Power Corrections in QCD: A Matter of Energy Resolution

We consider power-like corrections in QCD which can be viewed as power surpressed infrared singularities. We argue that the presence of these singularities depends crucially on the energy resolution. In case of poor energy resolution, i.e., inclusive cross sections, there are constraints on infrared singularities expressed by the Kinoshita-Lee-Nauenberg (KLN) theorem. We rewrite the theorem in covariant notations and argue that the KLN theorem implies the extension of the Bloch-Nordsieck cancellation of logarithmic singularities to the case of linear corrections.