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Enable/Fix scale variations for loop generators that do not provide pole coefficients

Marek Schoenherr requested to merge tmp-recola-scalevar-fix into rel-2-2-8

Enable/Fix scale variations for loop generators that do not provide pole coefficients phase-space-point-by-phase-space-point. (Applicable to 2.2.8)

Currently, the muR coefficient for the scale variations sums the IR pole coefficients of V and I and adds the UV renormalisation term coefficient. This is done in order to have the right coefficients in all cases, irrespective of whether VI are calculated together or only V or I is calculated. Some OLP (eg. Recola), however, do not provide the pole coefficient on a phase-space-point-by-phase-space-point level and thus end up with an incorrect scale variation for anything including V. In particular, when the combination of VI is part of NLO calculation, the NLO scale variation is wrong. This MR implements two options:

  1. Loop ME interfaces themselves set their defaults on whether pole coefficients are provided.

  2. NLO_MUR_COEFFICIENT_FROM_VIRTUAL=<0|1> allows to select by hand whether the IR pole coefficients should be part of the scale variation. (default: 1)

If either of the above yields false, IR pole cancellation is assumed and, thus, only the UV renormalisation term pole coefficient is considered in the scale variation.

Edited by Frank Siegert

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