Bhatnagar, Shashank (PhD)Mengesha, Yikdem2018-07-102023-11-092018-07-102023-11-092009-07http://10.90.10.223:4000/handle/123456789/7454The Bethe-Salpeter equation (BSE) provides a non-perturbativ method of treating the relativistic two-particle bound state problems on the basis of covariant instantaneous ansatz (CIA). On this basis, the structure of the hadron-quark vertex function 􀀀(ˆq) of vector mesons is derived from a QCD motivated Bethe-salpeter (BS) frame work and it is generalized to include various Dirac covariants (other than i .") 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. We study vector meson decay constants with inclusion of both the leading order (LO) and the next-to-leading order (NLO) Dirac Covariants, in addition to i .", in the Hadron-Quark vertex function 􀀀(ˆq) from their complete set on the basis of power counting rule through the frame work of BSE under covariant instantaneous ansatzenBoth Lo And Nlo Dirac CovariantsThesis