On free boundary minimal hypersurfaces in the Riemannian Schwarzschild space

TL;DR

This paper investigates the Morse index and geometric properties of free boundary minimal hypersurfaces in higher-dimensional Riemannian Schwarzschild spaces, revealing new existence, stability, and density results.

Contribution

It extends the understanding of free boundary minimal hypersurfaces to higher dimensions, showing zero Morse index for certain symmetric cases and existence of infinitely many non-congruent hypersurfaces with infinite Morse index.

Findings

Morse index of symmetric hypersurfaces is zero for n≥4.

Existence of non-compact, non-totally geodesic hypersurfaces with zero Morse index in n≥8.

Infinitely many non-congruent hypersurfaces with infinite Morse index for n≥4.

Abstract

In contrast with the 3-dimensional case (cf. \cite{RaMo}), where rotationally symmetric totally geodesic free boundary minimal surfaces have Morse index one; we prove in this work that the Morse index of a free boundary rotationally symmetric totally geodesic hypersurface of the $n$-dimensional Riemannnian Schwarzschild space with respect to variations that are tangential along the horizon is zero, for $n\geq4$. Moreover, we show that there exist non-compact free boundary minimal hypersurfaces which are not totally geodesic, $n\geq 8$, with Morse index equal to $0$. Also, it is shown that, for $n\geq4$, there exist infinitely many non-compact free boundary minimal hypersurfaces, which are not congruent to each other, with infinite Morse index. We also study the density at infinity of a free boundary minimal hypersurface with respect to a minimal cone constructed over a minimal hypersurface of the unit Euclidean sphere. We obtain a lower bound for the density in terms of the area of the boundary of the hypersurface and the area of the minimal hypersurface in the unit sphere. This lower bound is optimal in the sense that only minimal cones achieve it.