RECOLA2: REcursive Computation of One-Loop Amplitudes 2

Abstract

We present the Fortran95 program Recola2 for the perturbative computation of next-to-leading-order transition amplitudes in the Standard Model of particle physics and extended Higgs sectors. New theories are implemented via model files in the ’t Hooft–Feynman gauge in the conventional formulation of quantum field theory and in the Background-Field method. The present version includes model files for Two-Higgs-Doublet Model and the Higgs-Singlet Extension of the Standard Model. We support standard renormalization schemes for the Standard Model as well as many commonly used renormalization schemes in extended Higgs sectors. Within these models the computation of next-to-leading-order polarized amplitudes and squared amplitudes, optionally summed over spin and colour, is fully automated for any process. Recola2 allows the computation of colour- and spin-correlated leading-order squared amplitudes that are needed in the dipole subtraction formalism. Recola2 is publicly available for download at http://recola.hepforge.org. Program summaryProgram Title:Recola2Program Files doi:http://dx.doi.org/10.17632/sn4wvmkd9k.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 theories.Solution 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 9 external particles at one-loop level and up to 10 external particles at tree level. For large multiplicities available internal storage may cause limitations. Presently besides the Standard Model, the Two-Higgs-Doublet Model and the Higgs-singlet extension of the Standard Model are supported.