Doubly-strange hidden-charm pentaquarks from the Fermi statistics of the light-quark cloud

Abstract

We extend the baryo-charmonium picture of pentaquarks -- a color-octet $c\bar c$ core bonded to a color-octet light-quark cloud -- to the doubly-strange sector $c\bar c ssq$. The mass splittings are set entirely by the light cloud, so the only new inputs are the strange-strange couplings $J^{ss}$, fixed by a second application of the chromomagnetic scaling, and an additive strange-mass increment taken from the observed $P_c\!\to\!P_{cs}$ shift. We obtain two negative-parity triplets, one produced with a kaon and one with an antiproton, the lowest kaon-associated $\tfrac12^-$ state near $4.60$~GeV and the antiproton-associated triplet some $120$~MeV below. The robust, distinctive prediction is that the upper two kaon-associated states form a near-degenerate doublet, in sharp contrast to the well-separated triplets of the lighter sectors -- a sparse, fixed-spacing pattern that sets the scheme apart from the molecular and diquark alternatives. The internal splittings follow without adjustment from the measured $P_c$ and $P_{cs}$ spectra; the absolute scale relies on the additive strange-mass ansatz, the main assumption of the extrapolation. The predicted masses agree with recent molecular coupled-channel and QCD sum-rule results.