The Sivers mechanism for the single-spin asymmetry in unpolarized lepton scattering from a transversely polarized nucleon is driven by the orbital angular momentum carried by its quark and gluon constituents, combined with QCD final-state interactions. Both quark and gluon mechanisms can generate such a single-spin asymmetry, though only the quark mechanism can explain the small single-spin asy...

We study the role of the nucleon resonances (N *) in ω photoproduction by using the quark model resonance parameters predicted by Capstick and Roberts. The employed γN → N * and N * → ωN amplitudes include the configuration mixing effects due to the residual quark-quark interactions. The contributions from the nucleon resonances are found to be important in the differential cross sections at la...

A dynamical approach is developed to predict the πN scattering amplitudes starting with the constituent quark models. The first step is to apply a variational method to solve the three-quark bound state problem. The resulting wave functions are used to calculate the N → πN, ηN, π∆ vertex functions by assuming that the π and η mesons couple directly to quarks. These vertex functions and the pred...

The quark helicity measured in polarized deep inelastic scattering is different from the quark spin in the rest frame of the nucleon. We point out that the quark spin distributions ∆qRF (x) are connected with the quark helicity distributions ∆q(x) and the quark transversity distributions δq(x) by an approximate relation: ∆qRF (x) +∆q(x) = 2δq(x). This relation will be useful in order to measure...

We consider the leading twist T -odd contributions as the dominant source of the azimuthal and transverse single spin asymmetries in SIDIS and dilepton production in Drell-Yan Scattering. These asymmetries contain information on the distribution of quark transverse spin in (un)polarized protons. In the spectator framework we estimate these asymmetries at HERMES kinematics and at 50 GeV for the ...