Perturbative QCD and Regge theory: closing the circle

Abstract We explain how Regge theory and perturbative evolution may be made compatible at small x . The result not only gives striking support to the two-pomeron description of small- x behaviour, but gives a rather clean test of perturbative QCD itself. When x is very small, the proton's gluon distribution function is significantly larger than is commonly believed. Perturbative evolution is invalid below Q 2 ≈5 GeV 2 .