RECOLA: REcursive Computation of One-Loop Amplitudes

TL;DR

Recola introduces a Fortran95 library for automated tree-level and one-loop SM amplitudes with a focus on electroweak corrections, using a recursive off-shell current framework and interfacing with Collier for tensor integrals. It supports dimensional and mass regularization, multiple EW and QCD renormalization schemes (including complex-mass and G_F/α schemes), and provides Born and loop squared amplitudes along with colour- and spin-correlated quantities essential for dipole subtraction. The paper details installation, usage, and a comprehensive set of subroutines enabling dynamic parameter control, process definition, and on-the-fly computation, along with rigorous cross-checks against Pole and OpenLoops. Recola's design aims for fast, on-demand NLO predictions with flexible resonance selection, broad SM applicability, and compatibility with standard subtraction formalisms. The work underscores a significant step toward automated, high-precision SM calculations with extensive validation and clear pathways for extension to broader theories.

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.