Fermi-Pasta-Ulam beta lattice: Peierls equation and anomalous heat conductivity.

The Peierls equation is considered for the Fermi-Pasta-Ulam beta lattice. Explicit form of the linearized collision operator is obtained. Using this form the decay rate of the normal-mode energy as a function of wave vector k is estimated to be proportional to k(5/3). This leads to the t(-3/5) long-time behavior of the current correlation function, and, therefore, to the divergent coefficient of heat conductivity. These results are in good agreement with the results of recent computer simulations. Compared to the results obtained through the mode coupling theory our estimations give the same k dependence of the decay rate but a different temperature dependence. Using our estimations we argue that adding a harmonic on-site potential to the Fermi-Pasta-Ulam beta lattice may lead to finite heat conductivity in this model.