Transversity distributions in the nucleon in the large-N_c limit

We compute the quark and antiquark transversity distributions in the nucleon at a low normalization point of 600 MeV in the large-$N_c$ limit, where the nucleon can be described as a soliton of an effective chiral theory (chiral quark-soliton model). The flavor-nonsinglet distributions, $\delta u(x) - \delta d(x)$ and $\delta\bar u(x) - \delta\bar d(x)$, appear in leading order of the $1/N_c$-expansion, while the flavor-singlet distributions, $\delta u(x) + \delta d(x)$ and $\delta\bar u(x) + \delta\bar d(x)$, are non-zero only in next-to-leading order. The transversity quark and antiquark distributions are found to be significantly different from the longitudinally polarized distributions $\Delta u (x) \pm \Delta d (x)$ and $\Delta\bar u (x) \pm \Delta\bar d (x)$, respectively, in contrast to the prediction of the naive non-relativistic quark model. We show that this affects the predictions for the spin asymmetries in Drell-Yan pair production in transversely polarized pp and ppbar collisions.Comment: 45 pages, 16 figure

Azimuthal asymmetries at CLAS: Extraction of e^a(x) and prediction of A_{UL}

First information on the chirally odd twist-3 proton distribution function e(x) is extracted from the azimuthal asymmetry, A_{LU}, in the electro-production of pions from deeply inelastic scattering of longitudinally polarized electrons off unpolarized protons, which has been recently measured by CLAS collaboration. Furthermore parameter-free predictions are made for azimuthal asymmetries, A_{UL}, from scattering of an unpolarized beam on a polarized proton target for CLAS kinematics.Comment: 9 pages, 5 figures, late

The chirally-odd twist-3 distribution function e(x) in the chiral quark-soliton model

The chirally-odd twist-3 nucleon distribution e(x) is studied in the large-Nc limit in the framework of the chiral quark-soliton model at a low normalization point of about 0.6 GeV. The remarkable result is that in the model e(x) contains a delta-function-type singularity at x=0. The regular part of e(x) is found to be sizeable at the low scale of the model and in qualitative agreement with bag model calculations.Comment: 16 pages, 6 figures, revtex, Ref.[50] and footnote 3 adde

Old and new parton distribution and fragmentation functions

A short review of problems with parton distribution functions in nucleons, non-polarized and polarized, is given. The main part is devoted to the transversity distribution its possible measurement and its first experimental probe via spin asymmetry in semi-inclusive DIS. It is argued that the proton transversity distribution could be successfully measured in future DIS experiments with {\it longitudinally} polarized target.Comment: 9 pages, latex, czjphys2.sty, 4 eps figures. Submitted at 35-th Rancontre de Moriond, March 2000 and at Praha-SPIN-2000, July 2000. To be published in Czechoslovak J. Phys. (Suppl) 51 (2001