Is it Possible to Unify the QCD Evolution of Structure Functions in $X$ and $Q^2$ ?

Abstract

We start from the two existing QCD evolution equations for structure functions, the BFKL and DGLAP equations, and discuss the theoretical hints for a unifying picture of the evolution in $x$ and $Q^2.$ The main difficulty is due to the property of angular ordering of the gluon radiation driving the evolution and the cancellation of the related collinear singularities. At the leading $\log\ 1/x$ and leading $\log \ Q^2$ accuracy, we find a unified set of equations satisfying the constraints.