Structure of $f_0(980)$ from a coupled channel analysis of $S$-wave $\pi\pi$ scattering

Abstract.

A coupled channel model is used to study the nature of the $f_0(980)$ resonance. It is shown that the existence of two poles close to $K\bar{K}$ threshold, as found in many data fits and confirmed here, can be reconciled with the $K\bar{K}$ molecular origin of the $f_0(980)$. Due to a strong coupling between channels the number of the $S$-matrix poles close to the physical region in the physical case exceeds the number of bare states introduced in the model.