New Physics in the Third Family and its Effect on Low Energy Data

Abstract

We investigate, in detail, a model in which the third family fermions are subjected to an SU(2) dynamics different from the first two families. Constrained by the precision Z-pole data, the heavy gauge boson mass is bounded from below to be about 1.7 TeV at the $2\sigma$ level. The flavor-changing neutral current (FCNC) in the lepton sector can be significant in $\tau \leftrightarrow e$ and $\tau \leftrightarrow \mu$ transitions. In the latter case, the ratio $Br(\tau \to \mu \overline{{\nu }_{\mu }}{\nu }_{\tau })/Br(\tau \to e\overline{{\nu }_e}{\nu }_{\tau })$ and $Br(\tau \to \mu \mu \mu )$ can constrain the model better than LEP/SLC data in some region of the parameter space. Furthermore, FCNCs are unavoidable in the quark sector. Significant effects to the $B^0-\overline{B^0}$ 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.

Comments: 42 pages, Latex, 2 ps figures