Relativistic quark spin coupling effects in the nucleon electromagnetic form factors

Abstract

We investigate the effect of different forms of relativistic spin coupling of constituent quarks in the nucleon electromagnetic form factors. The fourdimensional integrations in the two-loop Feynman diagram are reduced to the null-plane, such that the light-front wave function is introduced in the computation of the form factors. The neutron charge form factor is very sensitive to different choices of spin coupling schemes, once its magnetic moment is fitted to the experimental value. The scalar coupling between two quarks is preferred by the neutron data, when a reasonable fit of the proton magnetic momentum is found.

Nucleon magnetic moments in light-front models with quark mass asymmetries

“…From the point of view of the static electroweak observables, the value of p does not present an independent feature at least in the static observables, which are strongly correlated, as long as p > 2 [5,12]. Here p = 3 is chosen without any loss of generality in our analysis, as different momentum components of the wave function leads to the same correlation between the nucleon magnetic moments [5]. Furthermore, we will show that the two-scale power-law model also preserves the correlation curve between the magnetic moments.…”

“…The spin part of the nucleon light-front wave function is described with an effective Lagrangian for the N-q coupling, which is written as [5],…”

“…The matrix elements of the current J + N (q 2 ) are computed in the nucleon light-front spinor basis in the Breit-frame constrained by the Drell-Yan condition, which is written as [2,5]:…”

“…More recently, it was shown that in several nucleon light-front models, the proton and neutron magnetic moments are strongly correlated [5]. The detailed form of the correlation was found manly dependent on the relativistic spin coupling scheme.…”

“…In Ref. [5], the coupling of the quark to the nucleon fields was formulated through an effective Lagrangian, which dials the different relativistic spin coupling schemes. Although some of the previous calculations [2,3,4] were performed within the BakamjianThomas construction (BT) [6] of the nucleon light-front wave function, the results found for the magnetic moments were consistent with those obtained with an effective Lagrangian with mixed scalar plus gradient coupling [5].…”