====== TTP96-05 Two-loop QCD corrections to $b\to c$ transitions at zero recoil ======
 
 
   <hidden TTP96-05  Two-loop QCD corrections to $b\to c$ transitions at zero recoil > Complete two-loop QCD corrections to $b\to c$ transitions are
 presented in the limit of zero recoil.  Vector and axial-vector
 coefficients $\eta_{A,V}$ are calculated analytically in the limit of
 equal beauty and charm masses, and a series appoximation is obtained
 for the general mass case.  $\eta_A$ is crucial for the determination
 of the absolute value of the Cabibbo-Kobayashi-Maskawa matrix element
 $V_{cb}$.  The two-loop effects enhance the one-loop corrections by
 21\%, removing a major theoretical uncertainty in the value of
 $|V_{cb}|$.  Including two-loop QCD effects and 
 previously neglected electroweak and Coulomb
 corrections we find $|V_{cb}| = 0.0379 \pm 0.0020({\rm stat})
 \pm 0.0025({\rm syst}) \pm 0.0011({\rm theory})$.
 </hidden>
|**Andrzej Czarnecki**  | 
|** Phys. Rev. Lett. 76 4124 1996  **  |
| {{preprints:1996:ttp96-05.pdf|PDF}} {{preprints:1996:ttp96-05.ps|PostScript}} [[http://arxiv.org/abs/hep-ph/9603261|arXiv]]   |
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