1,183 research outputs found
On parton number fluctuations at various stages of the rapidity evolution
Starting with the interpretation of parton evolution with rapidity as a
branching-diffusion process, we describe the different kinds of fluctuations of
the density of partons which affect the properties of QCD scattering amplitudes
at moderately high energies. We then derive some of these properties as direct
consequences of the stochastic picture. We get new results on the expression of
the saturation scale of a large nucleus, and a modified geometric scaling valid
at intermediate rapidities for dipole-dipole scattering.Comment: 18 pages, 3 figures. v2: Improved writing; In particular, extended
discussion of the dipole-dipole case in Sec. 4. A few misprints corrected. To
appear in Phys. Lett.
Phenomenology on the QCD dipole picture revisited
We perform an adjust to the most recent structure function data, considering
the QCD dipole picture applied to ep scattering. The structure function F2 at
small x and intermediate Q2 can be described by the model containing an
economical number of free-parameters, which encodes the hard Pomeron physics.
The longitudinal structure function and the gluon distribution are predicted
without further adjustments. The data description is effective, whereas a
resummed next-to-leading level analysis is deserved.Comment: 18 pages, 6 figures. Version to be published in Eur. Phys. J.
QCD saturation in the dipole sector with correlations
In this paper we study the description of saturation in Balitsky,
Jalilian-Marian, Iancu, McLerran, Weigert, Leonidov and Kovner (B-JIMWLK)
picture when restricted to observables made up only from dipole operators. We
derive a functional form of the evolution equation for the dipole probability
distribution and find a one-parameter family of exact solutions to the dipole
evolution equations.Comment: 9 pages, v2: references and comments added, v3: version to appear in
Phys. Lett. B (title changed in journal
Universality and tree structure of high energy QCD
Using non-trivial mathematical properties of a class of nonlinear evolution
equations, we obtain the universal terms in the asymptotic expansion in
rapidity of the saturation scale and of the unintegrated gluon density from the
Balitsky-Kovchegov equation. These terms are independent of the initial
conditions and of the details of the equation. The last subasymptotic terms are
new results and complete the list of all possible universal contributions.
Universality is interpreted in a general qualitative picture of high energy
scattering, in which a scattering process corresponds to a tree structure
probed by a given source.Comment: 4 pages, 3 figure
A phenomenological theory giving the full statistics of the position of fluctuating pulled fronts
We propose a phenomenological description for the effect of a weak noise on
the position of a front described by the Fisher-Kolmogorov-Petrovsky-Piscounov
equation or any other travelling wave equation in the same class. Our scenario
is based on four hypotheses on the relevant mechanism for the diffusion of the
front. Our parameter-free analytical predictions for the velocity of the front,
its diffusion constant and higher cumulants of its position agree with
numerical simulations.Comment: 10 pages, 3 figure
Scaling Phenomena in Gravity from QCD
We present holographic arguments to predict properties of strongly coupled
gravitational systems in terms of weakly coupled gauge theories. In particular
we relate the latest computed value for the Choptuik critical exponent in black
hole formation in five dimensions, \gamma_{5D}=0.412 \pm 1%, to the saturation
exponent of four-dimensional Yang-Mills theory in the Regge limit,
\gamma_{BFKL}\simeq 0.410.Comment: 13 pages. To Pere Pascual, in memoriam. v2: minor changes. Typos
corrected and references added. v3: conclusions expanded, references added.
To appear in Physics Letters
Diffractive photon dissociation in the saturation regime from the Good and Walker picture
Combining the QCD dipole model with the Good and Walker picture, we formulate
diffractive dissociation of a photon of virtuality Q^2 off a hadronic target,
in the kinematical regime in which Q is close to the saturation scale and much
smaller than the invariant mass of the diffracted system. We show how the
obtained formula compares to the HERA data and discuss what can be learnt from
such a phenomenology. In particular, we argue that diffractive observables in
these kinematics provide useful pieces of information on the saturation regime
of QCD.Comment: 17 pages, 7 figures, revte
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