R E C O L A—REcursive Computation of One-Loop Amplitudes

Abstract

We present the Fortran95 program Recola for the perturbative computation of next-to-leading-order transition amplitudes in the Standard Model of particle physics. The code provides numerical results in the ’t Hooft–Feynman gauge. It uses the complex-mass scheme and allows for a consistent isolation of resonant contributions. Dimensional regularization is employed for ultraviolet and infrared singularities, with the alternative possibility of treating collinear and soft singularities in mass regularization. Recola supports various renormalization schemes for the electromagnetic and a dynamical Nf-flavour scheme for the strong coupling constant. The calculation of next-to-leading-order squared amplitudes, summed over spin and colour, is supported as well as the computation of colour- and spin-correlated leading-order squared amplitudes needed in the dipole subtraction formalism. Program summaryProgram Title:RecolaProgram Files doi:http://dx.doi.org/10.17632/mtzkz47y8r.1Licensing provisions: GNU GPL version 3Programming language:Fortran95Nature of problem: Evaluation of general tree-level and one-loop scattering amplitudes occurring in the calculation of observables in relativistic quantum field theoriesSolution method: Tree-level and one-loop amplitudes are numerically calculated using a recursive algorithm. For one-loop amplitudes numerical results for tensor integrals are needed as input. These are provided by the Collier library. In addition, contributions of counterterms and rational terms are determined via dedicated Feynman rules.Restrictions: The code has been used for processes with up to 7 external particles at one-loop level and up to 9 external particles at tree level. For large multiplicities available internal storage may cause limitations.External routines/libraries:Collier library