From Altarelli-Parisi to Lipatov round trip

by Stefano Forte (Università di Milano)

Friday 29 Aug 2003, 14:00 → 15:00 Europe/Zurich

TH Auditorium (CERN)

I present a general account of recent progress in the understanding of the small-x resummation of QCD evolution equations. I show that the well-known phenomenological success of conventional two-loop evolution at small x is now understood to be a consequence of the BFKL resummation of the Altarelli-Parisi equation. This surprising result follows from the realization that the Altarelli-Parisi and BFKL equations are fully compatible, and can be used to resum each other. The main physical ingredients of the resummation are momentum conservation and the running of the coupling. I show that, when incorporated in the standard leading order BFKL formalism, they unambiguously lead to predictions which at small x are very close to the usual one-loop unresummed results, and stable towards the inclusion of higher-order corrections.