Phase transition in a triplet process
  We show that the reaction-diffusion process 3A -> 4A, 3A -> 2A exhibits a different type of continuous phase transition from an active into an absorbing phase. Because of the upper critical dimension d_c = 4/3 we expect the phase transition in 1+1 dimensions to be characterized by non-trivial fluctuation effects. 
Kwangho Park, Haye Hinrichsen, and In-mook Kim