Second order corrections to the muon lifetime and the semileptonic B decay

In this article two-loop QED corrections to the muon decay and corrections of order alpha(s)(2) to the semileptonic decay of the bottom quark are cons idered. We compute the imaginary part of the four-loop diagrams contributin g to the corresponding fermion propagator in the limit of small external mo mentum. The on-shell condition is obtained with the help of a conformal map ping and Fade approximation. Via this method we confirm the existing result s by an independent calculation. (C) 1999 Published by Elsevier Science B.V . All rights reserved.