LANGEVIN EQUATION FOR DRIVEN DIFFUSIVE SYSTEMS

An open controversy exists about the nature of the second-order nonequ ilibrium phase transition exhibited by a lattice gas in which particle s are driven along one of the lattice directions by an external agent. Field theoretical predictions and Monte Carlo estimates for the criti cal exponent values do not seem to agree with each other. In this pape r we introduce a Langevin equation in which the effects of the microsc opic dynamics are carefully taken into account. We show that the order parameter critical exponent when the drive is infinite (no backwards jumps) is not mean-field-like, in contrast with the prediction for fin ite values of the drive. This finding seems to reconcile field theoret ical and numerical results.