arXiv subjects

A. Mirjalili

Publications and source records attributed to A. Mirjalili.

22 records · Page 2Linked to original sources

arXiv2003

Polarized parton distribution functions in the valon model framework, using QCD fits to Bernstein polynomials

In this paper polarized valon distribution is derived from unpolarized valon distribution. In driving polarized valon distribution some unknown parameters exist which must be determined by fitting to experimental data. Here we have used Bernstein polynomial method to fit QCD predictions for the moments of $g_1^p$ structure function, to suitably the constructed appropriate average quantities of the E143 and SMC experimental data. After calculating polarized valon distributions and all parton distributions in a valon, polarized parton density in a proton are available. The results are used to evaluate the spin components of proton. It turns out that the results of polarized structure function are in good agreement with all available experimental data on $g_{1}^p$ of proton.

hep-ph↗

arXiv2002

Direct extraction of QCD LambdaMSbar from moments of structure functions in neutrino-nucleon scattering, using the CORGI approach

We use recently calculated next-to-next-to-leading (NNLO) anomalous dimension coefficients for the n=1,3,5,...,13 moments of the xF3 structure function in nuN scattering, together with the corresponding three-loop Wilson coefficients, to obtain improved QCD predictions for the moments. The Complete Renormalization Group Improvement (CORGI) approach is used, in which all dependence on renormalization or factorization scales is avoided by a complete resummation of ultraviolet logarithms. The Bernstein Polynomial method is used to compare these QCD predictions to the xF3 data of the CCFR collaboration. Direct fits for LambdaMSbar(5), with Nf=5 effective quark flavours, over the range 20<Q^2<125.9 GeV^2 were performed. We obtain LambdaMSbar(5)=202+54/-45 MeV, corresponding to the three-loop running coupling alphas(MZ)=0.1174+0.0043-0.0043. Including target mass corrections as well we obtain LambdaMSbar(5)=228+35/-36 MeV, corresponding to alphas(MZ)=0.1196+0.0027-0.0031.

hep-ph↗

arXiv2001

Renormalon-inspired resummations for vector and scalar correlators- estimating the uncertainty in {alpha}_{s}({m}_τ^{2}) and and α({M}_{Z}^{2})

We perform an all-orders resummation of the QCD Adler D-function for the vector correlator, in which the portion of perturbative coefficients involving the leading power of b, the first beta-function coefficient, is resummed. To avoid a renormalization scale dependence when we match the resummation to the exactly known NLO and NNLO results, we employ the Complete Renormalization Group Improvement (CORGI) approach. These fixed-order and resummed CORGI results are analytically continued by numerically performing a contour integral to obtain corresponding fixed and all-orders ``contour-improved'' results for the e+e- R-ratio ands its tau decay analogue R_τ. The difference between these fixed-order and all-order results is used to estimate the uncertainty in the extraction of {alpha}_{s}({M}_{Z}^{2}} from R_τ measurements, and that in the QED coupling α({M}_{Z}^{2}) due to hadronic corrections related to R. Analogous resummations for the scalar correlator are performed, and used to assess the uncertainty in the Higgs decay width to a heavy quark pair. We point out that CORGI fixed-order contour-improved results for R and the Higgs decay width, can be given explicitly in terms of the Lambert-W function and hypergeometric functions, avoiding the need for numerical integration.

hep-ph↗

arXiv2000

Complete Renormalization Group Improvement-Avoiding Factorization and Renormalization Scale Dependence in QCD Predictions

For moments of leptoproduction structure functions we show that all dependence on the renormalization and factorization scales disappears, provided that all the ultraviolet logarithms involving the physical energy scale Q are completely resummed. The approach is closely related to Grunberg's method of Effective Charges. A direct and simple method for extracting the universal dimensional transmutation parameter of QCD from experimental data is advocated.

hep-ph↗