{ "id": "1605.06602", "version": "v1", "published": "2016-05-21T07:34:31.000Z", "updated": "2016-05-21T07:34:31.000Z", "title": "Mean curvature in manifolds with Ricci curvature bounded from below", "authors": [ "Jaigyoung Choe", "Ailana Fraser" ], "comment": "12 pages", "categories": [ "math.DG" ], "abstract": "Let $M$ be a compact Riemannian manifold of nonnegative Ricci curvature and $\\Sigma$ a compact embedded 2-sided minimal hypersurface in $M$. It is proved that there is a dichotomy: If $\\Sigma$ does not separate $M$ then $\\Sigma$ is totally geodesic and $M\\setminus\\Sigma$ is isometric to the Riemannian product $\\Sigma\\times(a,b)$, and if $\\Sigma$ separates $M$ then the map $i_*:\\pi_1(\\Sigma)\\rightarrow \\pi_1(M)$ induced by inclusion is surjective. This surjectivity is also proved for a compact 2-sided hypersurface with mean curvature $H\\geq(n-1)\\sqrt{k}$ in a manifold of Ricci curvature $Ric_M\\geq-(n-1)k,k>0$, and for a free boundary minimal hypersurface in a manifold of nonnegative Ricci curvature with nonempty strictly convex boundary. As an application it is shown that a compact $n$-dimensional manifold $N$ with the number of generators of $\\pi_1(N)