Formal Solution of a Class of Reaction-Diffusion Models: Reduction to a   Single-Particle Problem
  We consider the trapping reaction A + B -> B in space dimension d<=2. By formally eliminating the B particles from the problem we derive an effective dynamics for the A particles from which the survival probability of a given A particle and the statistics of its spatial fluctuations can be calculated in a rather general way. The method can be extended to the study of annihilation/coalescence reactions, B + B -> 0 or B, in d=2. 
Alan J. Bray, Satya N. Majumdar, Richard A. Blythe