Bethe-Salpeterqqqdynamics: Electromagnetic properties of baryons

The Bethe-Salpeter model for $q\overline{q}$ and $\mathrm{qqq}$ systems under harmonic confinement, previously found to fit the $q\overline{q}$ and $\mathrm{qqq}$ mass spectra of light ($u$,$d$,$s$) quarks rather well with a universal spring constant ($\tilde{\omega }=0.15\mathrm{}$ GeV) and the concerned quark mass ($m_{\mathrm{ud}}=0.28\mathrm{}$ GeV, $m_s=0.35\mathrm{}$ 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 $q\overline{q}$ 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, ${\mu }_p=2.796\mathrm{} \mathrm{}\left(2.793\right)\mathrm{}$ nuclear magnetons and ${〈{r_p}^2〉}^{\frac{1}{2}}=0.86\mathrm{} \mathrm{}\left(0.87\right)\mathrm{}$ fm. The helicity amplitudes $A_{\frac{3}{2}}$ and $A_{\frac{1}{2}}$ for $\Delta \to N\gamma$ 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.