Résumé en anglais

We consider an infinite system of cells coupled into a chain by a smooth nearest neighbour potential $\varepsilon V$. The uncoupled system (cells) evolve according to Hamiltonian dynamics perturbed stochastically with an energy conserving noise of strength $\zeta$. We study the Green-Kubo (GK) formula $\kappa(\varepsilon,\zeta)$ for the heat conductivity of this system which exists and is finite for $\zeta >0$, by formally expanding $\kappa(\varepsilon,\zeta)$ in a power series in $\varepsilon$, $\kappa(\varepsilon,\zeta) = \sum_{n\ge 2} \varepsilon^n \kappa_n(\zeta)$. We show that $\kappa_2(\zeta)$ is the same as the conductivity obtained in the weak coupling (van Hove) limit where time is rescaled as $\varepsilon^{-2}t$. $\kappa_2(\zeta)$ is conjectured to approach as $\zeta \to 0$ a value proportional to that obtained for the weak coupling limit of the purely Hamiltonian chain. We also show that the $\kappa_2(\zeta)$ from the GK formula, is the same as the one obtained from the flux of an open system in contact with Langevin reservoirs. Finally we show that the limit $\zeta\to 0$ of $\kappa_2(\zeta)$ is finite for the pinned anharmonic oscillators due to phase mixing caused by the non-resonating frequencies of the neighbouring cells. This limit is bounded for coupled rotors and vanishes for harmonic chain with random pinning.