Tag diffusion in driven systems, growing interfaces and anomalous fluctuations

Tagged diffusion in a one-dimensional hard-core lattice gas with biased nearest-neighbor hopping is mapped to a model of a growing interface. Based on the Kardar-Parisi-Zhang theory of interface dynamics, it is suggested that fluctuations, in the separation of the initial position of a tagged particle from the position at time t of a particle with tag shifted by vt at time t, grow at t<SUP>½</SUP> for most v, and as t<SUP>1/3</SUP> for a critical v<SUB>c</SUB>. This is verified by numerical simulation, and the dependence of v<SUB>c</SUB> on bias and density is found. The t<SUP>¼</SUP> growth of fluctuations in the unbiased case is unstable with respect to both bias and v-v<SUB>c