Further geometry of the mean curvature one-form and the normal plane field one-form on a foliated Riemannian manifold

摘要

For foliations on Riemannian manifolds, we develop elementary geometric and topological properties of the mean curvature one-form ?o and the normal plane field one-form ?2. Through examples, we show that an important result of Kamber-Tondeur on ?o is in general a best possible result. But we demonstrate that their bundle-like hypothesis can be relaxed somewhat in codimension 2. We study the structure of umbilic foliations in this more general context and in our final section establish some analogous results for flows.