634 research outputs found
Total gluon shadowing due to fluctuation effects
We show a new physical phenomenon expected for the ratio R_{pA} of the
unintegrated gluon distribution of a nucleus over the unintegrated gluon
distribution of a proton scaled up by the atomic factor A^{1/3} in the
fluctuation-dominated (diffusive scaling) region at high energy. We calculate
the dependence of R_{pA} on the atomic number A, the rapidity Y and the
transverse gluon momentum k_{\perp}. We find that R_{pA} exhibits an increasing
gluon shadowing with growing rapidity, approaching 1/A^{1/3} at asymptotic
rapidities which means total gluon shadowing, due to the effect of gluon number
fluctuations or Pomeron loops. The increase of R_{pA} with rising gluon
momentum decreases as the rapidity grows. In contrast, in the geometric scaling
region where the effect of fluctuations is negligible, the ratio R_{pA} shows
only partial gluon shadowing in the fixed-coupling case, basically independent
on the rapidity and the gluon momentum.Comment: 12 pages, 1 figure; two plots and further explanations added; matches
version accepted for publicatio
High-enegy effective action from scattering of QCD shock waves
At high energies, the relevant degrees of freedom are Wilson lines - infinite
gauge links ordered along straight lines collinear to the velocities of
colliding particles. The effective action for these Wilson lines is determined
by the scattering of QCD shock waves. I develop the symmetric expansion of the
effective action in powers of strength of one of the shock waves and calculate
the leading term of the series. The corresponding first-order effective action,
symmetric with respect to projectile and target, includes both up and down fan
diagrams and pomeron loops.Comment: 15 pages, 10 eps figure
Dense-Dilute Duality at work: dipoles of the target
We explore the properties of the QCD high energy evolution in the limit of a
dilute target. Using the recently established property of selfduality of the
evolution operator (hep-ph/0502119), we show how to properly define the target
gluon and dipole creation operators in terms of dual Wilson lines (dual eikonal
factors). We explain how to expand these operators in terms of the functional
derivatives of the color charge density, in the situation when they act on the
eikonal factors of the projectile partons. We explicitly calculate the
expansion of the high energy evolution operator to fourth order in the
functional derivatives. Our result is infrared and ultraviolet finite, but does
not coincide with the formula given in hep-ph/0501088. We resolve this
discrepancy by showing that the identification of the dipole creation and
annihilation operators used in hep-ph/0501088 is incomplete, and provide the
required corrections to these definitions. The use of the corrected operators
in the calculational framework of hep-ph/0501088 reproduces our result. We also
prove that there is no discrepancy between the expansion of the JIMWLK equation
and the dualization of the expansion of the weak field limit.Comment: 18 pages, Explanations added. Version to appear in PR
JIMWLK evolution in the Gaussian approximation
We demonstrate that the Balitsky-JIMWLK equations describing the high-energy
evolution of the n-point functions of the Wilson lines (the QCD scattering
amplitudes in the eikonal approximation) admit a controlled mean field
approximation of the Gaussian type, for any value of the number of colors Nc.
