  Parton distributions in impact parameter space, which are obtained by Fourier
transforming GPDs, exhibit a significant deviation from axial symmetry when
target and/or quark are transversely polarized. In combination with the final
state interactions, this transverse deformation provides a natural mechanism
for naive-T odd transverse single-spin asymmetries in semi-inclusive DIS. The
deformation of PDFs in impact parameter space can also be related to the
transverse force acting on the active quark in polarized DIS at higher twist.
