2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/48089We give the modern derivation of Deser's formula using analytic continuation of the scattering amplitude as a function of momentum. The electromagnetic corrections to the pionium lifetime are given as evaluated in a potential model.8 pages, LaTeX-file (dubna98.sty) Talk given at the International Workshop "Hadronic Atoms and Posirtonium in the Standard Model", 26-31 May 1998, Dubna, RussiaHigh Energy Physics - Phenomenologytext