| Abstract: | If the number of colors Nc is taken large, baryons and their excitations can be considered in a mean-field approach. We argue that the mean field in baryons breaks spontaneously the spherical and SU(3) flavor symmetries, but retains the SU(2) symmetry of simultaneous rotations in space and isospace. The one-quark and quark-hole excitations in the mean field, together with the SU(3) rotational bands about them determine the spectrum of baryon resonances, which turns out to be in good accordance with reality when one puts Nc = 3. A by-product of this scheme is a confirmation of the light pentaquark Θ+ baryon uudd(s) as a typical Gamov-Teller resonance long known in nuclear physics. An extension of the same large-Nc logic to charmed baryons leads to a prediction of a anti-decapenta (15)-plet of charmed pentaquarks, two of which, B+c+ = cuud-s and B+c = cudd(s), may be light and stable with respect to strong decays. |
