Extended technicolor contribution to the Zbb vertex

Abstract

We show that the flavor-diagonal gauge boson of the extended technicolor theory contributes with opposite sign to the standard model correction for the $Zbb$ vertex. This mechanism can naturally explain the deviation of the LEP result from the standard model prediction for the partial width $\Gamma(Z \rightarrow b{\bar b})$. A smaller value of the QCD coupling, $\alpha_s(m_Z) \simeq 0.115$, is then preferred by the $\Gamma(Z \rightarrow \mbox{hadron})$ data, which is consistent with both the recent Lattice-QCD estimate and the Particle Data Group average.