2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/47010The perturbative framework is developed for the calculation of the pi(+)pi(-) atom characteristics (energy level shift and lifetime) on the basis of the field-theoretical Bethe-Salpeter approach. A closed expression for the first-order correction to the pi(+)pi(-) atom lifetime has been obtained.11 pages, LaTeX-file (elsart.sty)High Energy Physics - Phenomenologytext