Theory of the pi+ pi- atom
Abstract
The 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 tau1=(3.03 0.10)× 10-15~s.
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