Quark mixings in SU(6) x SU(2)_R and suppression of V_<ub>.

概要

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The quark mixing matrix V_<CKM> is studied in depth on the basis of superstring inspired SU(6)×SU(2)_R model with global flavor symmetries. The sizable mixings between right-handed down-type quark D^c and colored Higgs field g^c potentially occur but no such mixings in up-type quark sector. In the model the hierarchical pattern of V_<CKM> is understood systematically. It is shown that due to large D^c-g^c mixings V_<ub> is naturally suppressed compared to V_<td>. It is pointed out that the observed suppression of V_<ub> is in favor of the presence of SU(2)_R gauge symmetry but not in accord with generic SU(5) GUT.