Boundary behavior in the Loewner-Nirenberg problem

TL;DR

This paper proves that the hyperbolic radius associated with the maximal solution of a specific nonlinear PDE in a smooth bounded domain is sufficiently regular up to the boundary, using a reduction to a Fuchsian elliptic PDE.

Contribution

It establishes the boundary regularity of the hyperbolic radius in the Loewner-Nirenberg problem for dimensions three and higher.

Findings

Hyperbolic radius is $C^{2+eta}$ up to the boundary.

Reduction to a nonlinear Fuchsian elliptic PDE is effective.

Boundary regularity holds for domains of class $C^{2+eta}$.

Abstract

Let $\Omega\subset\mathbb R^n$ be a bounded domain of class $C^{2+\alpha}$, $0<\alpha<1$. We show that if $n\geq 3$ and $u_\Omega$ is the maximal solution of equation $\Delta u = n(n-2)u^{(n+2)/(n-2)}$ in $\Omega$, then the hyperbolic radius $v_\Omega=u_\Omega^{-2/(n-2)}$ is of class $C^{2+\alpha}$ up to the boundary. The argument rests on a reduction to a nonlinear Fuchsian elliptic PDE.