Extra Dimensions and Compositeness as a Basis for Hierarchy in Quark   Mass Matrices
  Strong gauge and top-Yukawa couplings predicted in the presence of extra dimensions lead to a trickle-down effect of the top-coupling through the renormalization group equations for the quark Yukawa matrices. The matrix elements for the u and d-quarks get progressively smaller as one moves away from the dominant (33)-element revealing a hierarchical pattern for the mass matrices. 
Bipin R. Desai, Alexander R. Vaucher (University of California,   Riverside, CA)