Perturbation Theory for Fermi-Pasta-Ulam Chains
Fermi-Pasta-Ulam chains have been an active research area since the famous simulations by Fermi, Pasta, and Ulam in the 1950s, which exhibited unexpected recurrence phenomena. Around the same time, new perturbation theory results began to be developed, which are now known as the KAM and Nekhoroshev theorems. These theorems provide stability results for slightly perturbed integrable systems, under appropriate conditions ...