golem95: A numerical program to calculate one-loop tensor integrals with up to six external legs

Golem95: a numerical program to calculate one-loop tensor integrals with up to six external legs Abstract We present a program for the numerical evaluation of form factors entering the calculation of one-loop amplitudes with up to six external legs. The program is written in Fortran95 and performs the reduction to a certain set of basis integrals numerically, using a formalism where inverse Gram determinants can be avoided. It can be used to calculate one-loop amplitudes with massless internal particles in a fast and numerically stable way. PROGRAM SUMMARY Manuscript Title: Golem95: a numerical program to calculate one-loop diagrams with up to six external legs Computer: Any computer with a Fortran95 compiler Operating system: Linux, Unix RAM: RAM used per form factor is insignificant, even for a rank six six-point form factor Number of processors used: one Nature of problem: Evaluation of one-loop multi-leg tensor integrals occurring in the calculation of next-to-leading order corrections to scattering amplitudes in elementary particle physics. Solution method: Tensor integrals are represented in terms of form factors and a set of basic building blocks (" basis integrals "). The reduction to the basis integrals is performed numerically, thus avoiding the generation of large algebraic expressions. Restrictions: The current version contains basis integrals for massless internal particles only. Basis integrals for massive internal particles will be included in a future version. Running time: Depends on the nature of the problem. A rank 6 six-point form factor at a randomly chosen kinematic point takes 0.13 seconds on an Intel Core 2 Q9450 2.66 GHz processor.