We calculate the electromagnetic moments and radii of the ∆(1232) in the nonrelativistic quark model, including two-body exchange currents. We show that two-body exchange currents lead to nonvanishing ∆ and N → ∆ transition quadrupole moments even if the wave functions have no D-state admixture. The usual explanation based on the single-quark transition model involves D-state admixtures but no exchange currents. We derive a parameter-free relation between the N → ∆ transition quadrupole moment and the neutron charge radius, namely Q N →∆ = 1 √ 2 r 2 n . Furthermore, we calculate the M 1 and E2 amplitudes for the process γ + N → ∆. We find that the E2 amplitude receives sizeable contributions from exchange currents. These are more important than the ones which result from D-state admixtures due to tensor forces between quarks if a reasonable quark core radius of about 0.6 fm is used. We obtain a ratio of E2/M 1 = −3.5%. * In this work we use r q = 0.4 fm (see eq. (9)). † For recent reviews of the CQM see ref. [25].

We discuss the dressing of constituent quarks with a pseudoscalar meson cloud within the effective chiral quark model. SU (3) f symmetry breaking effects are included explicitly. Our results are compared with those of the traditional meson cloud approach in which pions are coupled to the nucleon. The pionic dressing of the constituent quarks explains the experimentally observed violation of the Gottfried Sum Rule and leads to an enhanced nonperturbative sea of qq pairs in the constituent quark and consequently in the nucleon. We find 2.5 times more pions and 10-15 times more kaons in the nucleon than in the traditional picture. Thed −ū asymmetry obtained here is concentrated at somewhat smaller x and theū/d ratio is somewhat different than in the traditional meson cloud model of the nucleon.

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We address the question of the intrinsic quadrupole moment Q 0 of the nucleon in various models. All models give a positive intrinsic quadrupole moment for the proton. This corresponds to a prolate deformation. We also calculate the intrinsic quadrupole moment of the ∆(1232). All our models lead to a negative intrinsic quadrupole moment of the ∆ + corresponding to an oblate deformation.

We calculate expressions for the quadrupole moments of nonstrange baryons in which the number of QCD color charges is N c . Using only the assumption of single-photon exchange, we obtain 4 relations among the 6 moments, and show how all of them may be obtained from Q ∆ + p up to O(1/N 2 c ) corrections. We compare to the N c = 3 case, and obtain relations between the neutron charge radius and quadrupole moments. We also discuss prospects for the measurement of these moments.