Spin Orbit Correlations

I discuss the physical interpretation for generalized parton distributions (GPDs) with special focus on those GPDs that describe parton asymmetries in impact parameter space. The chirally even GPD $E(x,0,-{\bf \Delta}_\perp^2)$ describes the transverse deformation of the distribution of unpolarized quarks in a transversely polarized nucleon. In combination with an attractive final state interaction (FSI) this deformation can explain the Sivers effect in SIDIS. The chirally odd GPD $\bar{E}_T(x,0,-{\bf \Delta}_\perp^2)$ describes the deformation of the distribution of transversely polarized quarks in an unpolarized target. I will explain the physics associated with the sign of $\bar{E}_T$ and its implications for measurements of the Boer-Mulders function.