471 research outputs found
NNLO QCD contributions to the flavor non-singlet sector of
We present the results of our QCD analysis for nonsinglet unpolarized quark
distributions and structure function . New parameterizations are
derived for the nonsinglet quark distributions for the kinematic wide range of
and . The analysis is based on the Jacobi polynomials expansion of the
structure function. The higher twist contributions of proton and deuteron
structure function are obtained in the large region. Our calculations for
nonsinglet unpolarized quark distribution functions based on the Jacobi
polynomials method are in good agreement with the other theoretical models. The
values of and are determined.Comment: 29 pages, 8 figure
Fixation of theoretical ambiguities in the improved fits to CCFR data at the next-to-next-to-leading order and beyond
Using the results for the NNLO QCD corrections to anomalous dimensions of odd
Mellin moments and NLO corrections to their coefficient functions we
improve our previous analysis of the CCFR'97 data for . The possibility
of extracting from the fits of -corrections is analysed using three
independent models,including infrared renormalon one. Theoretical quetion of
applicability of the renormalon-type inspired large- approximation for
estimating corrections to the coefficient functions of odd and even
non-singlet moments are considered. The comparison with [1/1] Pad\'e
estimates is given. The obtained NLO and NNLO values of are
supporting the results of our less definite previous analysis and are in
agreement with the world average value . We also
present first NLO extraction of . The interplay between
higher-order perturbative QCD corrections and -terms is demonstrated.
The results of our studies are compared with those obtained recently using the
NNLO model of the kernel of DGLAP equation and with the results of the NNLO
fits to CCFR'97 data, performed by the Bernstein polynomial technique.Comment: The errors in the coefficients of
(^3\Lambda_{\bar{MS}}^{(4)}$ in
Tables 6,11,12 by 3 MeV only (details are in the enclosed Erratum (in press)
Application of new multiloop QCD input to the analysis of data
The new theoretical input to the analysis of the experimental data of the
CCFR collaboration for structure function of deep inelastic
scattering is considered. This input comes from the next-to-next-to-leading
order corrections to the anomalous dimensions of the Mellin moments of the
structure function. The QCD scale is
extracted from higher-twist independent fits. The results obtained demonstrate
the minimization of the influence of perturbative QCD contributions to the
value of Comment: 7 pages, Based on contributions to Proceedings of Quarks-2000 Int.
Seminar, Pushkin, May 2000, Russia and ACAT'2000 Workshop, Fermilab, October
2000, USA; definite shortcomings are eliminated, resulys unchange
Scale Setting Using the Extended Renormalization Group and the Principle of Maximum Conformality: the QCD Coupling Constant at Four Loops
A key problem in making precise perturbative QCD predictions is to set the
proper renormalization scale of the running coupling. The extended
renormalization group equations, which express the invariance of physical
observables under both the renormalization scale- and scheme-parameter
transformations, provide a convenient way for estimating the scale- and
scheme-dependence of the physical process. In this paper, we present a solution
for the scale-equation of the extended renormalization group equations at the
four-loop level. Using the principle of maximum conformality (PMC) /
Brodsky-Lepage-Mackenzie (BLM) scale-setting method, all non-conformal
terms in the perturbative expansion series can be summed into the
running coupling, and the resulting scale-fixed predictions are independent of
the renormalization scheme. Different schemes lead to different effective
PMC/BLM scales, but the final results are scheme independent. Conversely, from
the requirement of scheme independence, one not only can obtain
scheme-independent commensurate scale relations among different observables,
but also determine the scale displacements among the PMC/BLM scales which are
derived under different schemes. In principle, the PMC/BLM scales can be fixed
order-by-order, and as a useful reference, we present a systematic and
scheme-independent procedure for setting PMC/BLM scales up to NNLO. An explicit
application for determining the scale setting of up to four
loops is presented. By using the world average , we obtain the asymptotic scale for the 't Hooft associated
with the scheme, MeV, and
the asymptotic scale for the conventional scheme,
MeV.Comment: 9 pages, no figures. The formulas in the Appendix are correcte
Next-to-next-to-leading order fits to CCFR'97 data and infrared renormalons
We briefly summarize the outcomes of our recent improved fits to the
experimental data of CCFR collaboration for structure function of deep-inelastic scattering at the next-to-next-to-leading order. Special
attention is paid to the extraction of and the parameter of the
infrared renormalon model for -correction at different orders of
perturbation theory. The results can be of interest for planning similar
studies using possible future data of Neutrino Factories.Comment: 3 pages, presented at WG3 of 4th NuFact'02 Workshop, London 1-6 July,
200
The order and corrections to the decay width of the neutral Higgs boson to the pair
We present the analytical expressions for the contributions of the order
and corrections to the
decay width of the Standard Model Higgs boson into the -pair. The
numerical value of the mixed QED and QCD correction of order
is comparable with the previously calculated
terms in the perturbative series for .Comment: LaTeX 5 pages, accepted for publication in Pisma Zh. Eksp. Teor. Fiz.
v 66, N5 (1997
The Generalized Crewther Relation in QCD and its Experimental Consequences
We use the BLM scale-fixing prescription to derive a renormalization-scheme
invariant relation between the coefficient function for the Bjorken sum rule
for polarized deep inelastic scattering and the -ratio for the
annihilation cross section. This relation provides a generalization of the
Crewther relation to non-conformally invariant gauge theories. The derived
relations allow one to calculate unambiguously without renormalization scale or
scheme ambiguity the effective charges of the polarized Bjorken and the
Gross-Llewellen Smith sum rules from the experimental value for the effective
charge associated with -ratio. Present data are consistent with the
generalized Crewther relations, but measurements at higher precision and
energies will be needed to decisively test these fundamental relations in QCD.Comment: 16 pages, LATEX fil
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