Reduction formalism for dimensionally regulated one-loop N-point integrals

We consider one-loop scalar and tensor integrals with an arbitrary number o f external legs relevant for multi-parton processes in massless theories. W e present a procedure to reduce N-point scalar functions with generic 4-dim ensional external momenta to box integrals in (4-2 epsilon) dimensions. We derive a formula valid for arbitrary N and give an explicit expression for N = 6. Further a tensor reduction method for N-point tensor integrals is presented . We prove that generically higher dimensional integrals contribute only to order epsilon for N greater than or equal to 5. The tensor reduction can b e solved iteratively such that any tensor integral is expressible in terms of scalar integrals. Explicit formulas are given up to N = 6. (C) 2000 Else vier Science B.V. All rights reserved.