The small-x behavior of structure functions in the saturation region is determined by the non-linear generalization of the BFKL equation. I suggest the effective field theory for the small-x evolution which solves formally this equation. The result is the 2 + 1 functional integral for the structure functions at small x. © 2001 Published by Elsevier Science B.V.
Balitsky, I. (2001). Effective field theory for the small-x evolution. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 518(3–4), 235–242. https://doi.org/10.1016/S0370-2693(01)01041-3