Perturbative framework for the pi(+)pi(-) atom
  The perturbative framework is developed for the calculation of the pi(+)pi(-) atom characteristics 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. 
V. E. Lyubovitskij (JINR, Dubna and Tomsk University), E. Z. Lipartia   (JINR, Dubna and Tbilisi University), A. G. Rusetsky...