Power corrections and KLN cancellations Original Research Article

We consider perturbative expansions in theories with an infrared cutoff λ. The infrared sensitive parts are defined as terms non-analytic in infinitesimal λ2 and powers of this cutoff characterize the strength of these infrared contributions. It is argued that the sum over the initial and final degenerate (as λ → 0) states, which is required by the Kinoshita-Lee-Nauenberg theorem, eliminates terms of order λ0 and λ1. However, the quadratic and higher order terms in general do not cancel. This is investigated using simple examples of KLN cancellations, of relevance to the inclusive decay rate of a heavy particle, at the one loop level.