Spatial particle condensation for an exclusion process on a ring

We study the stationary state of a simple exclusion process on a ring which was recently introduced by Arndt et al. (J. Phys. A 31 (1998) L45; J. Stat. Phys. 97 (1999) 1). This model exhibits spatial condensation of particles. It has been argued (J. Phys. A 31 (1998) L45; cond-mat/9809123) that the model has a phase transition from a “mixed phase” to a “disordered phase”. However, in this paper exact calculations are presented which, we believe, show that in the framework of a grand canonical ensemble there is no such phase transition. An analysis of the fluctuations in the particle density strongly suggests that the same result also holds for the canonical ensemble and suggests the existence of extremely long (but finite) correlation lengths (for example 1070 sites) in the infinite system at moderate parameter values in the mixed regime.