Gravitational Origin of Quark Masses in an Extra-Dimensional Brane World
  Using the warped extra dimension geometry of the many-brane extension of the Randall-Sundrum solution, we find a natural explanation for the observed quark masses of the three Standard Model (SM) generations. Localizing massless SM matter generations on neighboring 3-branes in an extra dimensional world leads to phenomenologically acceptable effective four dimensional masses arising from the coupling of the fermion field with the background metric. Thus this geometry can simultaneously address the gauge and quark mass hierarchy problems. 
David Dooling and Kyungsik Kang