Running alpha-s

[kilian]

alpha-s depends on the process energy scale. W2 should support this effect. Particularly important for LHC processes.

[kilian]

There are two issues:

1) The WHIZARD part is simple. Either give alpha-s as an extra parameter to new_event, or call a new interface routine update_alpha_s which has to be provided within the process code (has to be written by targets.ml, but this is trivial). I would prefer the latter.

2) This interface routine should call a corresponding routine within parameters_XXX.f90. Here comes the physics part. The writer of the model has to decide which parameters depend on the event energy scale (via alpha_s) and which do not. In particular, in the MSSM, gluino couplings should not depend on scale but quartic gluon-W-squark-squark couplings should. What about the Hgg coupling? So the update routine should be explicitly written for each model. It may also be called internally when executing import_from_whizard in order to not duplicate code.

[Juergen Reuter]

This can be done in the model files (and will be, basically for the MSSM etc. it is already there). First, it has to be settled how to handle this from a technical point of view!

[kilian]

The WHIZARD and O'Mega part is done [1453].

The remaining task is to implement a subroutine model_update_alpha_s in each of the parameters.XXX.f90 source code files. After this is done, the corresponding call can be activated (comment sign removed) in targets.ml.

The subroutine parallels import_from_whizard. The interface is

subroutine model_update_alpha_s (alpha_s)
  real(default), intent(in) :: alpha_s
end subroutine model_update_alpha_s

In models without alpha-s, this should be a no-op, of course.

[Juergen Reuter]

I implemented the subroutines model_update_alpha_s for the models QED, QCD, and SM in [1498]. WK, could you check please, that this is as intended!?

[Juergen Reuter]

This is now implemented for all models in [r1509]. Testing is not possible right now because of ticket #132. What is missing is the implementation of the possibility to run also the running alpha_s from LHAPDF.

[Juergen Reuter]

In [r1510] I implemented the corresponding subroutines in all models, also the option for using alpha_s from LHAPDF. I furthermore added an as yet incomplete self-test, which right now fails anyhow because of Ticket #132. Nevertheless, I close the ticket and merge the testing with the general validation ticket #88.

[Juergen Reuter]

Milestone v2.0.0final deleted