Almost Sure Global Well-posedness for Fractional Cubic Schr\"odinger equation on torus

TL;DR

This paper establishes almost sure global well-posedness for the fractional cubic Schrödinger equation on the torus by constructing an invariant measure, extending the known well-posedness range for certain fractional orders.

Contribution

It introduces an invariant measure on $H^s$ for $s< ext{something}$, bridging the gap between local and global well-posedness in an almost sure sense for $rac{2}{3}< ext{something}$.

Findings

Invariant measure $$ on $H^s$ for $s< ext{something}$

Almost sure global well-posedness for $rac{1- ext{ extit{alpha}}}{2}< ext{ extit{alpha}}-rac{1}{2}$

Fills the gap between local and global well-posedness ranges

Abstract

In [12], we proved that $1$-d periodic fractional Schr\"odinger equation with cubic nonlinearity is locally well-posed in $H^s$ for $s>\frac{1-\alpha}{2}$ and globally well-posed for $s>\frac{5\alpha-1}{6}$. In this paper we define an invariant probability measure $\mu$ on $H^s$ for $s<\alpha-\frac{1}{2}$, so that for any $\epsilon>0$ there is a set $\Omega\subset H^s$ such that $\mu(\Omega^c)<\epsilon$ and the equation is globally well-posed for initial data in $\Omega$. We see that this fills the gap between the local well-posedness and the global well-posedness range in almost sure sense for $\frac{1-\alpha}{2}<\alpha-\frac{1}{2}$, i.e. $\alpha>\frac{2}{3}$ in almost sure sense.