Parton distribution functions from nonlocal light-cone operators with definite twist

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Abstract
We introduce the chiral-even and chiral-odd quark distributions as forward matrix elements of related bilocal quark operators with well-defined (geometric) twist. Thereby, we achieve a Lorentz invariant classification of these distributions which differ from the conventional ones by explicitly taking into account the necessary trace terms. The relations between both kinds of distribution functions are given and the mismatch between their different definition of twist is discussed. Wandzura-Wilczek--like relations between the conventional distributions (based on dynamical twist) are derived by means of geometric twist distribution functions.Comment: 17 pages, REVTEX, Extended version, The Introduction has been rewritten, Setion V "Wandzura-Wilczek--like relations" and App. B are added; Sign errors are correcte