Role of diquark correlations and the pion cloud in nucleon elastic form factors

Understand

Electromagnetic form factors of the nucleon in the space-like region are investigated within the framework of a covariant and confining Nambu-Jona-Lasinio model.

• The bound state amplitude of the nucleon is obtained as the solution of a relativistic Faddeev equation, where diquark correlations appear naturally as a consequence of the strong coupling in the colour $\bar{3}$ $qq$ channel.
• Pion degrees of freedom are included as a perturbation to the "quark-core" contribution obtained using the Poincar\'e covariant Faddeev amplitude.
• While no model parameters are fit to form factor data, excellent agreement is obtained with the empirical nucleon form factors (including the magnetic moments and radii) where pion loop corrections play a critical role for $Q^2 \lesssim 1\,$GeV$^2$.