Exponentiation of the Drell-Yan an cross section near partonic threshold in the DIS and MS-bar schemes

It has been observed that in the DIS scheme the refactorization of the Drell-Yan cross section leading to exponentiation of threshold logarithms can also be used to organize a class of constant terms, most of which arise from the ratio of the timelike Sudakov form factor to its spacelike counterpart. We extend this exponentiation to include all constant terms, and demonstrate how a similar organization may be achieved in the MS-bar scheme. We study the relevance of these exponentiations in a two-loop analysis. (author)