The $Z\to b\bar{b}$ Excess and Top Decay

Abstract

The apparent excess of $Z\to b\bar{b}$ events at LEP may be an indication of new physics beyond the standard model. However, in either the two-Higgs-doublet model or the minimal supersymmetric standard model, any explanation would lead to an important new decay mode of the top quark and suppresses the $t\to Wb$ branching fraction, which goes against what has been observed at the Tevatron. In the two-Higgs-doublet model, the branching fraction of $Z\to b\bar{b}$ + a light boson which decays predominantly into $b\bar{b}$ would be at least of order 10${}^{-4}$.

Comments: 15 pages and 8 figures