Fluctuation effects in an epidemic model - art. no. 056103

We study a discrete epidemic model A + B --> 2A in one anti two dimensions (1D and 2D). In 1D for low concentration theta, we find that a depletion zo ne exists ahead of the front and the average velocity of the front approach es upsilon = theta /2. In the 1D high concentration limit, we find that the velocity approaches upsilon = 1 - e(-theta /2). In 2D, for low concentrati on we also find a depletion zone, and the velocity scales as upsilon simila r to theta (0.6), which is different from the scaling expected from the mea n field approximation, upsilon similar to theta (0.5). Analysis of the inte rface width scaling properties demonstrated that the front dynamics of this reaction are not governed by the Kardar-Parisi-Zhang equation.