openloops is hosted by Hepforge, IPPP Durham


A dedicated OpenLoops 2 publication and documentation will be released soon. Here we list the changes most relevant for (Sherpa) users.

New in OpenLoops 2

  • Thanks to the in-house OpenLoops on-the-fly reduction combined with a versatile hyprid precision mode the stability system in OpenLoops 2 has been significantly improved. Settings and presets of the stability system in OpenLoops 1 are now deprecated (preset, stability_mode, redlib1, redlib2 etc.).
  • Support of NLO QCD and NLO EW corrections in the full SM.
  • Some libraries were merged, i.e. individual libraries may not exist anymore under the same name (check process repository list for more information); download will automatically point to the new libs. If the allowed_libs option is used, make sure, the library specified still exists/is updated.
  • The default EW input scheme has been changed to the Gmu-scheme (before in OpenLoops 1: alpha(MZ) scheme). Note: in current Sherpa versions the CHECK_BORN might fail due to this change, as the EW input scheme is not automatically adjusted. In practice Sherpa only uses the QCD K-factor V/B obtained from OpenLoops, where the EW coupling alpha cancels out. Nevertheless it is desirable to specify the alpha(MZ) input scheme in Sherpa runcards via OL_PARAMETERS ew_scheme 2.
  • For external photons a mixed input scheme is used. At tree-level and NLO QCD this corresponds to a rescaling by alpha(0)/alpha for each external photon.