Near-threshold hadron scattering with effective field theory

When an exotic hadron locates near the threshold with the channel couplings, the internal structure of the exotic hadron is related to the scattering length. To incorporate the threshold effect, the Flatté amplitude has been often used to determine the scattering length. It is however known that an additional constraint is imposed on the Flatte amplitude near the threshold. We discuss this problem by using the effective field theory for the coupled-channel scattering.