Connections between high energy QCD and statistical physics

It has been proposed that the energy evolution of QCD amplitudes in the high-energy regime falls in the universality class of reaction-diffusion processes. We review the arguments for this correspondence, and we explain how it enables one to compute analytically asymptotic features of QCD amplitudes.Comment: 8 pages; To appear in the proceedings of 12th International Conference on Elastic and Diffractive Scattering, DESY, Hamburg, Germany, 21-25 May 200

Dipole-proton SS-matrix derived from diffractive meson electroproduction

Through a determination of the $S$-matrix element for the scattering of a localized colour dipole on a proton, we show that saturation effects can already be sizable at HERA. The saturation scale is found to be around 1-1.5 $GeV^2$ for the highest available energies and for central collisions, and is a decreasing function of the impact parameter.Comment: 4 pages, 1 figure (in eps) talk given at XXXI International Symposium on Multiparticle Dynamics, Sep. 1-7, 2001, Datong China URL http://ismd31.ccnu.edu.cn

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.