Single-spin Asymmetries in SIDIS Induced by Anomalous Quark-Gluon and Quark-Photon Couplings

We calculate the contribution of the nonperturbative Pauli couplings in the quark-photon and quark-gluon vertices to the single-spin asymmetries (SSAs) in semi-inclusive deep inelastic scattering (SIDIS). We describe the nucleon using the spectator model with scalar and axial-vector diquarks. Both of the new couplings can cause the helicity flip of the struck quark. The helicity flip and the rescattering induced by the nonperturbative gluon exchange between the struck quark and diquark lead to the SSAs. Their azimuthal dependencies are the same as that usually ascribed to the Collins and Sivers effects. Our numerical results, based on the instanton model for the QCD vacuum, show that the nonperturbative quark-gluon and quark-photon interactions have a strong influence on these asymmetries.