Novel pentaquark picture for singly heavy baryons from chiral symmetry

We propose a new type of structure for singly heavy baryons of Qqq (q) over barq in addition to the conventional one of Qqq. Based on chiral symmetry of the light quarks, we show that the Qqq (q) over barq baryon offers a novel picture for heavy-quark spin-singlet and flavor-antisymmetric baryons. By making use of the effective Lagrangian approach, we find that Lambda(c) (2765) and Xi(c) (2967) are mostly Qqq (q) over barq, while Lambda(c) (2286) and Xi(c) (2470) are mostly Qqq. The masses of negative-parity baryons are predicted. We also derive a sum rule and the extended Goldberger-Treiman relation that the masses of the baryons satisfy. Furthermore, a mass degeneracy of parity partners of the baryons with the restoration of chiral symmetry is discussed. These are the unique features that the conventional picture of radial excitation in the quark model does not accommodate. Our findings provide useful information not only for future experiments but also for future lattice simulations on diquarks.