Recent developments in nucleon spin structure with focus on h1L#perpendicular# and pretzelosity h1Tperpendicular

The leading twist transverse momentum dependent parton distribution functions h1L#perpendicular# and h1Tperpendicular, which is sometimes called ''pretzelosity,'' are studied. For h1L#perpendicular# we consider a ''Wandzura-Wilczek-type'' approximation, which follows from QCD equations of motion upon the neglect of pure twist-3 terms and allows to express it in terms of transversity. On the basis of available data from HERMES we test the practical usefulness of this approximation and discuss how it can be further tested by future CLAS and COMPASS data. We review the theoretical properties of pretzelosity and observe an interesting relation valid in a large class of relativistic models: The difference between helicity and transversity distributions, which is often said to be a 'measure of relativistic effects' in the nucleon, is nothing but the transverse moment of pretzelosity.