News from FormCalc and LoopTools

TL;DR

FormCalc and LoopTools address the challenge of efficient, stable computation of Feynman amplitudes at one loop. The paper presents Version 5 of FormCalc, with iterative phase-space generation, PDF/Photon convolution, and modular code architecture, together with Version 2.2 of LoopTools, featuring five-point functions, a unified two-point function, complex and alternate versions, and enhanced accuracy. The contributions improve numerical stability (e.g., Denner-Dittmaier decomposition), performance (caching and LU-based reductions), and flexibility (runtime version selection, CLI, and quadruple-precision builds). The tools are open-source under the LGPL and empower phenomenological calculations with interfaces across Fortran, C/C++, Mathematica, and PDF/IDE ecosystems, enabling robust and reusable workflows for loop-level computations.

Abstract

The FormCalc package automates the computation of FeynArts amplitudes up to one loop including the generation of a Fortran code for the numerical evaluation of the squared matrix element. Major new or enhanced features in Version 5 are: iterative build-up of essentially arbitrary phase-spaces including cuts, convolution with density functions, and uniform treatment of kinematical variables. The LoopTools library supplies the one-loop integrals necessary for evaluating the squared matrix element. Its most significant extensions in Version 2.2 are the five-point family of integrals, and complex and alternate versions.