Breakdown of Dimensional Regularization in the Sudakov Problem
  An explicit example is presented (a one-loop triangle graph) where dimensional regularization fails to regulate the infra-red singularities that emerge at intermediate steps of studying large-$Q^2$ Sudakov factorization. The mathematical nature of the phenomenon is explained within the framework of the theory of the $As$-operation. 
J.C. Collins and F.V. Tkachov