Extending the QCD Perturbative Domain to Higher Energies

After a brief introduction to low-x QCD and to resummation approaches, I illustrate the predictions for the gluon Green function and splitting function of a recent renormalization-group improved small-x resummation scheme. I argue, on this basis, that the range of validity of perturbative calculations is considerably extended in rapidity with respect to leading log expectations. The perturbative high-energy exponents are predicted in a phenomenologically interesting range, and significant preasymptotic effects are found. In particular, the splitting function shows a shallow dip in the moderate-x region, followed by the expected small-x power increase.

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