Boson-triboson scattering with Yamaguchi potential. 1. Restriction to s-wave contribution from the 3+1-subamplitude

For the investigation of the S-wave boson-triboson phase shift, the Faddeev-Osborn equation is solved numerically by assuming a rank-one separable potential of the Yamaguchi type for the two-particle interaction. The calculation is performed in the exact approach based on rigorous Faddeev theory of the scattering problem. As a first step of the investigation, to gain insight into the origin of a four-body resonance, the contribution from the 3+1-subamplitude is limited to the s-wave only. The calculated phase shift behaves generally like a standard two-body one for a potential that causes one loosely bound state; this phase shift has further characteristic behavior resulting from fine structure consisting of a valley and a peak. The result of the partial cross section indicates the presence of two resonant states in the four-boson system with the Yamaguchi potential. (author)