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

On a Possibility to Determine the Sign of the Polarized Gluon Distribution

We investigate the possibility to draw conclusions on the sign of the spin-dependent gluon distribution, $\Delta G(x, Q^2)$, from existing polarized DIS data. The spin-dependent parton distributions $\Delta u_v, \Delta d_v, \Delta {\bar u}, \Delta {\bar d}, \Delta {s}$, and $\Delta G$ are constructed in the framework of a phenomenological procedure taking into account some assumptions on signs of valence and sea parton distributions motivated by 't Hooft's mechanism of quark-quark interaction induced by instantons. The axial gluon anomaly and data on integral quark contributions to the proton spin, $\Delta \tilde u, \Delta \tilde d$, and $\Delta \tilde s$, are also taken into account. Predictions for the $x$- and $Q^2$-dependencies of the polarized proton and neutron structure functions, $g_1^p$ and $g_1^n$, are compared to experimental data. It is shown that the neutron structure function, $g_1^n$, is especially sensitive to the sign of $\Delta G(x, Q^2)$. The results of our analysis supports the conclusion that this sign should be positive.Comment: 14 pages, latex, 12 figure

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