Pentaquark states from bound state approach with chiral partner structure

The observation of the two states $P_c(4380)$ and $P_c(4445)$ [Phys.Rev.Lett. 115 (2015) 072001] solids the existence of the pentaquark state in Nature. In this work, we study the spectrum of the pentaquark states including one or two heavy quarks based on the bound state approach by binding the heavy-light mesons to the nucleon as a soliton in an effective Lagrangian approach. By regarding the $H$ doublet and $G$ doublet as chiral partners to each other and coupling them to light mesons with a minimal derivative, the chiral partner structure of the pentaquark states is calculated. We find that the bound state approach prefers to arrange $P_c^+(4440)$ and $P_c(4457)$ into a heavy quark doublet $(\frac{1}{2}^-,\frac{3}{2}^-)$ so both decay to $J/\psi p$ through the $S$-wave. The predicted spectrum shown in this work serves as a guide for the experimental hunting of more pentaquark states.