  We consider the energy current correlation function for the FPU-beta lattice.
For small non-linearity one can rely on kinetic theory. The issue reduces then
to a spectral analysis of the linearized collision operator. We prove thereby
that, on the basis of kinetic theory, the energy current correlations decay in
time as t^(-3/5). It follows that the thermal conductivity is anomalous,
increasing as N^(2/5) with the system size N.
