Universality and Scaling in Perturbative QCD at Small x
Abstract
We present a pedagogical review of the universal scaling properties displayed by the structure function F_2 at small x and large Q^2 as measured at HERA. We first describe the derivation of the double asymptotic scaling of F_2 from the leadingorder AltarelliParisi equations of perturbative QCD. Universal nexttoleading order corrections to scaling are also derived. We explain why the universal scaling behaviour is spoiled when the initial distributions rise too steeply by considering the nonsinglet distribution F_2^pF_2^n as an explicit example. We then examine the stability of double scaling to the inclusion of higher order singularities, explaining how the perturbative expansion at small x can be reorganized in such a way that each order is given by the sum of a convergent series of contributions which are of arbitrarily high order in the coupling. The wavelike nature of perturbative evolution is then shown to persist throughout almost all the small x region, giving rise asymptotically to double scaling for a wide class of boundary conditions.
 Publication:

arXiv eprints
 Pub Date:
 December 1995
 arXiv:
 arXiv:hepph/9512208
 Bibcode:
 1995hep.ph...12208F
 Keywords:

 High Energy Physics  Phenomenology
 EPrint:
 35 pages, TeX with epsf, 12 figures in compressed postscript