An algorithm for one-loop integrals with many external legs
Higher loop calculations are usually quite tedious and any progress in simplifying the task is welcomed. I developped an efficient algorithm for the reduction of multi-leg one-loop integrals (hep-ph/9811365). It has the advantage that it does not introduce Gram determinants in the denominator.
Dimensional regularization and four-dimensional spinors
Furthermore I developped a variant of dimensional regularization, which in practical calculations is as easy to use as dimensional reduction, but which is free of algebraic inconsistencies inherent in the latter one (hep-ph/9903380).
Cancellation of infrared divergences in processes with massive fermions
NLO calculations receive contributions from real emission and virtual one-loop corrections. Taken separately, each of the two terms gives a divergent contribution. Only the sum of the two is finite. A general purpose NLO Monte Carlo program requires therefore the cancellation of the infrared divergences before any numerical integration can be performed. Together with L. Phaf I extended the dipole formalism of Catani and Seymour to massive fermions (hep-ph/0102207).
Talks on this subject:
Talk given at Loops and Legs 2000
(hep-ph/0005283).