The leptons νₑ, e, ν_μ, μ, ν_τ, τ, and analogously the quarks u, d, c, s, t, b, are unified within the Weinberg-Salam SU₂×{}U₁ gauge model without enlarging the gauge group. The result is a theory in which the familiar leptons, quarks, and gauge bosons, plus some extra Higgs bosons necessary for unification, all carry a new multiplicatively conserved quantum number π=±1. The most striking results of this unification are (1) π conservation forbids μ→eγ but allows the Higgs-boson-mediated decays τ→lγ (l=e or μ) and τ→μee or eμμ, at a calculable rate with a calculable lower limit; (2) for quarks, two of the three Cabibbo angles must be zero, so that the b quark (assumed lighter than t) decays only via Higgs-boson exchange, always semileptonically and always with lepton-number violation, e.g., b→de⁺μ^-. This singular prediction will confirm or exclude the model as soon as b-flavored mesons are discovered. These and other phenomenological consequences of this unification are explained, and rates are estimated.
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Emanuel Derman (1979) studied this question.