S-matrix poles near the ΛN and ΣN thresholds in the coupled ΛN-ΣN system -: art. no. 024003

We search t-matrix poles for Lambda N-Sigma N coupling interactions using two soft core models of the Nijmegen group which bind the hypertriton at the correct binding energy, and hard core models which are still influential in hypernuclear physics. To treat the hard core potentials, a useful method for calculating the off-shell t-matrix is proposed. We find poles close to the Sigma N threshold in the second or third quadrant of the complex plane of the Sigma N relative momentum. The relation between the poles and the shape of the Lambda N elastic total cross section is discussed based on a so-called uniformization by which two-channel t-matrices become single-valued on a complex valuable. We also find poles near the Lambda N threshold. These are correlated to the S-wave Lambda N scattering lengths, the values of which have yet to be determined. [S0556-2813(99)00908-5].