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. (C) 2001 Published by Elsevier Science B.V.