Thursday, June 19th - h. 15:00

Aula Seminari (A34)

P.Q. Hung
Virginia Univ., Charlottesville

Petite Unification of quarks and leptons:
twenty two years after


A recent surge of interest in the early unification of quarks and leptons, has prompted Buras and Hung to revive a paper written twenty two years ago by Hung, Buras and Bjorken. In that paper, a general discussion of quark-lepton unification characterized by the gauge group G_S x G_W with two couplings g_S and g_W and by the unification mass scales 10 TeV - 1000 TeV was provided.

The constraint from sin2(theta_W) restricts the choices for G_W and our favorite model was chosen to be SU(4)_PS x SU(2)4.
We review the main results of Hung-Buras-Bjorken, update the original SU(4)_PS x SU(2)4 model and propose two new models based on the groups SU(4)_PS x SU(2)3 and SU(4)_PS x SU(3)2, for which the consistency with the measured value of sin2(theta_W) determines the unification
scale to be roughly 1 TeV and 3-10 TeV, respectively.
The implications of this very early unification is the existence of new quarks and leptons with charges up to 4/3 (for quarks) and 2 (for leptons) and masses O(250 GeV).
Interestingly, in these models the rare decay K_L -> mu e is automatically absent at tree level and the one-loop contributions are consistent with the experimental upper bound.



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MCD, 13/6/03