Pseudoresonant Argand loops

Analytic properties of the partial wave scattering amplitudes are discussed. It is shown that the Argand plots for the partial wave amplitudes may exhibit resonance-like loops (pseudoresonances) for amplitudes that have no resonance pole but logarithmic branch points. Some examples are considered in detail. A simple test is suggested permitting to distinguish the pseudoresonant loops from the resonant ones. This test is based on the comparison of the radius of the loops for the forward and backward scattering amplitudes. The pseudoresonances are most likely to be in the KN and NN scattering and in the pion scattering on light nuclei