Bounds to the mean curvature of leaves of CMC foliations

TL;DR

This paper extends classical results on the mean curvature of leaves in CMC foliations by considering Ricci curvature bounds, establishing bounds and rigidity results for the mean curvature in compact Riemannian manifolds.

Contribution

It generalizes previous results by Barbosa, Kenmotsu, and Oshikiri to cases with Ricci curvature bounded below, providing new bounds and characterizations of leaves in CMC foliations.

Findings

If |H| ≥ √K₀, then |H| ≡ √K₀ and leaves are totally umbilical.

If |H| ≤ √K₀, then the mean curvature is bounded above by √K₀.

Existence of a leaf with |H|=√K₀ implies either all leaves are totally geodesic or there is a totally umbilical leaf.

Abstract

The main goal of this present paper is to bring the results proved by Barbosa, Kenmotsu and Oshikiri (1991) and its ideas to a perspective where the Ricci curvature is bounded from below. For instance, for a foliation by CMC hypersurfaces on a compact (without boundary) Riemannian manifold $M^{n+1}$ with Ricci curvature bounded from below by $-nK_0\leq 0$ and such that the mean curvature $H$ of the leaves of the foliation satisfies $|H|\geq \sqrt{K_0}$, we prove that $|H|\equiv \sqrt{K_0}$ and all the leaves are totally umbilical. This gives, in particular, a generalization for the result proved by Barbosa, Kenmotsu and Oshikiri (1991), where the above result was proved in the case $K_0=0$. We also obtain a proof of the following: for a foliation by CMC hypersurfaces on a compact (without boundary) Riemannian manifold $M$ with Ricci curvature bounded from below by $-nK_0\leq 0$, the mean curvature $H$ of the leaves of the foliation satisfies $|H|\leq \sqrt{K_0}$. Furthermore, if the foliation contains a leaf $L$ whose absolute mean curvature is $|H_L|=\sqrt{K_0}$, then either $K_0=0$ and all the leaves of $\mathfrak{F}$ are totally geodesic, or $K_0>0$ and there is a totally umbilical leaf.