Jost function description of elastic and few-body resonances

摘要

We discuss how the analysis of the zeros of the functions introduced by Jost in 1946,acting individually or collectively,provides a comprehensive framework for describing resonances in single and multichannel collisions.In particular,we propose a generalization of the Wigner threshold law that copes with some deviations recently observed in opening reaction channels.We also pay special attention to the appearance of zeros of the s-wave Jost function in the fourth quadrant of the complex momentum plane,as analysed by Nussenzveig in 1959 but erroneously ruled out in following studies.