

Aula Seminari (A34) P.Q. Hung
Virginia Univ., Charlottesville Petite Unification of quarks and leptons: twenty two years after The constraint from sin^{2}(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 HungBurasBjorken, 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 sin^{2}(theta_W) determines the unification scale to be roughly 1 TeV and 310 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 oneloop contributions are consistent with the experimental upper bound. 