We discuss the QCD corrections to the large-$m_t$ electroweak contributions to $\Delta r$ and to the process $Z\to b \bar b$ as two of the most representative examples. This needs the construction of an effetive field theory below the top quark. We discuss the issue of what $\mu$ scale is the appropriate one at every stage and argue that, while matching corrections do verify the simple prescription of taking $\mu \simeq m_t$ in $\alpha_s(\mu)$, logarithmic (i.e. $\sim \log m_t$) corrections do not, and require the use of the running $\alpha_s(\mu)$ in the corresponding renormalization group equations. In particular we obtain the $\alpha_s$ correction to the non-universal $\log m_t$ contribution to the $Zb\bar b$ vertex.
- Pub Date:
- April 1995
- High Energy Physics - Phenomenology
- Latex with macro appended at the beginning of file. Talk given at the Ringberg Workshop ``Perspectives for electroweak interactions in $e^+e^-$ collisions", Ringberg Castle, Germany, February 5--8, 1995. To appear in the proceedings