# Shashank Bhatnagar

## Publications Authored By Shashank Bhatnagar

In this work we study the radiative decay widths of vector quarkonia for the process of $J/\psi(nS)\rightarrow\eta_{c}(nS)\gamma$ and $\Upsilon(nS)\rightarrow\eta_{b}(nS)\gamma$ (for principal quantum numbers $n=1, 2, 3$) in the framework of Bethe-Salpeter equation under the covariant instantaneous ansatz using a $4\times 4$ form of BSE. The parameters of the framework were determined by a fit to the mass spectrum of ground states of pseudoscalar and vector quarkonia, such as; $\eta_{c}$, $\eta_{b}$, $J/\psi$ and $\Upsilon$. These input parameters so fixed were found to give good agreements with data on mass spectra of ground and excited states of pseudoscalar and vector quarkonia, leptonic decay constants of pseudoscalar and vector quarkonia, two photon decays and two gluon decays of pseudoscalar quarkonia in our recent paper. Read More

In this work we calculate the mass spectrum of charmonium and bottomonium for $1P,... Read More

In this work we calculate the mass spectrum, weak decay constants, two photon decay widths, and two gluon decay widths of ground (1S), and radially excited (2S,3S,... Read More

In this work, we investigate the spectroscopy and decay rates of charmonia within the framework of non-relativistic Schr\"{o}dinger equation by employing an approximate inter quark-antiquark potential. The spin hyperfine, spin-orbit and tensor components of the one gluon exchange interaction are employed to compute the spectroscopy of the excited S states and few low-lying P and D waves. The resultant wave functions at zero inter quark separation as well as some finite separation are employed to predict the di-gamma, di-leptonic and di-gluon decay rates of charmonia states by using the conventional Van Royen-Weisskopf formula. Read More

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: $\rho$, $\omega$, $\phi$, $\psi$ and $Y$ through the process $V\rightarrow\gamma*\rightarrow e^+ + e^-$. We employ the generalized structure of hadron-quark vertex function $\Gamma$ 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. Read More

In this work we study the process $e^{+}+e^{-}\longrightarrow J/\Psi+\eta_{c} $ at energy $\sqrt{s}= 10.6 GeV$ observed recently at B-factories whose measurements were made by Babar and Belle groups. We calculate the cross section for this process in the Bethe-salpeter formalism under Covariant Instantaneous Anstaz (CIA). Read More

We have employed the framework of Bethe-Salpeter equation under covariant instantaneous ansatz to calculate leptonic decay constants of unequal mass pseudoscalar mesons like pi, K, D, Ds and B and radiative decay constants of neutral pseudoscalar mesons like pi and etac in two photon decays of these mesons. In the Dirac structure of hadronic BS wave function, the covariants are incorporated from their complete set in accordance with a recently proposed power counting rule, order-by-order in powers of inverse of meson mass. The decay constants are calculated with the incorporation of both Leading order (LO) and the Next-to-leading order (NLO) Dirac covariants. Read More

We employ the framework of Bethe-Salpeter equation under Covariant Instantaneous Ansatz to study the leptonic decays of pseudoscalar mesons. The Dirac structure of hadron-quark vertex function $\Gamma $ is generalized to include various Dirac covariants besides $\gamma_5 $ from their complete set. The covariants are incorporated in accordance with a power counting rule, order by order in powers of the inverse of the meson mass. Read More

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. Read More