Persistence of Invariant Tori for Stochastic Nonlinear Schrödinger in the Sense of Most Probable Paths

This paper investigates the application of KAM theory to the stochastic nonlinear Schrödinger equation on infinite lattices, focusing on the stability of low-dimensional invariant tori in the sense of most probable paths. For generality, we provide an abstract proof within the framework of stochastic Hamiltonian systems on infinite lattices. We begin by constructing the Onsager-Machlup functional for these systems in a weighted infinite sequence space. Using the Euler-Lagrange equation, we identify the most probable transition path of the system's trajectory under stochastic perturbations. Additionally, we establish a large deviation principle for the system and derive a rate function that quantifies the deviation of the system's trajectory from the most probable path, especially in rare events. Combining this with classical KAM theory for the nonlinear Schrödinger equation, we demonstrate the persistence of low-dimensional invariant tori under small deterministic and stochastic perturbations. Furthermore, we prove that the probability of the system's trajectory deviating from these tori can be described by the derived rate function, providing a new probabilistic framework for understanding the stability of stochastic Hamiltonian systems on infinite lattices.