  A simple two-species asymmetric exclusion model in one dimension with bulk
and boundary exchanges of particles is investigated for the existence of
spontaneous symmetry breaking. The model is a generalization of the bridge
model for which earlier studies have confirmed the existence of symmetry-broken
phases, and the motivation here is to check the robustness of the observed
symmetry breaking with respect to additional dynamical moves, in particular,
the boundary exchange of the two species of particles. Our analysis, based on
general considerations, mean-field approximation and numerical simulations,
shows that the symmetry breaking in the bridge model is sustained for a range
of values of the boundary exchange rate. Moreover, the mechanism through which
symmetry is broken is similar to that in the bridge model. Our analysis allows
us to plot the complete phase diagram of the model, demarcating regions of
symmetric and symmetry-broken phases.
