Speaker
Description
We review the recent experimental and theoretical
advances in the study of the electromagnetic
structure of baryons and transitions between baryon states.
The main focus is in the study of the
$\gamma^\ast N \to N^\ast$ transition amplitudes and multipole form
factors in terms of the squared momentum transfer $Q^2$.
The status of the states $\Delta(1232)\frac{3}{2}^+$,
$N(1440)\frac{1}{2}^+$, $N(1520)\frac{3}{2}^-$ and $N(1535)\frac{1}{2}^-$
is discussed in detail, but higher mass $N^\ast$ states
are also mentioned.
The results are interpreted using theoretical models
based on quark degrees of freedom, meson cloud excitations
of baryon cores, and others.
We also look for the analytic structure
of the helicity transition amplitudes and multipole form
factors in terms of the $N^\ast$ spin.
We will emphasize both the low-$Q^2$ and large-$Q^2$
regions to reinforce crucial physical constraints on observables that
hold in these limits.
