Riemannian flow techniques on totally geodesic null hypersurfaces

We study the influence of the existence of totally geodesic null hypersurface on the properties of a Lorentzian manifold. By coupling the rigging technique with the existence of a null foliation we prove the existence of a Riemann flow structure which allows us to use powerful results to show how curvature conditions on the spacetime restricts its causal structure. We also study the existence of periodic null or spacelike geodesic.