Two photon decays of pion in Bethe–Salpeter framework with generalized structure of hadron-quark vertex

Two photon decays of pion are studied in the framework of the Bethe–Salpeter equation under Covariant Instantaneous Ansatz where the structure of hadron-quark vertex function Γ is generalized to include various Dirac covariants (other than γ₅) from their complete set. These covariants are incorporated in accordance with a power counting rule (which was recently employed to calculate leptonic decays constants of pseudoscalar mesons and vector mesons) order by order in powers of the inverse of the meson mass. Pion-photon coupling constant F_π is calculated with the incorporation of leading order covariants. (author)