Sharp well-posedness for the cubic NLS and mKdV in $H^s(\mathbb{R})$

Abstract

We prove that the cubic nonlinear Schrödinger equation (both focusing and defocusing) is globally well-posed in $H^s(\mathbb{R})$ for any regularity $s>-\frac{1}{2}$. Well-posedness has long been known for $s\ge 0$, see [55], but not previously for any $s<0$. The scaling-critical value $s=-\frac{1}{2}$ is necessarily excluded here, since instantaneous norm inflation is known to occur [11, 40, 48]. We also prove (in a parallel fashion) well-posedness of the real- and complex-valued modified Korteweg-de Vries equations in $H^s(\mathbb{R})$ for any $s>-\frac{1}{2}$. The best regularity achieved previously was $s\ge \frac{1}{4}$; see [15, 24, 33, 39]. To overcome the failure of uniform continuity of the data-to-solution map, we employ the method of commuting flows introduced in [37]. In stark contrast with our arguments in [37], an essential ingredient in this paper is the demonstration of a local smoothing effect for both equations. Despite the non-perturbative nature of the well-posedness, the gain of derivatives matches that of the underlying linear equation. To compensate for the local nature of the smoothing estimates, we also demonstrate tightness of orbits. The proofs of both local smoothing and tightness rely on our discovery of a new one-parameter family of coercive microscopic conservation laws that remain meaningful at this low regularity.

arXiv comment88 pages

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Cited by in corpus (5)

• On the well-posedness problem for the derivative nonlinear Schrödinger equation
• Global well-posedness for the cubic nonlinear Schr{ö}dinger equation with initial lying in $L^p$-based Sobolev spaces
• Sharp well-posedness results of the Benjamin-Ono equation in $H^s(\mathbb{T},\mathbb{R})$ and qualitative properties of its solution
• KdV on an incoming tide
• Multisolitons for the cubic NLS in 1-d and their stability