Anomalous energy transport in the FPU‐β chain

We consider the energy current correlation function for the FPU‐β lattice. For small nonlinearity 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 N2/5 with the system size N.