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The formula tan²θCmdmₛ is derived from a continuous symmetry. Cabibbo universality is guaranteed in a natural way. All weak mixing angles are determined in terms of quark masses. The b quark is predicted to decay mainly to the u quark, and the lifetime of the associated mesons is {~}10^-10-10^-11 sec. We argue that this additional symmetry is (essentially) the only one which can be added to the standard SUc(3)SU(2)U(1) model without generating anomalies.
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Wilczek et al. (1979) studied this question.
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