General Reaction-Diffusion Processes With Separable Equations for Correlation Functions

We consider general multi-species models of reaction diffusion processes and obtain a set of constraints on the rates which give rise to closed systems of equations for correlation functions. Our results are valid in any dimension and on any type of lattice. We also show that under these conditions the evolution equations for two point functions at different times are also closed. As an example we introduce a class of two species models which may be useful for the description of voting processes or the spreading of epidemics.