Contribution of meson exchange currents to pion double charge exchange at low energies.

Abstract

The magnitude of the effect of meson exchange currents on low-energy pion nucleus double charge exchange is reexamined. In particular, the role of chiral symmetry in limiting the size of the effect is studied, using the method of effective Lagrangians. The equivalence of two commonly used versions of the theory is shown, which resolves some of the disagreements in the literature. The effect is calculated for the case of $^{42}\mathrm{Ca}$, and found to be smaller than that of ordinary multiple scattering.