COLLIER -- A fortran-library for one-loop integrals

TL;DR

COLLIER is a Fortran library designed for the stable numerical evaluation of one-loop integrals in quantum field theories, supporting complex masses and multiple regularization schemes, useful for NLO calculations.

Contribution

It introduces a new Fortran library with advanced methods for numerical stability and flexibility in regularization, supporting up to six-point functions in one-loop integrals.

Findings

Supports N=6 point functions in one-loop integrals.

Achieves numerical stability for 3- and 4-point tensor integrals.

Successfully tested in various NLO QCD and EW calculations.

Abstract

We introduce the fortran-library COLLIER for the numerical evaluation of one-loop scalar and tensor integrals in perturbative relativistic quantum field theories. Important features are the implementation of dedicated methods to achieve numerical stability for 3- and 4-point tensor integrals, the support of complex masses for internal particles, and the possibility to choose between dimensional and mass regularization for infrared singularities. COLLIER supports one-loop N-point functions up to currently N=6 and has been tested in various NLO QCD and EW calculations.