This approximation is strictly correct in the weak scattering regime at
relatively large transverse momenta, where it reproduces the BFKL dynamics, and
in the strong scattering regime deeply at saturation, where it properly
describes the evolution of the scattering amplitudes towards the respective
black disk limits. The approximation scheme is fully specified by giving the
2-point function (the S-matrix for a color dipole), which in turn can be
related to the solution to the Balitsky-Kovchegov equation, including at finite
Nc. Any higher n-point function with n greater than or equal to 4 can be
computed in terms of the dipole S-matrix by solving a closed system of
evolution equations (a simplified version of the respective Balitsky-JIMWLK
equations) which are local in the transverse coordinates. For simple
configurations of the projectile in the transverse plane, our new results for
the 4-point and the 6-point functions coincide with the high-energy
extrapolations of the respective results in the McLerran-Venugopalan model. One
cornerstone of our construction is a symmetry property of the JIMWLK evolution,
that we notice here for the first time: the fact that, with increasing energy,
a hadron is expanding its longitudinal support symmetrically around the
light-cone. This corresponds to invariance under time reversal for the
scattering amplitudes.Comment: v2: 45 pages, 4 figures, various corrections, section 4.4 updated, to
appear in JHE
Pomeron loops in zero transverse dimensions
We analyze a toy model which has a structure similar to that of the recently
found QCD evolution equations, but without transverse dimensions. We develop
two different but equivalent methods in order to compute the leading-order and
next-to-leading order Pomeron loop diagrams. In addition to the leading-order
result which has been derived from Mueller's toy model~\cite% {Mueller:1994gb},
we can also calculate the next-to-leading order contribution which provides the
correction. We interpret this result and discuss its
possible implications for the four-dimensional QCD evolution.Comment: 11 pages, 4 figure
Drell-Yan production and Lam-Tung relation in the Color Glass Condensate formalism
We study the Drell-Yan production cross section and structure functions in
proton (deuteron)-nucleus collisions using the Color Glass Condensate
formalism. The nucleus is treated in the Color Glass Condensate framework which
includes both higher twist effects due to the inclusion of multiple scatterings
and leading twist pQCD shadowing due to the small x resummation, while the
proton (or deuteron) is treated within the DGLAP improved parton model. In
particular, the Drell-Yan structure functions are used in order to investigate
the Lam-Tung relation at small x, which is known to be identically zero at
leading twist up to Next-to-Leading order, and is thus a good playground for
studying higher twist effects. In agreement with this, we find that violations
of this relation are more important for low momentum and invariant mass of the
Drell-Yan pair, and also in the region of rapidity that corresponds to smaller
values of x in the nucleus.Comment: 25 pages, 16 postscript figure
Selection of human capital in metallurgical companies using information technology (IT)
Personnel selection is a process that takes place in a company in order to have better business performance and competitive advantage. Nowadays, companies have realized the importance of human capital as a necessity for survival in today’s competitive market. There are several methods for selecting staff, but this paper seeks to demonstrate that this selection can be done with the help of an expert system. Metallurgical companies face even greater challenges for managing personnel selection. This research will discover and test the key elements of management personnel selection and implementation of an expert system
Fluctuations effects in high-energy evolution of QCD
Recently, Iancu and Triantafyllopoulos have proposed a hierarchy of evolution
equations in QCD at high energy which generalises previous approaches by
including the effects of gluon number fluctuations and thus the pomeron loops.
In this paper, we present the first numerical simulations of the Langevin
equation which reproduces that hierarchy. This equation is formally the
Balitsky-Kovchegov equation supplemented with a noise term accounting for the
relevant fluctuations. In agreement with theoretical predictions, we find that
the effects of the fluctuations is to reduce the saturation exponent and to
induce geometric scaling violations at high energy.Comment: 12 pages, 7 figures, minor corrections, version appeared in Phys.
Rev.
Diffractive dissociation including pomeron loops in zero transverse dimensions
We have recently studied the QCD pomeron loop evolution equations in zero
transverse dimensions [Shoshi:2005pf]. Using the techniques developed in
[Shoshi:2005pf] together with the AGK cutting rules, we present a calculation
of single, double and central diffractive cross sections (for large diffractive
masses and large rapidity gaps) in zero transverse dimensions in which all
dominant pomeron loop graphs are consistently summed. We find that the
diffractive cross sections unitarise at asymptotic energies and that they are
suppressed by powers of alpha_s. Our calculation is expected to expose some of
the diffractive physics in hadron-hadron collisions at high energy.Comment: 14 pages, 5 figures; numerous explanations added, matches the
published versio
On Angular Correlations and High Energy Evolution
We address the question to what extent JIMWLK evolution is capable of taking
into account angular correlations in a high energy hadronic wave function. Our
conclusion is that angular (and indeed other) correlations in the wave function
cannot be reliably calculated without taking into account Pomeron loops in the
evolution. As an example we study numerically the energy evolution of angular
correlations between dipole scattering amplitudes in the framework of the large
approximation to JIMWLK evolution (the "`projectile dipole model"').
Target correlations are introduced via averaging over (isotropic) ensemble of
anisotropic initial conditions. We find that correlations disappear very
quickly with rapidity even inside the saturation radius. This is in accordance
with our physical picture of JIMWLK evolution. The actual correlations inside
the saturation radius in the target QCD wave function, on the other hand should
remain sizable at any rapidity.Comment: 12 pages, 11 figure
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