Pion photoproduction amplitude relations in the1/Ncexpansion

Abstract

We derive expressions for pion photoproduction amplitudes in the 1/N c expansion of QCD, and obtain linear relations directly from this expansion that relate electromagnetic multipole amplitudes at all energies. The leading-order relations in 1/N c compare favorably with available data, while the next-to-leading order relations seem to provide only a small improvement. However, when resonance parameters are compared directly, the agreement at O(1/N c ) or O(1/N 2 c ) is impressive.

Pion electroproduction amplitude relations in the1/Ncexpansion

“…[23]; the differences are particularly noted. The results for either process are obtained by starting with general meson-baryon scattering processes of the form…”

“…In this paper we modify the approach for describing meson-baryon scattering amplitudes in the 1/N c expansion, as it was applied to the case of pion photoproduction γN → πN [23], to provide a model-independent expansion for electromagnetic multipole amplitudes of the related pion electroproduction process e − N → e − πN , which at its essence is the virtual photon process γ * N → πN . Studies of γN → πN using the more traditional "operator" approach to large N c baryons also appear in the literature [24].…”

Excited Baryons in Large Nc QCD

“…For example one can work at next to leading order (which only has additional predictive power in the reaction πN → π∆) [ 2] or study ηN scattering, photoprodction reactions [ 6] or scattering in exotic (pentaquark) channels [ 4].…”

“…This talk discusses some recent developments in the description of excited baryons via large N c QCD [ 1,4,2,3,5,6]. The work discussed was principally done in collaboration with Rich Lebed of ASU; two students of mine, Abhi Nellore and Dan Dakin also made substantial contributions and Dan Martin, a student of Rich Lebed's, also contributed.…”

πN→multi-πNscattering in the1/Ncexpansion

“…1 Recent development of the original scattering formalism [2][3][4][5][6][7][8] can be reviewed in Refs. 9 The central idea rests upon symmetries that emerge for QCD in the large N c limit.…”