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We have employed the framework of Bethe-Salpeter equation under covariant instantaneous ansatz to calculate leptonic decay constants of unequal mass pseudoscalar mesons like π ± , K, D, D s and B and radiative decay constants of neutral pseudoscalar mesons like π 0 and η c in two photons.In the Dirac structure of hadronic Bethe-Salpeter wave function, the covariants are incorporated from their complete set in accordance with a recently proposed power counting rule. The decay constants are calculated with the incorporation of both Leading order and Next-to-leading order Dirac covariants. The results validate the power counting rule which provides a practical means of incorporating Dirac covariants in the Bethe-Salpeter wave function for a hadron.

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In this work we have employed Bethe-Salpeter equation (BSE) under covariant instantaneous ansatz (CIA) to study electromagnetic decays of ground state equal mass vector mesons: ρ, ω, φ, ψ and Y through the process V → γ * → e + +e − . We employ the generalized structure of hadron-quark vertex function Γ which incorporates various Dirac structures from their complete set order-by-order in powers of inverse of meson mass. The electromagnetic decay constants for the above mesons are calculated using the leading order (LO) and the next-to-leading order (NLO) Dirac structures. The relevance of various Dirac structures in this calculation is studied.