Showing papers by "Jurgen Berndt published in 2014"

Cohomogeneity one actions on Minkowski spaces

Abstract: We study isometric cohomogeneity one actions on the (n+1)-dimensional Minkowski space up to orbit-equivalence. We give examples of isometric cohomogeneity one actions on the Minkowski space whose orbit spaces are non-Hausdorff. We show that there exist isometric cohomogeneity one actions on the Minkowski space which are orbit-equivalent on the complement of an n-dimensional degenerate subspace and not orbit-equivalent on this degenerate subspace. We classify isometric cohomogeneity one actions on 2- and 3-dimensional Minkowski spaces up to orbit-equivalence.

On the index of symmetric spaces

Abstract: Let M be an irreducible Riemannian symmetric space. The index of M is the minimal codimension of a (non-trivial) totally geodesic submanifold of M. We prove that the index is bounded from below by the rank of the symmetric space. We also classify the irreducible Riemannian symmetric spaces whose index is less or equal than 3.

Totally Geodesic Submanifolds of Riemannian Symmetric Spaces

Abstract: The index of a Riemannian manifold is defined as the minimal codimension of a totally geodesic submanifold. In this note we discuss two recent results by the author and Olmos (Berndt and Olmos, On the index of symmetric spaces, preprint, arXiv:1401.3585) and some related topics. The first result states that the index of an irreducible Riemannian symmetric space is bounded from below by the rank of the symmetric space. The second result is the classification of all irreducible Riemannian symmetric spaces of noncompact type whose index is less or equal than three.

Maximal totally geodesic submanifolds and index of symmetric spaces

Abstract: Let M be an irreducible Riemannian symmetric space. The index i(M) of M is the minimal codimension of a totally geodesic submanifold of M. In previous work the authors proved that i(M) is bounded from below by the rank rk(M) of M. In this paper we classify all irreducible Riemannian symmetric spaces M for which the equality holds, that is, rk(M) = i(M). In this context we also obtain an explicit classification of all non-semisimple maximal totally geodesic submanifolds in irreducible Riemannian symmetric spaces of noncompact type and show that they are closely related to irreducible symmetric R-spaces. We also determine the index of some symmetric spaces and classify the irreducible Riemannian symmetric spaces of noncompact type with i(M) = 4,5 or 6.