Pion double charge exchange in a composite-meson model

The pion double charge exchange amplitude is evaluated in a composite-meson model based on the four-quark interaction. The model assumes that the mesons are two-quark systems and can interact with each other only through quark loops. To evaluate the meson exchange current contribution, the form factors of the two-pion decay modes of the ρ,σ, and f0 mesons have been used in the calculations. The contribution of the four-quark box diagram has been taken into account as well as a contact diagram. The contributions of the ρ,σ, and f0 mesons increase the forward scattering cross section, which depends weakly on the energy