Top-Charm flavor changing contributions to the effective $bsZ$ vertex

Abstract

We analyze the effects of a tree level flavor changing $tcZ$ vertex induced by a mixing with new isosinglet $Q=2/3$ quarks, on the effective $bsZ$ vertex. We compute the contributions arising from the new electroweak penguin diagrams involving one insertion of the $tcZ$ vertex. We show that a generalized GIM mechanism ensures the cancellation of the mass independent terms as well as of the new divergences. Unexpectedly, the presence of a $tcZ$ coupling cannot enhance the rates for the $Z$ mediated flavor changing decays \bsll\ and \bsnn, implying that these processes cannot be used to set limits on the $tcZ$ coupling. The additional effects of the heavy isosinglets are compared with the well studied effects of new isodoublets appearing in multi-generational models.

12 pages, latex, 1 figure (uses LaTeX Routine FEYNMAN.TEX available from hep-ph archive)

References in corpus (2)

• Quark Singlets: Implications and Constraints
• Lepton Mass Matrix Models

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