Three fermionic generations on a topological defect in extra dimensions
  We suggest a mechanism explaining the origin of three generations of the Standard Model fermions from one generation in a higher-dimensional theory. Four-dimensional fermions appear as zero modes trapped in the core of a topological defect with topological number three. We discuss hierarchical pattern of masses and mixings which arises in these models. 
M.V. Libanov and S.V. Troitsky