Extended Technicolor Contribution to theZbbVertex

The deviation of the experimental value of $R_b \equiv \Gamma_b/\Gamma_h$from the standard-model prediction can be naturally explained in the extendedtechnicolor scenario.The diagonal extended technicolor gauge boson whichflavor-diagonally couples with both the ordinary fermions and thetechni-fermions plays an important role in order to have the appropriateradiative correction to the $Zbb$ vertex. But since the diagonal extendedtechnicolor gauge boson gives too large positive contribution to the $T$parameter, we need some new mechanisms which generate negative contribution tothe $T$ parameter.Comment: 9 pages. Postscript file (uuencoded Z-compressed .tar file created by csh script uufiles.) Proceedings of the talk given at Yukawa International Seminar'95, From the Standard Model to Grand Unified Theorie