Multispecies pair annihilation reactions -: art. no. 250601

We consider diffusion-limited reactions A(i)+A(j)--> empty set (1less than or equal toi<jless than or equal toq) in d space dimensions. For q>2 and dgreater than or equal to2, we argue that the asymptotic density decay for such mutual annihilation processes with equal rates and initial densities is the same as for single-species pair annihilation A+A--> empty set. In d=1, however, particle segregation occurs for all q<infinity. The total density decays according to a q dependent power law, rho(t)similar tot(-alpha(q)). Within a simplified version of the model alpha(q)=(q-1)/2q can be determined exactly. Our findings are supported through Monte Carlo simulations.