  A one-dimensional driven two-species model with parallel sublattice update
and open boundaries is considered. Although the microscopic many-body dynamics
is symmetric with respect to the two species and interactions are short-ranged,
there is a region in parameter space with broken symmetry in the steady state.
The sublattice update is deterministic in the bulk and allows for a detailed
analysis of the relaxation dynamics, so that symmetry breaking can be shown to
be the result of an amplification mechanism of fluctuations. In contrast to
previously considered models, this leads to a proof for spontaneous symmetry
breaking which is valid throughout the whole region in parameter space with a
symmetry broken steady state.
