Sharp Hadamard local well-posedness, enhanced uniqueness and pointwise continuation criterion for the incompressible free boundary Euler equations

TL;DR

This paper establishes a comprehensive local well-posedness theory for the free boundary incompressible Euler equations, including continuous dependence, enhanced uniqueness, stability bounds, refined energy estimates, and a sharp continuation criterion, all in low regularity Sobolev spaces.

Contribution

It provides the first complete local well-posedness framework with continuous dependence and a sharp continuation criterion for free boundary Euler equations in low regularity Sobolev spaces.

Findings

Proved local existence, uniqueness, and continuous dependence in Sobolev spaces.

Established a sharp continuation criterion based on pointwise norms.

Constructed a nonlinear functional to measure solution distances and proved their propagation.

Abstract

We provide a complete local well-posedness theory in $H^s$ based Sobolev spaces for the free boundary incompressible Euler equations with zero surface tension on a connected fluid domain. Our well-posedness theory includes: (i) Local well-posedness in the Hadamard sense, i.e., local existence, uniqueness, and the first proof of continuous dependence on the data, all in low regularity Sobolev spaces; (ii) Enhanced uniqueness: Our uniqueness result holds at the level of the Lipschitz norm of the velocity and the $C^{1,\frac{1}{2}}$ regularity of the free surface; (iii) Stability bounds: We construct a nonlinear functional which measures, in a suitable sense, the distance between two solutions (even when defined on different domains) and we show that this distance is propagated by the flow; (iv) Energy estimates: We prove refined, essentially scale invariant energy estimates for solutions, relying on a newly constructed family of elliptic estimates; (v) Continuation criterion: We give the first proof of a sharp continuation criterion in the physically relevant pointwise norms, at the level of scaling. In essence, we show that solutions can be continued as long as the velocity is in $L_T^1W^{1,\infty}$ and the free surface is in $L_T^1C^{1,\frac{1}{2}}$, which is at the same level as the Beale-Kato-Majda criterion for the boundaryless case; (vi) A novel proof of the construction of regular solutions. Our entire approach is in the Eulerian framework and can be adapted to work in more general fluid domains.