Caravel: A C++ framework for the computation of multi-loop amplitudes with numerical unitarity

S Abreu,J Dormans,F Febres Cordero,H Ita,M Kraus,B Page,E Pascual,M.S Ruf,V Sotnikov

doi:10.1016/j.cpc.2021.108069

Abstract

We present the first public version of Caravel, a C++17 framework for the computation of multi-loop scattering amplitudes in quantum field theory, based on the numerical unitarity method. Caravel is composed of modules for the D-dimensional decomposition of integrands of scattering amplitudes into master and surface terms, the computation of tree-level amplitudes in floating point or finite-field arithmetic, the numerical computation of one- and two-loop amplitudes in QCD and Einstein gravity, and functional reconstruction tools. We provide programs that showcase Caravel's main functionalities and allow to compute selected one- and two-loop amplitudes. Program summaryProgram Title:CaravelCPC Library link to program files:https://doi.org/10.17632/rfjrxrb3rk.1Developer's repository link:https://gitlab.com/caravel-public/caravel.gitLicensing provisions: GPLv3Programming language: C++External dependencies:• Required:Python3 [1], meson [2]• Optional:Doxygen [3], Eigen [4], GiNaC [5], GMP [6], Lapack [7], MPFR [8], MPI [9], PentagonLibrary [10,11], QD [12]Nature of problem: The computation of multi-loop multi-particle scattering amplitudes in quantum field theorySolution method: The multi-loop numerical unitarity method, functional reconstruction algorithmsAdditional comments including restrictions and unusual features: Current version includes tools employed in previous calculations, with the aim of showcasing details of the algorithms employed. Computations are organized by provided data files.

Highlights

We present the first public version of Caravel, a C++17 framework for the computation of multi-loop scattering amplitudes in quantum field theory, based on the numerical unitarity method
Was. ✩✩ This paper and its associated computer program are available via the Computer Physics Communications homepage on ScienceDirect
The corresponding free parameters are numerically computed at each phase-space point by constructing systems of linear equations in which the parameters are the unknowns and the numerical entries are associated to products of tree-level amplitudes

Summary

Introduction

We present the first public version of Caravel, a C++17 framework for the computation of multi-loop scattering amplitudes in quantum field theory, based on the numerical unitarity method. The current release of Caravel includes a module for computing products of tree-level amplitudes in several theories through off-shell recursion relations [28], and tools that allow the efficient construction and solution of the systems of linear equations that determine the integrand. Whilst these components work for generic multi-loop amplitudes, other components such as the construction of the parametrization are required as input. In this release we showcase the different available tools by providing a series of example programs. Appendix A and Appendix B contain technical details about our conventions for color-ordered helicity amplitudes and phasespace parametrizations

Objectives

Methods

Conclusion