Δ33Dynamics in Pion Double Charge Exchange

The authors calculate effects of direct meson-${\Delta }_{33}$ interactions on pion double charge exchange to isobaric analog states in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$. Virtual ${\Delta }_{33}$'s in the ground, state are shown to contribute negligibly, contrary to recent expectations. On-shell ${\Delta }_{33}$ interactions can have a large effect through $\pi +\rho$ exchange, and inclusion of these terms improves agreement with experiment below resonance. Data at the higher energies cannot be explained by a simple combination of sequential pion-nucleon scattering plus direct meson-${\Delta }_{33}$ terms.