General behavior of near-threshold hadron scattering for exotic hadrons

We discuss the general behavior of the near-threshold scattering amplitude with channel couplings. The signal of the exotic hadrons near the threshold may manifest as a dip structure in the cross section originated from a zero point of the scattering amplitude. Such a dip structure by the zero point cannot be reproduced by the Flatt\'{e} amplitude which is widely used for the analysis of exotic hadrons, because of the constraints imposed on the Flatt\'{e} amplitude near the threshold. In this work, we propose the General amplitude which can describe the dip structure near the threshold, in contrast to the Flatt\'{e} amplitude. Moreover, we numerically study the behavior of the near-threshold cross section in relation to the zero point.