On Combining High and Low Q**2 Information on the Polarized Parton Densities

We draw attention to some problems in the combined use of high-Q^2 deep inelastic scattering (DIS) data and low-Q^2 hyperon \beta-decay data in the determination of the polarized parton densities. We explain why factorization schemes like the JET or AB schemes are the simplest in which to study the implications of the DIS parton densities for the physics of the low-Q^2 region.Comment: 10 pages, LaTeX, minor corrections made in Section 4, a reference added, to be published in JHE

Constraints on "Second Order Fixed Point" QCD from the CCFR Data on Deep Inelastic Neutrino-Nucleon Scattering

The results of LO {\it Fixed point} QCD (FP-QCD) analysis of the CCFR data for the nucleon structure function $~xF_3(x,Q^2)~$ are presented. The predictions of FP-QCD, in which the Callan-Symanzik $~\beta~$ function admits a {\it second order} ultraviolet zero at $~\alpha = \alpha_0~$ are in good agreement with the data. Constraints for the possible values of the $~\beta~$ function parameter $~b~$ regulating how fast $~\alpha_ s(Q^2)~$ tends to its asymptotic value $~\alpha_{0}\ne 0~$ are found from the data. The corresponding values of $~\alpha_{0}~$ are also determined. Having in mind our recent " First order fixed point" QCD fit to the same data we conclude that in spite of the high precision and the large $~(x,Q^2)~$ kinematic range of the CCFR data they cannot discriminate between QCD and FP-QCD predictions for $~xF_3(x,Q^2)~$.Comment: 8 pages, LaTe

New analysis concerning the strange quark polarization puzzle

The fact that analyses of semi-inclusive deep inelastic scattering suggest that the polarized strange quark density $\Delta s(x) + \Delta \bar{s}(x)$ is positive in the measured region of Bjorken x, whereas all analyses of inclusive deep inelastic scattering yield significantly negative values of this quantity, is known as the "strange quark polarization puzzle". We have analyzed the world data on inclusive deep inelastic scattering, including the COMPASS 2010 proton data on the spin asymmetries, and for the first time, the new extremely precise JLab CLAS data on the proton and deuteron spin structure functions. Despite allowing in our parametrization, for a possible sign change, our results confirm that the inclusive data yield significantly negative values for the polarized strange quark density.Comment: 8 pages, 3 figures, 3 tables; misprints for the values of $\chi^2/DOF$ in page 5 correcte

The Role of Higher Twist in Determining Polarized Parton Densities from DIS data

Different methods to extract the polarized parton densities from the world polarized DIS data are considered. The higher twist corrections $h^N(x)/Q^2$ to the spin dependent proton and neutron $g_1$ structure functions are found to be non-negligible and important in the QCD analysis of the present experimental data. Their role in determining the polarized parton densities in the framework of the different approaches is discussed.Comment: To appear in the Proceedings of the Spin2004 Symposium, Trieste, 11-16 Oct 200

Higher Twist Effects in Polarized DIS

The size of higher twist corrections to the spin proton and neutron g1 structure functions and their role in determining the polarized parton densities in the nucleon is discussed.Comment: 6 pages, 2 figures, to appear in the proceedings of First Workshop on Quark-Hadron Duality and the Transition to pQCD, Frascati, June 6-8, 200

Polarized Parton Densities in the Nucleon

We present a new NLO QCD analysis of the world data on inclusive polarized deep inelastic scattering. Comparing to our previous analysis: i) the values of g_A and a_8=3F-D are updated ii) the MRST'99 instead of the MRST'98 parametrization for the input unpolarized parton densities is used and iii) the recent SLAC E155 proton data on the spin asymmetry A1 are included in the analysis. A new set of polarized parton densities is extracted from the data and the sensitivity of the results to different positivity constraints is discussed.Comment: 4 pages, 1 figure, LaTeX, typing errors in the numbers for \Delta \Sigma are corrected, talk presented at the 9th International Workshop on Deep Inelastic Scattering and QCD (DIS2001), Bologna, Italy, 27 Apr-1 May 200