Structure of Near-Threshold s-Wave Resonances

Understand

We study the structure of two-body s-wave bound states as well as resonances in the threshold energy region.

• We focus on the single-channel scattering where the scattering length and the effective range are given by real numbers.
• It is shown that, in the energy region where the effective range expansion is valid, the properties of resonances are constrained only by the position of the pole.
• We find that the compositeness defined through the analytic continuation of the field renormalization constant is pure imaginary and normalized for resonances.