Analysis of blow-ups for the double obstacle problem in dimension two

TL;DR

This paper characterizes blow-up solutions for a double obstacle problem in two dimensions, introducing double-cone solutions, proving uniqueness of blow-ups, and analyzing free boundary regularity.

Contribution

It provides a complete classification of blow-up solutions, including a new double-cone type, and studies free boundary regularity in the two-dimensional double obstacle problem.

Findings

Existence of double-cone blow-up solutions.

Uniqueness of blow-up limits.

Free boundary near double-cone solutions consists of four $C^{1,eta}$ curves.

Abstract

In this article we study a normalised double obstacle problem with polynomial obstacles $ p^1\leq p^2$ under the assumption that $ p^1(x)=p^2(x)$ iff $ x=0$. In dimension two we give a complete characterisation of blow-up solutions depending on the coefficients of the polynomials $p^1, p^2$. In particular, we see that there exists a new type of blow-ups, that we call double-cone solutions since the coincidence sets $\{u=p^1\}$ and $\{u=p^2\}$ are cones with a common vertex. We prove the uniqueness of blow-up limits, and analyse the regularity of the free boundary in dimension two. In particular we show that if the solution to the double obstacle problem has a double-cone blow-up limit at the origin, then locally the free boundary consists of four $C^{1,\gamma}$-curves, meeting at the origin. In the end we give an example of a three-dimensional double-cone solution.