Nonuniversal correction to Z-->bb-bar and flavor-changing neutral current couplings.

Abstract

A nonuniversal interaction, which involves only the heavy quarks (${\mathit{t}}_{\mathit{L}}$,${\mathit{b}}_{\mathit{L}}$) and ${\mathit{t}}_{\mathit{R}}$, modifies the neutral current couplings and induces flavor-changing neutral currents (FCNC's). The size of the FCNC effect depends crucially on the dynamics of the fermion mass generation. In this paper, we study the effect of the nonuniversal interaction on Zbb\ifmmode\bar\else\textasciimacron\fi{}, Zbs\ifmmode\bar\else\textasciimacron\fi{}, Zds\ifmmode\bar\else\textasciimacron\fi{}, and Zdb\ifmmode\bar\else\textasciimacron\fi{}, by using an effective Lagrangian technique and assuming the quark mass matrices in the form of a generalized Fritzsch Ansatz. We point out that, if fitting ${\mathit{R}}_{\mathit{b}}$=\ensuremath{\Gamma}(Z\ensuremath{\rightarrow}bb\ifmmode\bar\else\textasciimacron\fi{})/\ensuremath{\Gamma}(Z\ensuremath{\rightarrow}hadrons) to the CERN LEP data within 1\ensuremath{\sigma}, the induced FCNC couplings are very close to the allowed bounds of several rare decays.