Strange pentaquark molecules in QCD sum rules

Abstract

We study hidden- and open-strange pentaquark configurations in the hadronic molecular picture with QCD sum rules. Starting from the baryon octet combined with an $s\bar{s}$ pair, we construct 21 interpolating currents with $J=1/2$ and $3/2$. In the analysis, contributions up to dimension 11 are included in the operator product expansion, and both parity-projected spectra and the chiral-even and chiral-odd Lorentz structures are examined. No bound-state solution is found in the $J^P=1/2^{-}$ sector, although several channels generate resonance masses near nearby thresholds or poorly established strange baryons. In the $J^P=3/2^{-}$ sector, the $\Sigma \varphi$ and $\Xi K^{\ast }$ currents both support a near-threshold bound-state solution around $2.2$ GeV, suggesting a possible molecular configuration with channel mixing. In contrast, positive-parity sectors are more difficult to identify the corresponding states. In addition, our results favor the spin-parity assignments $J^P=3/2^{-}$ for $\Sigma (2250)$, $J^P=1/2^{-}$ for $\Sigma (2455)$, $\Sigma (2620)$, and $\Xi (2370)$, and $J^P=3/2^{+}$ for $\Xi (2250)$. These results provide a systematic QCD sum rule study of strange pentaquark molecular candidates in the strange sector.