The intrinsic metric of constant mean curvature surfaces and minimal hypersurfaces with free boundary
Lucas Ambrozio
TL;DR
The work revisits Ricci-Curbastro's intrinsic criteria for representing a surface metric as the first fundamental form of a (CMC) immersion into space forms and extends these ideas to constant mean curvature surfaces that meet umbilical boundaries orthogonally, including a Lawson-type free boundary correspondence. In dimension two, it shows that for an immersion with constant mean curvature $H$ into $\mathbb{Q}^3(c)$, the quantity $c+H^2-K$ is non-negative and the rescaled metric $\sqrt{c+H^2-K}\,g$ is flat away from the zero set of the traceless part $\mathring{A}$ of the second fundamental form, providing an intrinsic criterion for local immersion. The results generalize to higher dimensions via the dCaj framework, introducing an intrinsic tensor $\overline{g}=c(n-1)g-Ric_g$ and a factorisation with $A\circ A$, to obtain local minimal immersions into $\mathbb{Q}^{n+1}(c)$ with free boundary along umbilical boundaries; a corresponding boundary Lawson-type correspondence links spaces with the same $c+H^2$. The paper also develops intrinsic properties such as Ricci surfaces with boundary and connects these to Steklov eigenvalue problems for free boundary minimal surfaces, highlighting spectral aspects of the geometry. Overall, it provides a coherent intrinsic approach to free boundary CMC/minimal surfaces, their higher-dimensional generalisations, and related spectral phenomena.
Abstract
Ricci-Curbastro established necessary and sufficient conditions for a Riemannian metric on a surface to be the first fundamental form of a minimal immersion of that surface into the Euclidean space. We revisit certain developments arising from his theorem, and propose new versions of these results in the context of the theory of constant mean curvature surfaces in three-dimensional space forms that meet umbilical surfaces orthogonally along their boundary components. Higher dimensional generalisations, inspired by a theorem of do Carmo and Dajczer, are discussed as well.
