ELECTROMAGNETIC PROPERTIES OF THE PION AS A COMPOSITE NAMBU-GOLDSTONE BOSON

Motivated by the Nambu-Jona-Lasinio model of light mesons, we introduce a covariant separable interaction to model the structure of relativistic quark-antiquark systems. The Schwinger-Dyson equation for the quark self-energy is solved analytically, generating a dynamical quark mass through spontaneous breaking of chiral symmetry, and yielding a pion which has zero mass in the chiral limit. The Bethe-Salpeter vertex function for this qqBAR pion, which has a momentum distribution and composite structure associated with the interaction, is obtained analytically. Using this vertex function, and a similar one for the rho meson, we calculate the electromagnetic observables of this composite Nambu-Goldstone boson, including effects from rho-meson dominance processes. Our calculation takes the composite structure of the mesons into account. The rho-meson effects are found to be very small in the pion charge form factor, but substantial in the charge radius. Using the model, predictions are made for gamma(*)pi(0) --> gamma and rho-pi-gamma transition form factors.