STOCHASTIC RESONANCE IN A MEAN-FIELD MODEL OF COOPERATIVE BEHAVIOR

We study the long-time response of a stochastic system formed by very many interacting subsystems coupled by a mean-field interaction and su bject to a time periodic external field. In the absence of a driving f ield, the system shows an order-disorder phase transition and its time evolution is well described by a Fokker-Planck equation which is nonl inear in the probability density. We carry out an analysis of the dyna mics in the case of a weak driving field by means of a perturbation an alysis (Linear response theory). The response of the system is then gi ven in terms of a generalized susceptibility. Its evaluation shows tha t the phenomenon of stochastic resonance, typical of driven bistable s ystems, is greatly enhanced by the dynamical feedback induced by mean- field coupling.