Narrow Results

We report a study on the non-pertribative structure of the polarized nucleon sea using the meson cloud model. It is found that the SU(2) flavour symmetry and strange-antistrange symmetry in the polarized nucleon sea are broken. Our calculations are in agreement with the recent results from HERMES Collaboration.

We present a general representation for the nucleon distribution amplitudes and for the nucleon to pion transition distribution amplitudes in terms of light-cone wave functions. We apply our formalism to a light-cone constituent quark model giving some numerical results for both the classes of observables.

A constituent quark model based on the spectator formalism is applied to the γN → N* transition for the three cases, where N* is the nucleon, the Δ and the Roper resonance. The model is covariant, and therefore can be used for the predictions at higher four-momentum transfer squared, Q². The baryons are described as an off-mass-shell quark and a spectator on-mass-shell diquark systems. The quark electromagnetic current is described by quark form factors, which have a form inspired by the vector meson dominance. The valence quark contributions of the model are calibrated by lattice QCD simulations and experimental data. Contributions of the meson cloud to the inelastic processes are explicitly included.