Chiral symmetry constraints on meson exchange current contributions to the pion DCX scattering

We study chiral symmetry constraints on the Meson Exchange Current (MEC) contributions to the pion-nucleus Double Charge Exchange (DCX) scattering at low energies, employing the Wess-Zumino model. This allows us to include ρ and α1 as well as pions in the exchange current. We find: (1) The πN interactions are equivalent to those of Olsson and Turner, and are therefore consistent with our previous DCX work. (2) As in the case of the pion MEC, chiral symmetry leads to the existence of a class of diagrams for the π and/or α1 MEC whose contributions tend to cancel each other and which therefore must be calculated simultaneously. (3) Because of the cancellation the summed effects of the ρ or α1 MEC are much smaller than those of the pion MEC. These results verify in detail the argument given in our earlier paper for the dominance of ion over vector meson MEC in DCX