21,046 research outputs found
On the initial condition for evolution of the perturbative QCD Pomeron in the nucleus
It is shown that subdominant terms found in the reggeized gluon diagram
technique, to be added to Pomeron fan diagrams with the 3P interaction, can be
exactly taken into account by taking the initial condition for evolution in the
Glauber form. This demonstrates complete equivalence of the dipole picture and
the reggeized gluon approach not only on the leading level but also on the
subleading level.Comment: 5 pages in LaTe
Production of a gluon with the exchange of three reggeized gluons in the Lipatov effective action approach
In the Regge kinematics the amplitude for gluon production off three
scattering centers is found in the Lipatov effective action technique. The
vertex for gluon emission with the reggeon splitting in three reggeons is
calculated and its transversality is demonstrated. It is shown that in the sum
of all contributions terms containing principal value singularities are
cancelled and substituted by the standard Feynman poles. These results may be
used for calculation of the inclusive cross-section for gluon production on two
nucleons in the nucleus.Comment: 22 pages, 9 figures; submitted to Eur.Phys.Jour.
Nucleon Form Factors and Distribution Amplitudes in QCD
We derive light-cone sum rules for the electromagnetic nucleon form factors
including the next-to-leading-order corrections for the contribution of
twist-three and twist-four operators and a consistent treatment of the nucleon
mass corrections. The essence of this approach is that soft Feynman
contributions are calculated in terms of small transverse distance quantities
using dispersion relations and duality. The form factors are thus expressed in
terms of nucleon wave functions at small transverse separations, called
distribution amplitudes, without any additional parameters. The distribution
amplitudes, therefore, can be extracted from the comparison with the
experimental data on form factors and compared to the results of lattice QCD
simulations. A selfconsistent picture emerges, with the three valence quarks
carrying 40%:30%:30% of the proton momentum.Comment: 27 pages, 7 figures uses revte
Axial form factor of the nucleon at large momentum transfers
Motivated by the emerging possibilities to study threshold pion
electroproduction at large momentum transfers at Jefferson Laboratory following
the 12 GeV upgrade, we provide a short theory summary and an estimate of the
nucleon axial form factor for large virtualities in the range using next-to-leading order light-cone sum rules.Comment: A comparison to the new neutrino data analysis and several references
added. Final version to appear in Phys.Rev.
The Reggeon 2 Reggeons Particle vertex in the Lipatov effective action formalism
The vertex for gluon emission during the splitting of a reggeized gluon into
two is constructed in the framework of Lipatov effective action formalism. Its
reduction to a pure transverse form for the diffractive amplitude gives the
standard Bartels vertex plus an additional contribution corresponding to the
emission from a pointlike splitting vertex. This additional contribution turns
out to be given by a longitudinal integral divergent both in the ultraviolet
and infrared. A certain specific recipe for this part, including the principal
value prescription for the integration, allows to eliminate this unwanted
contribution.Comment: 4 figures; misprints corrected; to be published in Eur.Phys.J.
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