Two-tag correlation functions in one-dimensional lattice gases

Correlations between two labelled particles are studied in a one-dimensional lattice gas with nearest neighbour hopping. Fluctuations in the distance between the first particle (at time t) and the other (at time 0) are studied analytically and by Monte Carlo, with unbiased and biased hopping. In the latter case, the tag-tag correlation shows a nonmonotonic dependence on t. A stochastic harmonic theory, based on an exact mapping to an interface model, suggests a scaling form for the correlation as a function of t and the difference between the labels. Monte Carlo data are consistent with scaling. In the unbiased case, the scaling function given by the harmonic theory seems to be exact.