High energy collisions allow to probe short-lived fluctuations in hadronic
or Nuclear Wave Functions. At high enough energy, the occupancy of the
resolved soft gluons becomes high and saturates. That nonlinear evolution
of the hadronic wave-functions has strong analogies with some reaction-
diffusion models. Borrowing some tools from statistical physics, one can
argue that the high energy asymptotics of the wave-functions is universal,
i.e. independent of the nature of the projectiles. Some of the universal
features of the solutions can be computed analytically despite the nonlinear
nature of the problem. After reviewing those results, I will present their
extension beyond the leading logarithmic approximation of QCD at high energy.