Regularity of soap film-like surfaces spanning graphs in a Riemannian manifold

Abstract

Let $M$ be an $n$-dimensional complete simply connected Riemannian manifold with sectional curvature bounded above by a nonpositive constant $-\kappa^2$. Using the cone total curvature $TC(\Gamma)$ of a graph $\Gamma$ which was introduced by Gulliver and Yamada Math. Z. 2006, we prove that the density at any point of a soap film-like surface $\Sigma$ spanning a graph $\Gamma \subset M$ is less than or equal to $\frac{1}{2\pi}\{TC(\Gamma) - \kappa^{2}\area(p\mbox{$\times\hspace*{-0.178cm}\times$}\Gamma)\}$. From this density estimate we obtain the regularity theorems for soap film-like surfaces spanning graphs with small total curvature. In particular, when $n=3$, this density estimate implies that if \begin{eqnarray*} TC(\Gamma) < 3.649\pi + \kappa^2 \inf_{p\in M} \area({p\mbox{$\times\hspace*{-0.178cm}\times$}\Gamma}), \end{eqnarray*} then the only possible singularities of a piecewise smooth $(\mathbf{M},0,\delta)$-minimizing set $\Sigma$ is the $Y$-singularity cone. In a manifold with sectional curvature bounded above by $b^2$ and diameter bounded by $\pi/b$, we obtain similar results for any soap film-like surfaces spanning a graph with the corresponding bound on cone total curvature.