Nucleon-Antinucleon Mechanism for Pion-Pion Scattering Resonances

The Chew-Mandelstam $\frac{N}{D}$ equations for pion-pion scattering were modified to include contributions from the nucleon-antinucleon intermediate state, which was estimated in perturbation theory as well as by limitations imposed by unitarity alone. It was found that the Frazer resonance could not be obtained by such a simple mechanism, starting from $S$-wave dominant solutions.