Abstract :
Relations between nucleon, Δ and nucleon–Δ electromagnetic properties associated with chiral physics which have been derived in a pure large-Nc limit are greatly modified in a combined large Nc and chiral limits; the large Nc relations are valid for (MΔ−MN)/mπ⪡1. The E2/M1 ratio for the nucleon–Δ transition is shown to scale as ϵ−1 (with ϵ∼1/Nc, ϵ∼mπ/Λ with Λ a typical hadronic scale) in the combined large Nc and chiral expansions as opposed to Nc−2 in the pure large Nc expansion.
