A Nekhoroshev type theorem for the nonlinear Schr\"odinger equation on the d-dimensional torus.

TL;DR

This paper proves a Nekhoroshev type stability result for the nonlinear Schrödinger equation on a d-dimensional torus, showing solutions with small analytic initial data remain stable and analytic for very long times.

Contribution

It establishes a Nekhoroshev type theorem for the nonlinear Schrödinger equation with typical smooth potential, demonstrating long-time stability of solutions with small analytic initial data.

Findings

Solutions remain analytic in a reduced strip for long times

Boundedness of solutions is proportional to initial data size

Long stability time scales as a power of inverse initial data size

Abstract

We prove a Nekhoroshev type theorem for the nonlinear Schr\"odinger equation $$ iu_t=-\Delta u+V\star u+\partial_{\bar u}g(u,\bar u)\, \quad x\in \T^d, $$ where $V$ is a typical smooth potential and $g$ is analytic in both variables. More precisely we prove that if the initial datum is analytic in a strip of width $\rho>0$ with a bound on this strip equals to $\eps$ then, if $\eps$ is small enough, the solution of the nonlinear Schr\"odinger equation above remains analytic in a strip of width $\rho/2$ and bounded on this strip by $C\eps$ during very long time of order $ \eps^{-\alpha|\ln \eps|^\beta}$ for some constants $C> 0$, $\alpha>0$ and $\beta<1$.