Invariant Gibbs measures and global dynamics for fractional cubic Schrödinger equations on the torus

Abstract

We consider the defocusing Wick-ordered cubic fractional nonlinear Schrödinger equation on the two-dimensional torus with dispersion relation $ω(k)=|k|^α$. In the weakly dispersive regime $\frac{29}{15}<α<2$, we construct global dynamics for almost every initial datum with respect to the associated Gibbs measure as the limit of the finite-dimensional truncated flows and prove invariance of the Gibbs measure. The core of the proof is an almost sure local theory based on the method of random averaging operators (arXiv:1910.08492v2). The main new ingredients are fractional lattice counting estimates and localized random tensor bounds, which exploit the geometric structure of the fractional phase in place of the classical number-theoretic tools available for quadratic dispersion.