Five-flavor pentaquarks and other light- and heavy-flavor symmetry partners of the LHCb hidden-charm pentaquarks

The discovery of three pentaquark peaks — the Pc(4312), Pc(4440) and Pc(4457) — by the LHCb collaboration has a series of interesting consequences for hadron spectroscopy. If these hidden-charm objects are indeed hadronic molecules, as suspected, they will be constrained by heavy-flavor and SU(3)-flavor symmetries. The combination of these two symmetries will imply the existence of a series of five-flavor pentaquarks with quark content b¯csdu and bc¯sdu, that is, pentaquarks that contain each of the five quark flavors that hadronize. In addition, from SU(3)-flavor symmetry alone we expect the existence of light-flavor partners of the three Pc pentaquarks with strangeness S=−1 and S=−2. The resulting structure for the molecular pentaquarks is analogous to the light-baryon octet — we can label the pentaquarks as PQ′Q¯N, PQ′Q¯Λ, PQ′Q¯Σ, PQ′Q¯Ξ depending on their heavy- and light-quark content (with N, Λ, Σ, Ξ the member of the light-baryon octet to which the light-quark structure resembles and Q′, Q¯ the heavy quark-antiquark pair). In total we predict 45 new pentaquarks from heavy- and light-flavor symmetries alone, which extend up to 109 undiscovered states if we also consider heavy-quark spin symmetry. If an isoquartet (I=3/2) hidden-charm pentaquark is ever observed, this will in turn imply a second multiplet structure resembling the light-baryon decuplet: PQ′Q¯Δ, PQ′Q¯Σ⁎, PQ′Q¯Ξ⁎, PQ′Q¯Ω.