Dimension of the singular set of wild H\"older solutions of the incompressible Euler equations

TL;DR

This paper investigates the size of the singular set in time for non-energy-conserving weak solutions of the incompressible Euler equations with Hölder regularity below 1/3, establishing lower bounds on its Hausdorff dimension and constructing solutions with controlled singular sets.

Contribution

It provides a lower bound on the Hausdorff dimension of the singular set for Hölder solutions and constructs solutions with specific singular set dimensions, advancing understanding of wild solutions and non-uniqueness.

Findings

Lower bound on Hausdorff dimension of singular times: 2β/(1−β).

Construction of solutions with singular set dimension ≤ 1/2 + (1/2)(2β′/(1−β′)).

Non-uniqueness of Hölder solutions from smooth initial data.

Abstract

For $\beta<\frac13$, we consider $C^\beta(\mathbb{T}^3\times [0,T])$ weak solutions of the incompressible Euler equations that do not conserve the kinetic energy. We prove that for such solutions the closed and non-empty set of singular times $\mathcal{B}$ satisfies $\dim_{\mathcal{H}}(\mathcal{B})\geq \frac{2\beta}{1-\beta}$. This lower bound on the Hausdorff dimension of the singular set in time is intrinsically linked to the H\"older regularity of the kinetic energy and we conjecture it to be sharp. As a first step in this direction, for every $\beta<\beta'<\frac{1}{3}$ we are able to construct, via a convex integration scheme, non-conservative $C^\beta(\mathbb{T}^3\times [0,T])$ weak solutions of the incompressible Euler system such that $\dim_{\mathcal{H}}(\mathcal{B})\leq \frac{1}{2}+\frac{1}{2}\frac{2\beta'}{1-\beta'}$. The structure of the wild solutions that we build allows moreover to deduce non-uniqueness of $C^\beta(\mathbb{T}^3\times [0,T])$ weak solutions of the Cauchy problem for Euler from every smooth initial datum.