POWER CORRECTIONS AND KLN CANCELLATIONS

We consider perturbative expansions in theories with an infrared cutof f lambda. The infrared sensitive parts are defined as terms non-analyt ic in infinitesimal lambda(2) and powers of this cutoff characterize t he strength of these infrared contributions. It is argued that the sum over the initial and final degenerate (as lambda --> 0) states, which is required by the Kinoshita-Lee-Nauenberg theorem, eliminates terms of order lambda(0) and lambda(1). However, the quadratic and higher or der terms in general do not cancel. This is investigated using simple examples of KLN cancellations, of relevance to the inclusive decay rat e of a heavy particle, at the one loop level. (C) 1998 Elsevier Scienc e B.V.