ROLE OF FLUCTUATIONS FOR INHOMOGENEOUS REACTION-DIFFUSION PHENOMENA

Although fluctuations have been known to change the long-time behavior of homogeneous diffusion-reaction phenomena dramatically in dimensions d less-than-or-equal-to 4, simulations of reaction fronts in two-dimensional A + B --> C inhomogeneous systems have only shown marginal departure from mean-field behavior. We perform cellular-automata simulations of the one-dimensional case and find that the width W(t) of the reaction front behaves as t0.293 +/- 0.005, in contrast to mean-field behavior t1/6. We develop a scaling theory to obtain inequalities for the exponents in the more general mechanism nA + mB --> C. Heuristic arguments about the range of fluctuations imply that the mean-field behavior should be correct in dimensions larger than an upper critical dimension d(up) = 2, irrespective of the values of n and m. This leads us to reinterpret the two-dimensional data obtained previously in terms of a logarithmic correction to mean-field behavior.