Invariant measures and the soliton resolution conjecture

TL;DR

This paper introduces a statistical approach to the soliton resolution conjecture for the nonlinear Schrödinger equation by constructing approximate invariant measures, showing they concentrate on solitons in the continuum limit, thus providing a new perspective on the conjecture.

Contribution

It develops a novel probabilistic framework for the soliton resolution conjecture by constructing discrete measures that approximate an invariant measure, leading to insights into the long-term behavior of solutions.

Findings

Constructed a sequence of discrete measures approximating an invariant measure.

Proved the continuum limit of these measures concentrates on the ground state soliton.

Provided a tentative formulation and proof of the soliton resolution conjecture in a discrete setting.

Abstract

The soliton resolution conjecture for the focusing nonlinear Schrodinger equation (NLS) is the vaguely worded claim that a global solution of the NLS, for generic initial data, will eventually resolve into a radiation component that disperses like a linear solution, plus a localized component that behaves like a soliton or multi-soliton solution. Considered to be one of the fundamental open problems in the area of nonlinear dispersive equations, this conjecture has eluded a proof or even a precise formulation till date. This paper proves a "statistical version" of this conjecture at mass-subcritical nonlinearity, in the following sense. The uniform probability distribution on the set of all functions with a given mass and energy, if such a thing existed, would be a natural invariant measure for the NLS flow and would reflect the long-term behavior for "generic initial data" with that mass and energy. Unfortunately, such a probability measure does not exist. We circumvent this problem by constructing a sequence of discrete measures that, in principle, approximate this fictitious probability distribution as the grid size goes to zero. We then show that a continuum limit of this sequence of probability measures does exist in a certain sense, and in agreement with the soliton resolution conjecture, the limit measure concentrates on the unique ground state soliton. Combining this with results from ergodic theory, we present a tentative formulation and proof of the soliton resolution conjecture in the discrete setting.