Majorana neutrinos with split fermions in extra dimensions
  We propose new solutions to the neutrino mass problem in theories with large extra dimensions in a thick wall scenario. It has recently been argued that our 3-brane could be a thick wall at the boundary of the bulk. The gauge bosons and the Higgs scalars have an almost flat profile on this wall, while fermions could have localized profile with left-handed and right-handed components displaced with respect to each other. We point out that with split fermions it is possible to generate Majorana neutrino masses contributing to the neutrinoless double beta decay. The almost degenerate neutrinos can also come out naturally in this case. Unlike other models of neutrino masses in extra dimensions there are no bulk fields in this scenario. 
H.V. Klapdor-Kleingrothaus and U. Sarkar