Negative parity baryons in the $1/N_c$ expansion: the quark excitation versus the meson-nucleon resonance picture

Abstract

In order to better understand the fundamental issue regarding the compatibility between the quark-shell picture and that of resonances in meson-nucleon scattering in large $N_c$ QCD we extend the work of Cohen and Lebed on mixed symmetric $\ell$ = 1 baryons to analyze excited states with $\ell$ = 3. We give an explicit proof on the degeneracy of mass eigenvalues of a simple Hamiltonian including operators up to order $\mathcal{O}(N_c^0)$ \emph{i. e.} neglecting $1/N_c$ corrections in the quark-shell picture in the large $N_c$ limit. We obtain three degenerate multiplets formed of $\ell =3$ states, as in the case of $\ell$ = 1 baryons. The compatibility between this picture and that of resonances in meson-nucleon scattering is discussed in the light of the present results.

Comments: 18 pages, 4 tables. Published version. Note that Eqs. A1, A3 and A4 contain SO(3) Clebsch-Gordan coefficients, not Wigner 3j coefficients