Constraint maps with free boundaries: the obstacle case

TL;DR

This paper investigates the regularity of constraint maps with free boundaries, revealing that the projected image is at most $C^{2,1}$ and establishing global $W^{3,BMO}$ regularity in arbitrary dimensions, with detailed analysis around singular points.

Contribution

It provides new regularity results for the projected image in constraint maps with free boundaries, especially in higher dimensions and near singular points, extending classical obstacle problem theory.

Findings

Projected image is at most $C^{2,1}$ regular.

Global $W^{3,BMO}$ regularity in arbitrary dimensions.

Detailed analysis of regularity near singular points in 2D.

Abstract

This paper revives a four-decade-old problem concerning regularity theory for (continuous) constraint maps with free boundaries. Dividing the map into two parts, the distance part and the projected image to the constraint, one can prove various properties for each component. As already pointed out in the literature, the distance part falls under the classical obstacle problem, which is well-studied by classical methods. A perplexing issue, untouched in the literature, is the properties of the projected image and its higher regularity, which we show to be at most of class $C^{2,1}$. In arbitrary dimensions, we prove that the image map is globally of class $W^{3,BMO}$, and locally of class $C^{2,1}$ around the regular part of the free boundary. The issue becomes more delicate around singular points, and we resolve it in two dimensions. In the appendix, we extend some of our results to what we call leaky maps.