Nucleon resonances N(1875) and N(2100) as strange partners of the LHCb pentaquarks

In this work, we investigate the possibility of interpreting two nucleon resonances, the N(1875) and the N(2100), as hadronic molecular states from the Sigma*K and Sigma K* interactions, respectively. With the help of effective Lagrangians in which coupling constants are determined by the SU( 3) symmetry, the Sigma*K and Sigma K* interactions are described by the vector-meson and pseudoscalar-meson exchanges. With the one-boson-exchange potential obtained, bound states from the Sigma*K and Sigma K* interactions are searched for in a quasipotential Bethe-Saltpeter equation approach. A bound state with quantum number I(J(P)) = 1/2(3/2(-)) is produced from the Sigma*K interaction, which can be identified as the N(1875) listed in PDG. It can be seen as a strange partner of the LHCb pentaquark P-c(4380) with the same quantum numbers in the molecular state picture. The Sigma K* interaction also produces a bound state with quantum number I(J(P)) 1/2(3/2(-)), which is related to experimentally observed N(2100) in the phi photo-production. Our results suggest that the N(2120) observed in the K Lambda(1520) photoproduction and the N(2100) observed in the. photoproduction have different origins. The former is a conventional threequark state while the latter is a Sigma K* molecular state, which can be seen as a strange partner of the P-c(4450) with different spin parity.