Analyticity and power corrections in hard-scattering hadronic functions

Demanding the analyticity of hadronic observables (calculated in terms of power series of the running coupling) as a whole, we show that they are free of the Landau singularity. Employing resummation and dispersion-relation techniques, we compute in a unifying way power corrections to two different hard-scattering functions in perturbative QCD: the electromagnetic pion form factor to leading order and the inclusive cross section of the Drell–Yan process. In the second case, the leading nonperturbative power correction in bΛQCD gives rise to a Sudakov-like exponential factor in the impact parameter space which provides enhancement rather than suppression.