2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/48454The relativistic perturbative approach based on the Bethe-Salpeter (BS) equation is developed for the study of the characteristics of the hadronic pi+ pi- atom. The general expression for the atom lifetime is derived. Lowest-order corrections to the relativistic Deser-type formula for the atom lifetime are evaluated within the Chiral Perturbation Theory. The lifetime of the pi+ pi- atom in the two-loop order of the Chiral Perturbation Theory is predicted to be tau_1=(3.03\pm 0.10)\times 10^{-15}~s.6 pages, LaTeX-file (article.sty), Talk given at the XIV International Seminar On High Energy Physics Problems "RELATIVISTIC NUCLEAR PHYSICS AND QUANTUM CHROMODYNAMICS",Dubna Aug. 17-22,1998High Energy Physics - Phenomenologytext