Generalized structure of hadron-quark vertex function in Bethe-Salpeter   framework: Applications to leptonic decays of V-mesons
  We employ the framework of Bethe-Salpeter equation under Covariant Instantaneous Ansatz (CIA) to study the leptonic decays of vector mesons. The structure of hadron-quark vertex function Gamma is generalized to include various Dirac covariants (other than i gamma dot epsilon) from their complete set. They are incorporated in accordance with a naive power counting rule order by order in powers of the inverse of the meson mass. The decay constants for rho omega and phi mesons are calculated with the incorporation of leading order covariants. 
Shashank Bhatnagar and Shi-Yuan Li