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

Abstract

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 though 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.