Second Order Corrections to the Muon Lifetime and the Semileptonic B Decay

Abstract

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 considered. We compute the imaginary part of the four-loop diagrams contributing to the corresponding fermion propagator in the limit of small external momentum. The on-shell condition is obtained with the help of a conformal mapping and Padé approximation. Via this method we confirm the existing results by an independent calculation.

Comments: LaTeX, 11 pages, 1 figure