Tools for NLO automation: Extension of the golem95C integral library

Abstract

We present an extension of the program golem95C for the numerical evaluation of scalar integrals and tensor form factors entering the calculation of one-loop amplitudes, which supports tensor ranks exceeding the number of propagators. This extension allows various applications in Beyond the Standard Model physics and effective theories, for example higher ranks due to propagators of spin two particles, or due to effective vertices. Complex masses are also supported. The program is not restricted to the Feynman diagrammatic approach, as it also contains routines to interface to unitarity-inspired numerical reconstruction of the integrand at the tensorial level. Therefore, it can serve as a general integral library in automated programs to calculate one-loop amplitudes. New version program summaryProgram title: golem95-1.3.0Catalogue identifier: AEEO_v3_0Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEEO_v3_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 242036No. of bytes in distributed program, including test data, etc.: 1092837Distribution format: tar.gzProgramming language: Fortran95.Computer: any computer with a Fortran95 compiler.Operating system: Linux, Unix.RAM: RAM used per integral/form factor is insignificantClassification: 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_v2_0Journal reference of previous version: Comput. Phys. Comm. 182(2011)2276Does the new version supercede the previous version?: yesNature of problem:evaluation of one-loop multi-leg integrals occurring in the calculation of next-to-leading order corrections to scattering amplitudes in particle physics. In the presence of particles with spin two in the loop, or effective vertices, or certain gauges, tensor integrals where the rank exceeds the number of propagators N are required.Solution method:extension of the reduction algorithm to rank r≤10 for N≤4 and r≤N+1 for N≥5, which is sufficient for most applications in Beyond the Standard Model Physics.Reasons for new version:the previous version was restricted to tensor ranks less than or equal to the number of propagators.Summary of revisions:tensor ranks >N are supported, an alternative reduction method for the case of infrared divergent triangles is implemented, numerical stability for the case of small mass differences has been improved.Running time:depends on the nature of the problem. A single call to a rank 6 five-point form factor at a randomly chosen kinematic point, using real masses, takes 10−3 s on an Intel Core 4 i7-3770 CPU with a 3.4 GHz processor.