ParametersHere you find a list of parameters available in OpenLoops 2. Within the general purpose Monte Carlo frameworks (e.g. Sherpa or Herwig++) these parameters are synchronised automatically. A more detailed documentation will soon be available. Model parameters
OpenLoops allows the choice between three EW input schmemes, which can be selected via the parameter ew_scheme according to the following table.
Unstable particles with a finite width are by default treated in the complex mass scheme, i.e. M^{2} = rM^{2}-i rM*Γ. Here rM and Γ are the real valued on-shell mass and width of the unstable particle. The cosine of the weak mixing angle c_{W} is always defined as c_{W}=M_{W}/M_{Z} and thus in general a complex valued parameter. The chosen EW input scheme also fixes the EW renormalisation scheme. By default all quark flavours are included at one-loop. More precisely, the number of quark flavours that contribute to the renormalisation (and evolution) of α_{s} is chosen as max(number of massless quarks, minnf_alphasrun). Thus, by default only massless quarks are treated as active flavours, while the contribution of massive quarks is effectively decoupled from the running of α_{s} by renormalising it via zero-momentum subtraction. In this approach, above threshold the heavy-quark (with mass Mq) contributions to any renormalised one-loop amplitudes generate logarithms of μ_{R}/Mq that are not present in the evolution of α_{s} above threshold. This behaviour can be altered specifying the parameter minnf_alphasrun. If set to a value larger then the number of massless quark flavours, also the corresponding heavy quarks are assumed to contribute to the running of the strong coupling (above the respective thresholds). Process parameters
These order_ew, and order_qcd selectors are used for the bookkeping of different perturbative orders as explained here. Technical parameters
Further technical parameters affecting the stability system are listed here. |