean-spherical one. The latter model offers an explicit example of a system which is not stochastically stable.
Fusco
Nicola
N
Istituto Nazionale per la Fisica della Materia, Unità di Salerno, Università di Salerno, 84081 Baronissi (Salerno), Italy. nicola.fusco@sa.infn.it
Zannetti
Marco
M