Bounds on the growth of high Sobolev norms of solutions to Nonlinear Schrodinger Equations on $S^1$

TL;DR

This paper establishes polynomial bounds on the growth of high Sobolev norms for solutions to nonlinear Schrödinger equations on the circle, using a novel frequency decomposition approach that extends to higher nonlinearities and non-integrable variants.

Contribution

It introduces a new iteration bound based on frequency decomposition, applicable to higher nonlinearities and non-integrable variants of NLS, surpassing previous methods.

Findings

Polynomial growth bounds for high Sobolev norms of NLS solutions.

Applicable to nonlinearities of degree ≥ 5 where previous techniques fail.

Improved bounds for modified cubic NLS equations with broken integrability.

Abstract

We consider Nonlinear Schrodinger type equations on $S^1$. In this paper, we obtain polynomial bounds on the growth in time of high Sobolev norms of their solutions. The key is to derive an iteration bound based on a frequency decomposition of the solution. This iteration bound is different than the one used earlier in the work of Bourgain, and is less dependent on the structure of the nonlinearity. We first look at the defocusing NLS equation with nonlinearity of degree $\geq 5$. For the quintic NLS, Bourgain derives stronger bounds using different techniques. However, our approach works for higher nonlinearities, where the techniques of Bourgain don't seem to apply. Furthermore, we study variants of the defocusing cubic NLS in which the complete integrability is broken. Among this class of equations, we consider in particular the Hartree Equation, with sufficiently regular convolution potential. For most of the equations that come from modifying the defocusing cubic NLS, we obtain better bounds than for the other equations due to the fact that we can use higher modified energies as in the work of the I-Team.