Rigidity and nonexistence of CMC hypersurfaces in 5-manifolds

We prove that the nonnegative $3$-intermediate Ricci curvature and uniformly positive k-triRic curvature implies rigidity of complete noncompact two-sided stable minimal hypersurfaces in a Riemannian manifold (X⁵,g) with bounded geometry. The nonnegativity of $3$-intermediate Ricci curvature can be replaced by nonnegative Ricci and biRic curvature. In particular, there is no complete noncompact finite index CMC hypersurface in a closed $5$-dimensional manifold with positive sectional curvature. It extends result of Chodosh-Li-Stryker [to appear in J. Eur. Math. Soc (2024)] to $5$-dimensions. We also prove that complete constant mean curvature hypersurfaces in hyperbolic space H⁵ with finite index and the mean curvature greater than √658 must be compact. This improves the previous larger bound √175√148 on the mean curvature.