Golem95C: A library for one-loop integrals with complex masses

G. Cullen

doi:10.1016/j.cpc.2011.05.015

2011-10-01

DOI：10.1016/j.cpc.2011.05.015

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We present a program for the numerical evaluation of scalar integrals and tensor form factors entering the calculation of one-loop amplitudes which supports the use of complex masses in the loop integrals. The program is built on an earlier version of the golem95 library, which performs the reduction to a certain set of basis integrals using a formalism where inverse Gram determinants can be avoided. It can be used to calculate one-loop amplitudes with arbitrary masses in an algebraic approach as well as in the context of unitarity-inspired numerical reconstruction of the integrand. Program summary Program title: golem95-1.2.0 Catalogue identifier: AEEO_v2_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEEO_v2_0.html Program obtainable from: CPC Program Library, Queen's University. Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 182 492 No. of bytes in distributed program, including test data, etc.: 950 549 Distribution format: tar.gz Programming language: Fortran95 Computer: Any computer with a Fortran95 compiler Operating system: Linux, Unix RAM: RAM used per integral/form factor is insignificant Classification: 4.4, 11.1 External routines: Some finite scalar integrals are called from OneLOop[1,2], the option to call them from LoopTools [3,4] is also implemented. Catalogue identifier of previous version: AEEO_v1_0 Journal reference of previous version: Comput. Phys. Comm. 180 (2009) 2317 Does the new version supersede the previous version?: Yes Nature of problem: Evaluation of one-loop multi-leg integrals occurring in the calculation of next-to-leading order corrections to scattering amplitudes in elementary particle physics. In the presence of massive particles in the loop, propagators going on-shell can cause singularities which should be regulated to allow for a successful evaluation. Solution method: Complex masses can be used in the loop integrals to stand for a width of an unstable particle, regulating the singularities by moving the poles away from the real axis. Reasons for new version: The previous version was restricted to massless particles in the loop. Summary of revisions: Real and complex masses are supported, a general mu parameter for the renormalization scale is introduced, improvements in the caching system and the user interface. Running time: Depends on the nature of the problem. A single call to a rank 6 six-point form factor at a randomly chosen kinematic point, using complex masses, takes 0.06 seconds on an Intel Core 2 Q9450 2.66 GHz processor.

Keyword:

NLO computations

One-loop diagrams

Complex masses

Unstable particles