60 research outputs found
Modified Wandzura-Wilczek Relation with the Nachtmann Variable
If one retains M^2/Q^2 terms in the kinematics, the Nachtmann variable \xi
seems to be more appropriate to describe deep inelastic lepton-nucleon
scattering. Up to the first power of M^2/Q^2, a modified Wandzura-Wilczek
relation with respect to \xi was derived. Kinematical correction factors are
given as functions of \xi and Q^2. A comparison of the modified g_2^WW(\xi) and
original g_2^WW(x) with the most recent g_2 data is shown.Comment: 10 pages, 3 figures, revised version with minor correction
Power Counting in the Soft-Collinear Effective Theory
We describe in some detail the derivation of a power counting formula for the
soft-collinear effective theory (SCET). This formula constrains which operators
are required to correctly describe the infrared at any order in the
Lambda_QCD/Q expansion (lambda expansion). The result assigns a unique
lambda-dimension to graphs in SCET solely from vertices, is gauge independent,
and can be applied independent of the process. For processes with an OPE the
lambda-dimension has a correspondence with dynamical twist.Comment: 12 pages, 1 fig, journal versio
Resonances and higher twist in polarized lepton-nucleon scattering
We present a detailed analysis of resonance contributions in the context of
higher twist effects in the moments of the proton spin structure function g_1.
For each of these moments, it is found that there exists a characteristic Q^2
region in which (perturbative) higher twist corrections coexist with
(non-perturbative) resonance contribution of comparable magnitude.Comment: 17 pages LaTe
The Systematical Uncertainties in Measurements of the Spin-Dependent Structure Function g1n with He-3 Target due to Radiative Correction Procedure
The sources of the systematical uncertainties due to radiative correction
procedure in measurements of the structure function with He target
are considered. Their numerical estimations are presented. The relative
systematical uncertainty does not exceed 5%.Comment: 6 pages, 2 figure
Twist-2 Heavy Flavor Contributions to the Structure Function
The twist--2 heavy flavor contributions to the polarized structure function
are calculated. We show that this part of is related
to the heavy flavor contribution to by the Wandzura--Wilczek
relation to all orders in the strong coupling constant. Numerical results are
presented.Comment: 17 pages LATEX, 1 style files, 4 figure
The Spin-Dependent Structure Functions of Nuclei in the Meson-Nucleon Theory
A theoretical approach to the investigation of spin-dependent structure
functions in deep inelastic scattering of polarized leptons off polarized
nuclei, based on the effective meson-nucleon theory and operator product
expansion method, is proposed and applied to deuteron and . The explicit
forms of the moments of the deuteron and spin-dependent structure
functions are found and numerical estimates of the influence of nuclear
structure effects are presented.Comment: 42 pages revtex, 7 postscript figures available from above e-mail
upon request. Perugia preprint DFUPG 92/9
A lattice calculation of the nucleon's spin-dependent structure function g_2 revisited
Our previous calculation of the spin-dependent structure function g_2 is
revisited. The interest in this structure function is to a great extent
motivated by the fact that it receives contributions from twist-two as well as
from twist-three operators already in leading order of 1/Q^2 thus offering the
unique possibility of directly assessing higher-twist effects. In our former
calculation the lattice operators were renormalized perturbatively and mixing
with lower-dimensional operators was ignored. However, the twist-three operator
which gives rise to the matrix element d_2 mixes non-perturbatively with an
operator of lower dimension. Taking this effect into account leads to a
considerably smaller value of d_2, which is consistent with the experimental
data.Comment: 25 pages, 11 figure
Leading and higher twists in the proton polarized structure function at large Bjorken x
A phenomenological parameterization of the proton polarized structure
function has been developed for x > 0.02 using deep inelastic data up to ~ 50
(GeV/c)**2 as well as available experimental results on both photo- and
electro-production of proton resonances. According to the new parameterization
the generalized Drell-Hearn-Gerasimov sum rule is predicted to have a
zero-crossing point at Q**2 = 0.16 +/- 0.04 (GeV/c)**2. Then, low-order
polarized Nachtmann moments have been estimated and their Q**2-behavior has
been investigated in terms of leading and higher twists for Q**2 > 1
(GeV/c)**2. The leading twist has been treated at NLO in the strong coupling
constant and the effects of higher orders of the perturbative series have been
estimated using soft-gluon resummation techniques. In case of the first moment
higher-twist effects are found to be quite small for Q**2 > 1 (GeV/c)**2, and
the singlet axial charge has been determined to be a0[10 (GeV/c)**2] = 0.16 +/-
0.09. In case of higher order moments, which are sensitive to the large-x
region, higher-twist effects are significantly reduced by the introduction of
soft gluon contributions, but they are still relevant at Q**2 ~ few (GeV/c)**2
at variance with the case of the unpolarized transverse structure function of
the proton. Our finding suggests that spin-dependent correlations among partons
may have more impact than spin-independent ones. As a byproduct, it is also
shown that the Bloom-Gilman local duality is strongly violated in the region of
polarized electroproduction of the Delta(1232) resonance.Comment: revised version to appear in Phys. Rev. D; extended discussion on the
generalized DHG sum rul
Polarized Virtual Photon Structure Function and Twist-3 Effects in QCD
We investigate the twist-3 effects in the polarized virtual photon structure.
The structure functions and of polarized photon could
be experimentally studied in the future polarized or colliders.
The leading contributions to are the twist-2 effects, while
another structure function , which only exists for the virtual
photon target, receives not only the twist-2 but also twist-3 contributions. We
first show that the twist-3 effects actually exist in the box-diagram
contributions and we extract the twist-3 part, which can also be reproduced by
the pure QED operator product expansion. We then calculate the non-trivial
lowest moment () of the twist-3 contribution to in QCD. For
large (the number of colors), the QCD analysis of the twist-3 effects in
the flavor nonsinglet part of becomes tractable and we can obtain
its moments in a compact form for all .Comment: 27 pages, LaTeX, 9 eps figures, eqsection.sty file included, Appendix
A added, some minor changes for Fig.
A QCD Analysis of Polarised Parton Densities
We present the results of a QCD fit to global data on deep-inelastic
polarised lepton-hadron scattering. We find that it is possible to fit the data
with strongly broken SU(2) flavour for the polarised sea densities. This can
easily be tested in production at polarised RHIC. The data fails to pin
down polarised singlet sea quark and gluon densities. We explore the
uncertainties in detail and show that improvement in statistics, achievable at
polarised HERA for measurement of A_1 at moderately low values of x, have large
payoffs in terms of the improvement in measurement of gluon and sea quark
densities.Comment: Revtex 17 pages, 19 postscript figures. Analysis extended to SU(2)
flavour symmetric and nonsymmetric se
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