Radiative decay of hadronic molecule state for quarks

Using the general form of the generalized Bethe-Salpeter wave functions for four-quark states describing the meson-meson molecular structure given in our previous work, we obtain the general formulas for the decay widths of molecular states composed of two vector mesons with arbitrary spin and parity into two photons. Then this general formalism is applied to investigate the radiative two-photon decay of the obeserved \emph{X}(3915) state, where this exotic state \emph{X}(3915) is considered as a molecular state consisting of two heavy vector mesons $D^{\ast 0}{\bar{D}}^{\ast 0}$. The numerical result of decay mode $\mathit{\text{X}}(3915)\to \gamma \gamma$ is consistent with the experimental values.