THE SUPER LONG-TIME DECAY OF VELOCITY FLUCTUATIONS IN A 2-DIMENSIONALFLUID

We have calculated the velocity autocorrelation function for a tracer particle in a model two-dimensional fluid. The fluid was represented b y a lattice Boltzmann equation with imposed fluctuations. By choosing a low Boltzmann diffusion coefficient for the tracer, the diverging co ntribution to the diffusion coefficient can be made to exceed the Bolt zmann value even at short times. We were thus able to find evidence fo r the renormalized, or 'super long-time', decay of the VACF in a two-d imensional fluid. We find quantitative evidence far the 1/root In(t) d ecay predicted by theory.