SU(6) breaking effects in the nucleon elastic electromagnetic form factors

The effects of both kinematical and dynamical SU(6) breakings on the nucleon elastic form factors, G(E)(N)(Q(2)) and G(M)(N) (Q(2)), are investigated within the constituent quark model formulated on the light-front. The investigation is focused on G(E)(n)(Q(2)) and the ratio G(M)(p) (Q(2))/G(M)(n) (Q(2)), which within the SU(6) symmetry are given by G(E)(n) (Q(2)) = 0 and G(M)(p)(Q(2))/G(M)(n) (Q(2)) = -3/2, respectively. It is shown that the kinematical SU(6) breaking caused by the Melosh rotations of the quark spins as well as the dynamical breaking due to the mixed-symmetry component generated in the nucleon wave function by the spin-dependent interaction among quarks, sharply affect both G(E)(n) (Q(2)) and G(M)(p) (Q(2))/G(M)(n) (Q(2)). The calculated G(E)(n) (Q(2)) is found to be qualitatively consistent with existing data, though only similar or equal to 65% of the experimental neutron charge radius can be explained without invoking effects from possible finite size of the constituent quarks and/or many-body currents. At the same time the predictions for the magnetic ratio G(M)(p) (Q(2))/G(M)(n) (Q(2)) turn out to be inconsistent with the data. It is however shown that the calculations of G(M)(N) (Q(2)) based on different components of the one-body electromagnetic current lead to quite different results. In particular, the calculations based on the plus component are found to be plagued by spurious effects related to violations of the angular condition. These unwanted effects can be avoided by considering the transverse y-component of the current. In this way our final predictions are consistent with the data on both G(E)(n) (Q(2)) and G(M)(p) (Q(2))/G(M)(n) (Q(2)).