One-loop provider

A one-loop provider (or one-loop program) is a specialised software for generating one-loop amplitudes for perturbative quantum field theory calculations. They are a special case of external amplitude providers. One-loop amplitudes contribute to next-to-leading order (and higher order) cross sections as well as the leading-order cross sections of loop-induced processes. Most one-loop providers can also compute other amplitudes, but their strength lies in loop amplitudes, which are typically much harder to compute than tree-level amplitudes.

One-loop providers are often used as external software to provide one-loop amplitudes for event generators.

List of one-loop providers

• OpenLoops
• GoSam
• MadGraph5_aMC@NLO
• VBFNLO

Use from other software

The following event generators use or support the use of external one-loop providers:

• Herwig 7
• Sherpa