Baryon magnetic moments in alternate1/Ncexpansions

Abstract

Recent work shows not only the necessity of a 1/N c expansion to explain the observed mass spectrum of the lightest baryons, but also that at least two distinct large N c expansions, in which quarks transform under either the color fundamental or the two-index antisymmetric representation of SU(N c ), work comparably well. Here we show that the baryon magnetic moments do not support this ambivalence; they strongly prefer the color-fundamental 1/N c expansion, providing experimental evidence that nature decisively distinguishes among 1/N c expansions for this observable.

Octet to decuplet electromagnetic transition in a relativistic quark model

“…Our results for the decay widths in Table VII are comparable with most of the predictions presented in the literature [11][12][13][14][15]17,[20][21][22][23][24]27,65]. The exception is the result for the Á !…”

“…Ã decay width are in the range 150-300 keV for a large variety of quark models, algebraic models of hadron structure, Skyrme, and soliton models [11][12][13][14][15]17,[20][21][22]. Only HB PT has a window 252-540 keV [24], while the large N c limit predicts 336 AE 81 keV [27] and may overestimate the result of 300 keV, as well as the QCD sum rules with 409 keV [23]. Our result, 284 keV, underestimates the experimental value from Ref.…”

“…The exception is the result for the Á ! N reaction, where most of the models underestimate the experimental data by more than 200 keV [11,14,15,17,21,22,28], except for the heavy baryon chiral perturbation theory (HB PT) [24], large N c limit [27], and QCD sum rules [23].…”

“…AE þ decay width, most of the predictions are in the range 50-110 keV, with the following exceptions: QCD sum rules (150 keV) [23], an algebraic model of hadron structure (141 keV) [28], HB PT (70-220 keV) [24], and large N c limit (140 AE 36 keV) [27]. Overall, these estimates are considerably smaller than the experimental result of 250 AE 70 keV [5], except for HB PT [24].…”

“…[4][5][6][7][8].) In the past, several theoretical studies of the octet to decuplet electromagnetic transitions were performed in nonrelativistic and relativistic quark models [9][10][11][12][13][14][15][16][17][18][19], Skyrme and soliton models [20][21][22], QCD sum rules [23], chiral perturbation theory [24][25][26], large N c limit [27], algebraic models of hadron structure [28], and lattice QCD [29]. In particular, lattice QCD studies for the à N !…”