39 research outputs found
On The Pomeron at Large 't Hooft Coupling
We begin the process of unitarizing the Pomeron at large 't Hooft coupling.
We do so first in the conformal regime, which applies to good accuracy to a
number of real and toy problems in QCD. We rewrite the conformal Pomeron in the
-plane and transverse position space, and then work out the eikonal
approximation to multiple Pomeron exchange. This is done in the context of a
more general treatment of the complex -plane and the geometric consequences
of conformal invariance. The methods required are direct generalizations of our
previous work on single Pomeron exchange and on multiple graviton exchange in
AdS space, and should form a starting point for other investigations. We
consider unitarity and saturation in the conformal regime, noting elastic and
absorptive effects, and exploring where different processes dominate. Our
methods extend to confining theories and we briefly consider the Pomeron kernel
in this context. Though there is important model dependence that requires
detailed consideration, the eikonal approximation indicates that the Froissart
bound is generically both satisfied and saturated.Comment: 63 pages, 7 figures; published version: references updated and
several typos correcte
One gluon, two gluon: multigluon production via high energy evolution
We develop an approach for calculating the inclusive multigluon production
within the JIMWLK high energy evolution. We give a formal expression of
multigluon cross section in terms of a generating functional for arbitrary
number of gluons . In the dipole limit the expression simplifies
dramatically. We recover the previously known results for single and double
gluon inclusive cross section and generalize those for arbitrary multigluon
amplitude in terms of Feynman diagramms of Pomeron - like objects coupled to
external rapidity dependent field . We confirm the conclusion that the
AGK cutting rules in general are violated in multigluon production. However we
present an argument to the effect that for doubly inclusive cross section the
AGK diagramms give the leading contribution at high energy, while genuine
violation only occurs for triple and higher inclusive gluon production. We
discuss some general properties of our expressions and suggest a line of
argument to simplify the approach further.Comment: 32 pages, one reference corrected. to appear in JHE
Anisotropic flows from initial state of a fast nucleus
We analyze azimuthal anisotropy in heavy ion collisions related to the
reaction plane in terms of standard reggeon approach and find that it is
nonzero even when the final state interaction is switched off. This effect can
be interpreted in terms of partonic structure of colliding nuclei. We use
Feynman diagram analysis to describe details of this mechanism. Main
qualitative features of the appropriate azimuthal correlations are discussed.Comment: 16 pages, 11 figures. This paper is an extended version of a talk
given at Session of Nuclear Physics Division of Russian Academy of Sciences
in November 200
Inclusive 1-jet Production Cross Section at Small x in QCD: Multiple Interactions
We study corrections due to two Pomeron exchanges to the inclusive 1-jet
production cross section in the Regge limit of perturbative QCD for a finite
number of colors. By considering deep inelastic scattering on a weakly bound
two-nucleon system, we carefully follow the logic of the AGK cutting rules and
show, for the single inclusive cross section, that, due to the reggeization of
the gluon, modifications of the AGK cutting rules appear. As our main result,
we investigate and calculate the jet production vertex in the presence of a
two-Pomeron cut correction. Compared to previous studies, we find a novel
structure of the jet vertex which has not been considered before. We discuss a
few implications of this new piece.Comment: 42 pages, 22 figures, few references and comments added, to appear on
JHE
On asimuthal anisotropy in fragmentation of classical relativistic string
A fragmenting relativistic string is widely used for modelling particle
production via quark-gluon strings formed in hadron inelastic interactions of
high energies. In this note we focus on motion and fragmentation of
relativistic string with non-zero transverse separation of its ends and study
this scenario as a possible mechanism bringing anisotropy into the asimuthal
angle disribution of produced particles in inelastic interactions of hadrons.Comment: 12 pages, 6 figure
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.
Gluon distribution in proton at soft and hard pp collisions
We analyze the inclusive spectra of hadrons produced in collisions at
high energies in the mid-rapidity region within the soft QCD and perturbative
QCD assuming the possible creation of the soft gluons at low intrinsic
transverse momenta . From the best description of the LHC data we found
the parametrization of the unintegrated gluon distribution which at low
is different from the one obtained within the perturbative QCD.Comment: 10 pages, 5 figures. Talk given the 5th joint International HADRON
STRUCTURE '11 Conference (HS'11), Tatransk\'a Strba, Slovakia, June 27th -
July 1st, 201
Leading neutron spectra
It is shown that the observation of the spectra of leading neutrons from
proton beams can be a good probe of absorptive and migration effects. We
quantify how these effects modify the Reggeized pion-exchange description of
the measurements of leading neutrons at HERA. We are able to obtain a
satisfactory description of all the features of these data. We also briefly
discuss the corresponding data for leading baryons produced in hadron-hadron
collisions.Comment: 17 pages, 8 figures; sentence and reference added, reference
corrected, to be published in EPJ
A QCD motivated model for soft interactions at high energies
In this paper we develop an approach to soft scattering processes at high
energies,which is based on two mechanisms: Good-Walker mechanism for low mass
diffractionand multi-Pomeron interactions for high mass diffraction. The
pricipal idea, that allows us to specify the theory for Pomeron interactions,
is that the so called soft processes occur at rather short distances
(r^2 \propto 1 /^2 \propto \alpha'_\pom \approx 0.01 GeV^{-2}), where
perturbative QCD is valid. The value of the Pomeron slope \alpha'_\pom was
obtained from the fit to experimental data. Using this theoretical approach we
suggest a model that fits all soft data in the ISR-Tevatron energy range, the
total, elastic, single and double diffractive cross sections, including
dependence of the differential elastic cross section, and the mass dependence
of single diffraction. In this model we calculate the survival probability of
diffractive Higgs production, and obtained a value for this observable, which
is smaller than 1% at the LHC energy range.Comment: 33pp,20 figures in eps file
Nuclear shadowing in deep inelastic scattering on nuclei: leading twist versus eikonal approaches
We use several diverse parameterizations of diffractive parton distributions,
extracted in leading twist QCD analyses of the HERA diffractive deep inelastic
scattering (DIS) data, to make predictions for leading twist nuclear shadowing
of nuclear quark and gluon distributions in DIS on nuclei. We find that the
HERA diffractive data are sufficiently precise to allow us to predict large
nuclear shadowing for gluons and quarks, unambiguously. We performed detailed
studies of nuclear shadowing for up and charm sea quarks and gluons within
several scenarios of shadowing and diffractive slopes, as well as at central
impact parameters. We compare these leading twist results with those obtained
from the eikonal approach to nuclear shadowing (which is based on a very
different space-time picture) and observe sharply contrasting predictions for
the size and Q^2-dependence of nuclear shadowing. The most striking differences
arise for the interaction of small dipoles with nuclei, in particular for the
longitudinal structure function F_{L}^{A}.Comment: 43 pages, 16 figures, requires JHEP style fil