Factorization and Regularization by Dimensional Reduction

Since an old observation by Beenakker et al, the evaluation of QCD processes in dimensional reduction has repeatedly led to terms that seem to violate the QCD factorization theorem. We reconsider the example of the process gg → tt̄ and show that the factorization problem can be completely resolved. A natural interpretation of the seemingly non-factorizing terms is found, and they are rewritten in a systematic and factorized form. The key to the solution is that the Dand (4 − D)-dimensional parts of the 4-dimensional gluon have to be regarded as independent partons.