# OpenLoops 2

## TL;DR

OpenLoops 2 introduces a comprehensive extension of the original algorithm to include the full Standard Model, with new features for electroweak corrections, improved stability, and faster computations for complex particle physics processes.

## Contribution

It extends OpenLoops to the full Standard Model, incorporating electroweak corrections and a new on-the-fly reduction algorithm for enhanced speed and stability.

## Key findings

- Significant speed improvements for multi-leg calculations
- Enhanced numerical stability with hybrid-precision methods
- Successful implementation of electroweak corrections in automated amplitudes

## Abstract

We present the new version of OpenLoops, an automated generator of tree and one-loop scattering amplitudes based on the open-loop recursion. One main novelty of OpenLoops 2 is the extension of the original algorithm from NLO QCD to the full Standard Model, including electroweak (EW) corrections from gauge, Higgs and Yukawa interactions. In this context, among several new features, we discuss the systematic bookkeeping of QCD-EW interferences, a flexible implementation of the complex-mass scheme for processes with on-shell and off-shell unstable particles, a special treatment of on-shell and off-shell external photons, and efficient scale variations. The other main novelty is the implementation of the recently proposed on-the-fly reduction algorithm, which supersedes the usage of external reduction libraries for the calculation of tree-loop interferences. This new algorithm is equipped with an automated system that avoids Gram-determinant instabilities through analytic methods in combination with a new hybrid-precision approach based on a highly targeted usage of quadruple precision with minimal CPU overhead. The resulting significant speed and stability improvements are especially relevant for challenging NLO multi-leg calculations and for NNLO applications.