The validity of certain phenomenological approaches to spin zero meson production in nucleon-nucleon collisions is considered. It is shown that, to first-order perturbation theory, a method analogous to the distorted wave approximation is valid. Comparison is made with a bremsstrahlung-like calculation which, for neutral mesons with non-derivative coupling to the spinor field, gives no production, since the nucleon recoil is neglected. Application of the distorted wave approach to neutral meson production in proton-neutron collisions, and comparison with the results for production of charged mesons in proton-proton collisions is sketched. Results are quoted for simple inverse processes.
η-meson production in nucleon-nucleon collisions within an effective Lagrangian model