Parton distribution functions from nonlocal light-cone operators with definite twist - art. no. 094003

We introduce the chiral-even and chiral-odd quark distributions as forward matrix elements of related bilocal quark operators with a well-defined (geo metric) twist. Thereby, we achieve a Lorentz invariant classification of th ese distributions which differ from the conventional ones by explicitly tak ing into account the necessary trace terms. The relations between both kind s of distribution functions are given and the mismatch between their differ ent definition of twist is discussed. Wandzura-Wilczek-like relations betwe en the conventional distributions (based on dynamical twist) are derived by means of geometric twist distribution functions.