Production of $π^{+}π^{-}$ pairs in diffractive photon-proton and in proton-proton collisions revisited, in particular concerning the Drell-Söding contribution

We discuss the exclusive photoproduction of $π^{+}π^{-}$ pairs in photon-proton and in proton-proton collisions at high energies. The $ρ^{0}$, $ω$, $f_{2}(1270)$, and non-resonant (Drell-Söding) contributions are considered. The calculation is based on the tensor-pomeron model. In the Drell-Söding c