Transverse force on quarks in deep-inelastic scattering

The interaction-dependent part of the x(2) moment of the twist-3 polarized parton distribution g(2)(x) is related to the transverse force acting on the active quark in deep-inelastic scattering off a transversely polarized nucleon immediately after it has absorbed the virtual photon. Similarly, the x(2) moment of the chirally odd twist-3 unpolarized parton distribution e(x) can be related to the transverse force experienced by a transversely polarized quark ejected from a transversely polarized nucleon.