Analytical methods in heavy quark physics and the case of ${\tau }_{1/2}(w)$

Abstract

Analytical methods in heavy quark physics are shortly reviewed, with emphasis on the problems of dynamical calculations. Then, attention is attracted to the various difficulties raised by a tentative experimental determination of ${\tau }_{1/2}$

Comments: 10 pages, FPCP2003 conference (Paris) [typos corrected,new references]