Kinematic Interpretation of Exotic Forward ${\Delta }^{-}$ Production in $\mathrm{pn}\to {\Delta }^{-}p{\pi }^{+}$ and $\mathrm{pn}\to {\Delta }^{-}{\Delta }^{++}$ at High Energy

We provide a nonexotic, kinematic interpretation of forward ${\Delta }^{-}$ production in the reactions $\mathrm{pn}\to {\Delta }^{-}p{\pi }^{+}$ and $\mathrm{pn}\to {\Delta }^{-}{\Delta }^{++}$ at high energy. We show that forward production of ${\Delta }^{-}$ in ${\Delta }^{-}p{\pi }^{+}$ is mediated by a simple diagram which includes one-pion exchange plus low-energy, off-shell ${\pi }^{-}p\to {\pi }^{+}{\Delta }^{-}$ scattering. The final state $n{\pi }^{-}{\Delta }^{++}$ is produced by a similar one-pion—exchange diagram. The sum of these diagrams imitates $\mathrm{pn}\to {\Delta }^{-}{\Delta }^{++}$. Our approach has the virtue of absolute normalization; both shapes of distributions and total cross sections are in excellent agreement with available data. We discuss other reactions in which the same mechanism operates, and propose tests of our scheme.