4,328 research outputs found
Anomalous dimension of gluonic operator in polarized deep inelastic scattering at O(1/N_f)
We compute the O(1/N_f) correction to the predominantly gluonic flavour
singlet twist-2 anomalous dimension used in polarized deep inelastic
scattering. It is consistent with known two loop perturbation theory and we
determine the three loop contribution at O(1/N_f). The treatment of the
epsilon-tensor in the large N_f d-dimensional critical point formalism is also
discussed.Comment: 8 Latex pages, 1 postscript figur
Structure function evolution at next-to-leading order and beyond
Results are presented of two studies addressing the scaling violations of
deep-inelastic structure functions. Factorization-scheme independent fits to
all ep and mu p data on F_2 are performed at next-to-leading order (NLO),
yielding alpha_s(M_Z) = 0.114 +- 0.002_exp (+0.006-0.004)_th . In order to
reduce the theoretical error dominated by the renormalization-scale dependence,
the next-higher order (NNLO) needs to be included. For the flavour non-singlet
sector, it is shown that available calculations provide sufficient information
for this purpose at x > 10^-2.Comment: 3 pages LaTeX including 4 eps-figures, uses npb.sty. Talk presented
at DIS'99, DESY-Zeuthen, April 1999. To appear in the proceeding
The 4-loop quark mass anomalous dimension and the invariant quark mass
We present the analytical calculation of the four-loop quark mass anomalous
dimension in Quantum Chromodynamics within the minimal subtraction scheme. On
the basis of this result we find that the so-called invariant quark mass is a
very good reference mass for the accurate evolution of the running MS-bar quark
mass in phenomenological applications. We also obtain for the first time a
complete 4-th order perturbative QCD expression for a physical quantity, the
total Higgs boson decay rate into hadrons, and analyze the infrared fixed point
for this case.Comment: 11 pages, Late
On the role of the quark mass thresholds in extrapolations of the running \alpha_s
The accuracy of the conventional treatment of quark mass thresholds in the
QCD running coupling constant , based on the step approximation to
the --function, is investigated. The errors of extrapolating \ase(\mu)
from low energies to , implied by this approximation, are shown to be
of the same magnitude as the typical next--to--next--to--leading order
contributions to \as and tend to increase the resulting \as. The importance of
the proper choice of matching points is emphasized.Comment: latex, 7 pages, 2 uuencoded figure
The 16th Moment of the Non--Singlet Structure Functions and to
We present the results of an analytic next--to--next--to leading order QCD
calculation of the non--singlet anomalous dimension and
the coefficient functions associated to the deeply inelastic
structure functions and for the Mellin moment N=16.
Comparisons are made with results in the literature.Comment: 11 pages, 1 style file, 1 figur
Matching QCD and HQET at three loops
QCD/HQET matching for the heavy-quark field and heavy-light quark currents
with three-loop accuracy is discussed.Comment: Talk at Loops and Legs 2010, Woerlitz, 25-30 April, 7 pages; v2:
references adde
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