Abstract:
In this paper we employed the BSE methed to study the leptonic decays of -meson. By using lowest-order Feynman diagrams, detailed derivations of the invariant matrix element were made. The Feynman rules and trace algebra have been employed in constructing the relativistic quantum mechanical expression of invariant amplitude. To this process we also calculate the pion invariant scattering amplitude of the two leptonic decay modes of the negatively charged pion using Feynman rules, decay width for the two leptonic decay of -meson and the ratio of two leptonic decay modes.
