Low Energy Data and a Model of Flavor Mixing
  We consider a model in which the third family fermions are subjected to an SU(2) interaction different from the first two family fermions. Constrained by the Z-pole data, the heavy gauge boson mass is bounded from below to be about 1.7 TeV at the $2\sigma$ level. In this model, the flavor mixing between $\tau$ and $\mu$ can be so large that $Br(\tau\to \mu \bar{\nu_\mu} \nu_\tau)/ Br(\tau\to e \bar{\nu_e} \nu_\tau)$ and $Br(\tau\to \mu \mu \mu)$ provide a better constraint than the LEP/SLC data in some region of parameter space. Furthermore, flavor-changing neutral currents are unavoidable in the quark sector of the model. Significant effects to the $B^0-\bar{B^0}$ mixing and the rare decays of the $K$ and $B$ mesons, such as $K^\pm \to \pi^\pm \nu {\bar \nu}, b \to s \nu {\bar \nu}, B_s \to \tau^+\tau^-, \mu^+\mu^-$ and $B_{s,d} \to \mu^\pm \tau^\mp$, are expected. 
Ehab Malkawi and C.-P. Yuan