The Skyrmion strikes back: baryons and a new large Nc limit

In the large Nc limit of QCD, baryons can be modeled as solitons, for instance, as Skyrmions. This modeling has been justified by Witten's demonstration that all properties of baryons and mesons scale with Nc-1/2 in the same way as the analogous meson-based soliton model scales with a generic meson-meson coupling constant g. An alternative large Nc limit (the orientifold large Nc limit) has recently been proposed in which quarks transform in the two-index antisymmetric representation of SU(Nc). By carrying out the analog of Witten's analysis for the new orientifold large Nc limit, we show that baryons and solitons can also be identified in the orientifold large Nc limit. However, in the orientifold large Nc limit, the interaction amplitudes and matrix elements scale with Nc-1 in the same way as soliton models scale with the generic meson coupling constant g rather than as Nc-1/2 as in the traditional large Nc limit