Evidence for infrared finite coupling in Sudakov resummation
  New arguments are presented in favor of the infrared finite coupling approach to power corrections in the context of Sudakov resummation. The more regular infrared behavior of some peculiar combinations of Sudakov anomalous dimensions, free of Landau singularities at large Nf, is pointed out. A general conflict between the infrared finite coupling and infrared renormalon approaches to power corrections is explained, and a possible resolution is proposed, which makes use of the arbitrariness of the choice of constant terms in the Sudakov exponent. A simple ansatz for a `universal' non-perturbative Sudakov effective coupling at large Nf emerges naturally from these considerations. An alternative evidence for an infrared finite {\em perturbative} effective coupling in the Drell-Yan process at large Nf (albeit at odds with the infrared renormalon argument) is found within the framework of Sudakov resummation for eikonal cross sections of Laenen, Sterman and Vogelsang. 
Georges Grunberg