arXiv subjects
Publications and source records attributed to Thomas D. COhen.
This talk reviews recent developments in the use of large $N_c$ QCD in the description of baryonic resonances. The emphasis is on the model-independent nature of the approach. Key issues discussed include the spin-flavor symmetry which emerges at large $N_c$ and the direct use of scattering observables. The connection to quark model approaches is stressed.
Relations between nucleon, $Δ$ and nucleon-$Δ$ electromagnetic properties associated with chiral physics which have been derived in a pure large-$N_c$ limit are greatly modified in a combined large $N_c$ and chiral limits; the large $N_c$ relations are valid for $(M_Δ-M_N)/m_π<<1$. The E2/M1 ratio for the nucleon-$Δ$ transition is shown to scale as $ε^{-1}$ (with $ε\sim 1/N_c$, $ε\sim m_π/Λ$ with $Λ$ a typical hadronic scale) in the combined large $N_c$ and chiral expansions as opposed to $N_c^{-2}$ in the pure large $N_c$ expansion.