IRREVERSIBLE TRANSITIONS IN A 2 SPECIES BRANCHING ANNIHILATING RANDOMWALKER PROCESS

We introduce a branching annihilating random walker process with two s pecies, particles A and B, which diffuse creating particles of opposit e kind (A --> A + B, B --> B + A) and annihilating instantaneously (A + B --> 0) when they meet. The model is defined in a one dimensional d iscrete lattice. For particles A and B, the rate of jumping are p(A) a nd p(B), and the rate of branching (1 - p(A)) and (1 - p(B)), respecti vely (0 less than or equal to P-A, P-B less than or equal to 1) In the [p(A),p(B)]-plane it is found two different phases: the vacuum state and the active phase with finite density of particles. The system unde rgoes irreversible second order phase transitions between these states along a critical line. Monte Carlo results show that the transitions belong to the same universality class as directed percolation.