Cyclically coupled spreading and pair annihilation

Recently it has been shown that the transition of the (1 + 1)-dimensional a nnihilation-fission process 2X --> 3X, 2X --> O exhibits an unusual type of nonequilibrium critical behavior. The phenomenological properties of criti cal clusters are characterized by two different dynamic modes for spreading and diffusion. In order to describe the interplay of these modes, we intro duce an effective model which involves two species of particles A and B. Th e A-particles perform an ordinary directed percolation process while the B particles diffuse and annihilate. Both subsystems are cyclically coupled by particle transmutation A reversible arrow B. The resulting critical behavi or is in many respects similar to the one observed in the annihilation-fiss ion process. (C) 2001 Elsevier Science B.V. All rights reserved.