Bethe-Salpeter qqq dynamics: electromagnetic properties of baryons

Abstract

The Bethe-Salpeter model for qq̅ and qqq systems under harmonic confinement, previously found to fit the qq̅ and qqq mass spectra of light (u,d,s) quarks rather well with a universal spring constant (ω = 0.15 GeV) and the concerned quark mass (m_ud = 0.28 GeV, m_s = 0.35 GeV) is employed to predict some crucial electromagnetic properties of baryons as a generalization of a similar method recently developed for the electromagnetic interaction of qq̅ mesons. The major successes, in which the relativistic features of the model have played a crucial role, are in respect of magnetic moments of baryons and the charge radius of the proton, all in very good agreement with experiment with no free parameters. In particular, μ_p=2.796 (2.793) nuclear magnetons and <r_p²>^1/2=0.86 (0.87) fm. The helicity amplitudes A_3/2 and A_1/2 for Δ→Nγ also reveal an improved fit to data over previous quark-model calculations. The significance of these results is discussed in relation to contemporary confinement models.