Generalized SU(3) Nambu-Jona-Lasinio model. (II). From current to constituent quarks

We investigate the properties of constituent quarks, i.e. quarks dressed by their strong interactions, in a generalized Nambu-Jona-Lasinio model with N_f = 3 flavours. In the Hartree-Fock approximation, the step from structureless current quarks to massive constituent quarks is made through dynamical mass generation which implies spontaneous chiral symmetry breaking. We study, in particular, the quark scalar, vector and axial vector currents within this framework. We demonstrate that, at low energy and momentum transfers, single valence quarks are strongly screened by quark-antiquark polarization effects. For the electromagnetic currents, we recover relationships familiar from the vector meson dominance model. For the axial current, screening by J^π = 1⁺ quark-antiquark modes leads to an effective quark axial vector constant g_A < 1 which satisfies the Goldberger-Treiman relation at the quark level. The spin content of the proton is also discussed in this framework. We calculate quark magnetic moments and electromagnetic form factors and discuss their related sizes.