Covariant light-front approach for heavy quarkonium: decay constants, P   \to \gamma \gamma and V \to P \gamma
  The light-front approach is a relativistic quark model and offers many insights to the internal structures of the hadronic bound states. In this study, we apply the covariant light-front approach to ground-state heavy quarkonium. The pesudoscalar and vector meson decay constants are discussed. We present a detailed study of two-photon annihilation P \to \gamma \gamma and magnetic dipole transition V \to P \gamma processes. The numerical predictions of the light-front approach are consistent with the experimental data and those in other approaches. The relations of the light-front approach with the other methods are discussed in brief. 
Chien-Wen Hwang and Zheng-Tao Wei