Recola2: REcursive Computation of One-Loop Amplitudes 2
Ansgar Denner, Jean-Nicolas Lang, Sandro Uccirati
TL;DR
Recola2 extends automated one-loop amplitude calculations to the Standard Model and beyond, introducing support for extended Higgs sectors (2HDM and HSESM) via UFO-derived model files and renormalization schemes. It integrates with the Collier tensor-integral library and offers both Fortran95 and C++ interfaces, plus a Python interface, with Backgound-Field Method support for cross-checks. The framework provides comprehensive input and process-management subroutines, MSbar-scale handling, and color/spin-correlated squared amplitudes needed for dipole subtraction, enabling flexible, automated NLO predictions in BSM theories. Its installation options, detailed conventions, and demo programs facilitate adoption for precise phenomenology in extended Higgs sectors and potential future extensions.
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 the 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.