On the diffusion of clusters of hard rods

It is shown that the diffusion coefficient of clusters of hard rods in one dimension is exactly independent of the number of rods comprising the cluster. An expression for the autocorrelation function of the velocity of the cluster centre of mass is obtained from a simple stochastic model, and asymptotically for large clusters from the exact autocorrelation function. Neither approximate nor exact velocity autocorrelation function decays exponentially for any size of cluster.