482 research outputs found
Photon impact factor in the next-to-leading order
An analytic coordinate-space expression for the next-to-leading order photon
impact factor for small- deep inelastic scattering is calculated using the
operator expansion in Wilson lines.Comment: 5 pages, 3 figure
Photon impact factor and -factorization for DIS in the next-to-leading order
The photon impact factor for the BFKL pomeron is calculated in the
next-to-leading order (NLO) approximation using the operator expansion in
Wilson lines. The result is represented as a NLO -factorization formula
for the structure functions of small- deep inelastic scattering.Comment: 13 pages, 4 figures, typos corrected. arXiv admin note: substantial
text overlap with arXiv:1009.472
Light-cone sum rules for the transitions for real photons
We examine the radiative transition at the real photon
point using the framework of light-cone QCD sum rules. In particular,
the sum rules for the transition form factors and are
determined up to twist 4. The result for agrees with experiment within
10% accuracy. The agreement for is also reasonable. In addition, we
derive new light-cone sum rules for the magnetic moments of nucleons, with a
complete account of twist-4 corrections based on a recent reanalysis of photon
distribution amplitudes.Comment: 34 pages, 9 figures, revised version, published in Phys. Rev. D, one
misplaced reference correcte
Deep inelastic scattering and prompt photon production within the framework of quark Reggeization hypothesis
We study ep deep inelastic scattering and the inclusive production of prompt
photon within the framework of the quasi-multi-Regge-kinematic approach,
applying the quark Reggeization hypothesis. We describe structure functions F_2
and F_L supposing that a virtual photon scatters on a Reggeized quark from a
proton, via the effective gamma-Reggeon-quark vertex. It is shown that the main
mechanism of the inclusive prompt photon production in p \bar p collisions is
the fusion of a Reggeized quark and a Reggeized antiquark into a photon, via
the effective Regeon-Reggeon-gamma vertex. We describe the inclusive photon
transverse momentum spectra measured by the CDF and D0 Collaborations within
errors and without free parameters, using the Kimber-Martin-Ryskin unintegrated
quark and gluon distribution functions in a proton.Comment: 13 pages, 10 figure
Renormalons as dilatation modes in the functional space
There are two sources of the factorial large-order behavior of a typical
perturbative series. First, the number of the different Feynman diagrams may be
large; second, there are abnormally large diagrams known as renormalons. It is
well known that the large combinatorial number of diagrams is described by
instanton-type solutions of the classical equations. We demonstrate that from
the functional-integral viewpoint the renormalons do not correspond to a
particular configuration but manifest themselves as dilatation modes in the
functional space.Comment: 19 pages, latex, 5 eps figure
Magnetic Susceptibility of the Quark Condensate and Polarization from Chiral Models
We compute the magnetic susceptibility of the quark condensate and the
polarization of quarks at zero temperature and in a uniform magnetic
background. Our theoretical framework consists of two chiral models that allow
to treat self-consistently the spontaneous breaking of chiral symmetry: the
linear model coupled to quarks, dubbed quark-meson model, and the
Nambu-Jona-Lasinio model. We also perform analytic estimates of the same
quantities within the renormalized quark-meson model, both in the regimes of
weak and strong fields. Our numerical results are in agreement with the recent
literature; moreover, we confirm previous Lattice findings, related to the
saturation of the polarization at large fields.Comment: 13 pages, 4 figure
Gluon recombination in high parton density QCD: inclusive pion production
We argue that the collinear factorization of the fragmentation functions in
high energy hadron and nuclei collisions breaks down at transverse momenta kT <
Qs/g due to high parton densities in the colliding hadrons and/or nuclei. We
calculate, at next-to-leading order in projectile parton density and to all
orders in target parton density, the double-inclusive cross section for
production of a pair of gluons in the scalar J^(PC)=0^(++) channel. Using the
low energy theorems of QCD we find the inclusive cross section for pi-meson
production.Comment: 24 pages, 5 figure
Exotic hybrid mesons in hard electroproduction
We estimate the sizeable cross section for deep exclusive electroproduction
of an exotic hybrid meson in the Bjorken regime. The production
amplitude scales like the one for usual meson electroproduction, i.e. as
. This is due to the non-vanishing leading twist distribution amplitude
for the hybrid meson, which may be normalized thanks to its relation to the
energy momentum tensor and to the QCD sum rules technique. The hard amplitude
is considered up to next-to-leading order in and we explore the
consequences of fixing the renormalization scale ambiguity through the BLM
procedure. We study the particular case where the hybrid meson decays through a
meson pair. We discuss the generalized distribution
amplitude and then calculate the production amplitude for this process. We
propose a forward-backward asymmetry in the production of and
mesons as a signal for the hybrid meson production. We briefly comment on
hybrid electroproduction at very high energy, in the diffractive limit where a
QCD Odderon exchange mechanism should dominate. The conclusion of our study is
that hard electroproduction is a promissing way to study exotic hybrid mesons,
in particular at JLAB, HERA (HERMES) or CERN (Compass)
Inclusive Gluon Production In High Energy Onium-Onium Scattering
We calculate the inclusive single-gluon production cross section in high
energy onium-onium scattering including pomeron loop effects. The resulting
inclusive cross section is given by the k_T-factorization formula with one of
the unintegrated gluon distribution functions depending on the total
onium-onium scattering cross section, which includes all pomeron loops and has
to be found independently. We discuss the limits of applicability of our result
and argue that they are given by the limits of applicability of pomeron loop
resummation approach. Since the obtained k_T-factorization formula is infrared
divergent we conclude that, in order to consistently calculate the
(infrared-finite) gluon production cross section in onium-onium scattering, one
has to include corrections going beyond the pomeron loop approximation.Comment: 20 pages, 6 figures; v2: version accepted to Phys. Rev. D, minor
corrections include
Exclusive photoproduction of hard dijets and magnetic susceptibility of QCD vacuum
We argue that coherent production of hard dijets by linearly polarized real
photons can provide direct evidence for chirality violation in hard processes,
the first measurement of the magnetic susceptibility of the quark condensate
and the photon distribution amplitude. It can also serve as a sensitive probe
of the generalized gluon parton distribution. Numerical calculations are
presented for HERA kinematics.Comment: 4 pages, 4 figure
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