Nucleon to Delta electromagnetic transition in the Dyson-Schwinger approach

We study the N-Delta-gamma transition in the Dyson-Schwinger approach. The nucleon and Delta baryons are treated as quark-diquark bound states, where the ingredients of the electromagnetic transition current are computed self-consistently from the underlying dynamics in QCD. Although our approach does not include pion-cloud effects, we find that the electric and Coulomb quadrupole form-factor ratios R_EM and R_SM show good agreement with experimental data. This implies that the deformation from a spherical charge distribution inside both baryons can be traced back to the appearance of p waves in the nucleon and Delta bound-state amplitudes which are a consequence of Poincare covariance. On the other hand, the dominant transition amplitude, i.e. the magnetic dipole transition form factor, underestimates the data by ~25% in the static limit whereas agreement is achieved at larger momentum transfer, which is consistent with missing pion-cloud contributions. We furthermore find that the static properties of the form factors are not very sensitive to a variation of the current-quark mass.Comment: 21 pages, 9 figures, 4 tables. Added reference

Theory introduction to baryon spectroscopy

In these introductory notes I give a brief overview on some theoretical aspects of light baryon spectroscopy. The first part contains a discussion of the symmetries of the baryon spectrum, the construction of flavor wave functions and some basic features of quark models. The second part examines the need for relativistic quantum field theory and focusses on spectrum calculations with functional methods.Comment: 20 pages, 11 figures, 1 table. Contribution to the 2021 School on the Physics of Baryons, Oct 18-22 2021, Sevill