Hierarchical Quark Masses and Small Mixing Angles from Warped   Intersecting Brane Models
  We propose a novel mechanism for reproducing the realistic hierarchical structure of the observed CKM mixing matrix and quark masses by means of introducing a warped metric. We illustrate the method on the basis of a specific Type IIA intersecting brane model proposed by Ibanez et al. The model is compactified on a direct product of three tori, on which four D-brane stacks wrap, and the intersections between two stacks collectively provide three generations of quarks and leptons. The exponential of the area formed by the intersection points corresponding to three matter fields is interpreted as the Yukawa coupling among them. It is known, however, that the Yukawa matrices for quarks are generically singular, and that it does not give definite mixing angles nor hierarchically suppressed quark masses. We show that the newly introduced warp effect on the internal manifold modifies the Yukawa matrix elements and generate hierarchical quark masses and CKM mixing angles. 
Tatsuya Noguchi (Tohoku U.)