On power corrections in the dispersive approach
  Power corrections in QCD (both conventional and unconventional ones arising from the ultraviolet region) are discussed within the infrared finite coupling-dispersive approach. It is shown how power corrections in Minkowskian quantities can be derived from the corresponding ones in associated Euclidean quantities through analyticity, allowing a parametrization in term of the Euclidean coupling and a renormalon-free perturbative expansion. It is argued that one should in general expect coefficients functions computed in the true non-perturbative vacuum to differ from the standard perturbative ones, even without assuming new physics. A phenomenology of $1/Q^2$ terms arising from eventual new physics of ultraviolet origin is also set-up. Models for non-perturbative contributions to the (universal) QCD coupling are suggested. Issues of renormalization scheme dependence are commented upon. 
G. Grunberg (Ecole Polytechnique)