Saturation and universality in QCD at small x

We find approximate solutions to the renormalization group equation which g overns the quantum evolution of the effective theory for the Color Glass Co ndensate. This is a functional Fokker-Planck equation which generates in pa rticular the non-linear evolution equations previously derived by Balitsky and Kovchegov within perturbative QCD. In the limit where the transverse mo mentum of the external probe is large compared to the saturation momentum, our approximations yield the Gaussian ansatz for the effective action of th e McLerran-Venugopalan model. In the opposite limit, of a small external mo mentum, we find that the effective theory is governed by a scale-invariant universal action which has the correct properties to describe gluon saturat ion. (C) 2001 Elsevier Science B.V. All rights reserved.