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 observed X ( 3915 ) state, in which this exotic state X ( 3915 ) is considered as a mixed state of two components D * 0 ¯ D * 0 and D * + D * − . The numerical result of decay mode X ( 3915 ) → γ γ is consistent with the experimental values.