  A general class of mass transport models with Q species of conserved mass is
considered. The models are defined on a lattice with parallel discrete time
update rules. For one-dimensional, totally asymmetric dynamics we derive
necessary and sufficient conditions on the mass transfer dynamics under which
the steady state factorises. We generalise the model to mass transfer on
arbitrary lattices and present sufficient conditions for factorisation. In both
cases, explicit results for random sequential update and continuous time limits
are given.

Statistical Mechanics