Nucleon spin content and axial coupling constants in QCD sum rules approach

Abstract

The review of current experimental situation in the measurements of the first moment ${\Gamma }_{p,n}$ of spin dependent nucleon structure functions $g_{1;p,n}(x,Q^2)$ is presented. The results of the calculations of twist-4 corrections to ${\Gamma }_{p,n}$ are discussed and their accuracy is estimated. The part of the proton spin $\Sigma$ carried by $u,d,s$ quarks is calculated in the framework of the QCD sum rules in the external fields. The operators up to dimension 9 are accounted. An important contribution comes from the operator of dimension 3, which in the limit of massless $u,d,s$ quarks is equal to the derivative of QCD topological susceptibility ${\chi }^{\prime }(0)$. The comparison with the experimental data on $\Sigma$ gives ${\chi }^{\prime }(0)=(2.3\pm 0.6)\times 10^{-3}Ge{V}^2$. The limits on $\Sigma$ and ${\chi }^{\prime }(0)$ are found from selfconsistency of the sum rule, $Σ\ga 0.05, χ' (0) \ga 1.6 \times 10^{-3} GeV^2$. The values of $g_A=1.37\pm 0.10$ and $g_A^8=0.65\pm 0.15$ are also determined from the corresponding sum rules.

Lecture at St.Petersburg Winter School on Theoretical Physics, Febr. 23-28, 1998 to be published in Proceedings, 14 pages, LaTeX 2e, 4 eps figures included using epsf.sty

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• Measurement of the Neutron Spin Structure Function $g_1^n$ with a Polarized ^3He Target
• Spin Structure of the Proton from Polarized Inclusive Deep-Inelastic Muon-Proton Scattering
• Next-to-Leading Order QCD Analysis of Polarized Deep Inelastic Scattering Data
• The (alpha_s)^3 approximation of Quantum Chromodynamics to the Ellis-Jaffe sum rule
• Vacuum expectations of the high dimensional operator and their contribution in Bjorken and Ellis-Jaffe sum rules

Cited by in corpus (4)

• Condensates in Quantum Chromodynamics
• In quest of "just" the Standard Model on D-branes at a singularity
• Type IIB orientifolds on Gepner points
• Axial Vector Current Matrix Elements and QCD Sum Rules