274 research outputs found
From QCD at high energy to statistical physics and back
In these proceedings, we shall first recall the evolution equations arising
when increasing the rapidity within the perturbative QCD regime. We
shall then summarise the main properties on their asymptotic solutions and
discuss the physical picture emerging from our analysis.Comment: 4 pages, talk presented at the DIS2006 meeting, April 19-24, Tsukuba,
Japa
Saturation in High-energy QCD
In these proceedings, I shall review the basic concepts of perturbative QCD in its high-energy limit, emphasising the approach to the unitarity limit, usually referred to as {\em saturation}. I shall explain the basic framework showing the need for saturation, first, from a simple picture of the high-energy behaviour, then, giving a short derivation of the equation driving this evolution. In the second part, I shall exhibit an analogy with statistical physics and show how this allows to derive {\em geometric scaling} in QCD with saturation. I shall finally consider the effects of gluon-number fluctuations on this picture
Testing the Gaussian Approximation to the JIMWLK Equation
In processes involving small-x partons, like in deep inelastic scattering and
in hadronic collisions at high energy, the final state can be expressed in
terms of correlators of Wilson lines. We study such high-point correlators
evolving according to the JIMWLK equation and we confirm the results of
previous numerical and analytic work, by using an independent method, that the
solution to the JIMWLK equation can be very well approximated by an appropriate
Gaussian wavefunction. We explore both fixed and running coupling evolution,
where in the latter the scale is set according to various prescriptions. As a
byproduct, we also numerically confirm to high accuracy the validity of the law
governing the behavior of the S-matrix close to the unitarity limit, the
Levin-Tuchin formula. We furthermore outline how to calculate correlators with
open color indices.Comment: 25 pages, 11 figures. v2: minor corrections, one equation added,
updated to match published versio
Pomeron loop and running coupling effects in high energy QCD evolution
Within the framework of a (1+1)-dimensional model which mimics evolution and
scattering in QCD at high energy, we study the influence of the running of the
coupling on the high-energy dynamics with Pomeron loops. We find that the
particle number fluctuations are strongly suppressed by the running of the
coupling, by at least one order of magnitude as compared to the case of a fixed
coupling, for all the rapidities that we have investigated, up to Y=200. This
reflects the slowing down of the evolution by running coupling effects, in
particular, the large rapidity evolution which is required for the formation of
the saturation front via diffusion. We conclude that, for all energies of
interest, processes like deep inelastic scattering or forward particle
production can be reliably studied within the framework of a mean-field
approximation (like the Balitsky-Kovchegov equation) which includes running
coupling effects.Comment: 23 pages, 8 figure
Diffusive foam wetting process in microgravity
We report the experimental study of aqueous foam wetting in microgravity. The
liquid fraction along the bubble edges is measured and is found to be a
relevant dynamical parameter during the capillary process. The penetration of
the liquid in the foam, the foam inflation, and the rigidity loss are shown all
to obey strict diffusion processes.Comment: 4 pages, 6 figures, submitted to Phys. Rev. Let
Resumming large higher-order corrections in non-linear QCD evolution
Linear and non-linear QCD evolutions at high energy suffer from severe issues
related to convergence, due to higher order corrections enhanced by large
double and single transverse logarithms. We resum double logarithms to all
orders by taking into account successive soft gluon emissions strongly ordered
in lifetime. We further resum single logarithms generated by the first
non-singular part of the splitting functions and by the one-loop running of the
coupling. The resulting collinearly improved BK equation admits stable
solutions, which are used to successfully fit the HERA data at small-x for
physically acceptable initial conditions and reasonable values of the fit
parameters.Comment: 4 pages, 4 figures, based on talk given at Hard Probes 2015, 29 June
- 3 July 2015, Montreal, Canad
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