Quark and Lepton Flavor Mixings in the SU(5) Grand Unification Theory
  We explain the imbalance of the flavor mixing angles between the quark and the lepton sectors in the context of the SU(5) GUT with the see-saw mechanism. The quark masses and the CKM matrix elements are obtained by using, respectively, the Fritzsch and Branco - Silva-Marcos form for the up- and down-quark Yukawa matrices (y^u and y^d) at the GUT scale. The charged-lepton Yukawa matrix (y^e) is the transpose of y^d, modified by the Georgi-Jarlskog factor. We show that the neutrino masses and mixing angles suggested by the recent solar and atmospheric neutrinos are then obtained from a simple texture of the neutrino Yukawa matrix (y^\nu) and a diagonal right-handed Majorana mass matrix at the GUT scale. 
K. Hagiwara and N. Okamura (Theory Group, KEK)