Intersecting hypersurfaces and Lovelock Gravity
  A theory of gravity in higher dimensions is considered. The usual Einstein-Hilbert action is supplemented with Lovelock terms, of higher order in the curvature tensor. These terms are important for the low energy action of string theories.   The intersection of hypersurfaces is studied in the Lovelock theory. The study is restricted to hypersurfaces of co-dimension 1, $(d-1)$-dimensional submanifolds in a $d$-dimensional space-time. It is found that exact thin shells of matter are admissible, with a mild form of curvature singularity: the first derivative of the metric is discontinuous across the surface. Also, with only this mild kind of curvature singularity, there is a possibility of matter localised on the intersections.   This gives a classical analogue of the intersecting brane-worlds in high energy String phenomenology. Such a possibility does not arise in the pure Einstein-Hilbert case. 
Steven Willison