How does the S11 N*(890) state emerge from a naive K-matrix fit?

Yao Ma,Wen-Qi Niu,Yu-Fei Wang,Han-Qing Zheng

Figure 3. Different estimations on the spectral function of left-hand integral: the solid (blue) line depicts the $\chi {PT}$ result at $O({p}^{3})$ [3]; the dotted straight line (orange) is from Fit I; dotted-dashed (green) line is from Fit II; dashed (green) line is generated by Fit III. Small fluctuations in these curves are either from nearby (spurious) singularities or from numerical instabilities and should be ignored.