Entropic contributions in Langevin equations for anisotropic driven systems

We report on analytical results for a series of anisotropic driven systems in the context of a recently proposed Langevin equation approach. In a rece nt paper (P.L. Garrido et al., Phys. Rev. E 61 (2000) R4683) we have pointe d out that entropic contributions, over-looked in previous works, are cruci al in order to obtain suitable Langevin descriptions of driven lattice gase s. Here, we present a more detailed derivation and justification of the ent ropic term for the standard driven lattice gas, and also we extend the impr oved approach to other anisotropic driven systems, namely: (i) the randomly driven lattice gas, (ii) the two-temperature model and, (iii) the bi-layer lattice gas, It is shown that the two-temperature model and the lattice ga s driven either by a random field or by an uniform infinite one are members of the same universality class. When the drive is uniform and finite the ' standard' theory is recovered. A Langevin equation describing the phenomeno logy of the bi-layer lattice gas is also presented. (C) 2001 Elsevier Scien ce B.V. All rights reserved.