Rescattering effects in three-particle states and the Schmid theorem

We discuss effects of anomalous singularities in three-meson production amplitudes which are caused by the triangle diagrams with resonance production in the intermediate state followed by the rescattering of outgoing particles. We show that the Schmid theorem [C. Schmid, Phys. Rev. 154 (1967) 1363] is not valid when the amplitude of the rescattering particles has several open channels. In this case the irregularities related to anomalous singularities appear not only in the three-particle Dalitz-plot but in the two-particle distributions as well. Examples of the processes pp̄ (at rest) → (three mesons) are discussed.