Vacuum fluctuations and impulse approximation in QCD

Abstract

We ask whether the idea of factorization can be extended, in the presence of vacuum fluctuations, to general hard processes in QCD. Using simple examples we discuss the difficulties in defining parton cross sections and the way in which infrared divergences cancel. These arguments show that the impulse approximation valid in the leading order of QCD cannot be generalized in a straightforward manner to higher twists.