MadGraph5_aMC@NLO

renormalization scale

Asked by IvanSobolev

Dear MadTeam,

Is it possible to tune the content of "setscale.f" file which is generated automatically when I use "output" command? More precisely, I have a set of processes with a jet in the final state (which is always the 3rd particle). And I want "rscale" variable always to be equal to transverse momentum of jet. So, I want my "setscale.f" file to include the following strings:

       elseif(dynamical_scale_choice.eq.0) then
          rscale=dsqrt(P(1,3)*P(1,3)+P(2,3)*P(2,3))

instead of default ones. Can MG do it automatically?

Best,
Ivan

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Olivier Mattelaer
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Best Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi Ivan,

Sure you can use the Plugin mode to automatically ensure that behaviour.
https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/Plugin

Cheers,

Olivier

> On 26 Mar 2017, at 13:10, IvanSobolev <email address hidden> wrote:
>
> New question #592338 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/592338
>
> Dear MadTeam,
>
> Is it possible to tune the content of "setscale.f" file which is generated automatically when I use "output" command? More precisely, I have a set of processes with a jet in the final state (which is always the 3rd particle). And I want "rscale" variable always to be equal to transverse momentum of jet. So, I want my "setscale.f" file to include the following strings:
>
> elseif(dynamical_scale_choice.eq.0) then
> rscale=dsqrt(P(1,3)*P(1,3)+P(2,3)*P(2,3))
>
> instead of default ones. Can MG do it automatically?
>
> Best,
> Ivan
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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IvanSobolev (sobolev-ivan) said : 		#2

Dear Olivier,

Many thanks for your help!
Nevertheless I solved my problem in a bit different way. Probably it will be helpful for everybody who will face the same question.
The solution is quiete easy. When you use "output" command, MG just makes copy of everything that is contained in /MG5_aMC_v2_3_3/Template/LO directory. So all you need is just to modify "/MG5_aMC_v2_3_3/Template/LO/SubProcesses/setscales.f" file in a way you need.

Best,
Ivan

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IvanSobolev (sobolev-ivan) said : 		#3

Thanks Olivier Mattelaer, that solved my question.

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Stefano Frixione (stefano-frixione) said : 		#4

Ivan,
of course that is a possibility, which works both at the LO and at the NLO.

However, it is a very dangerous one, and it must be deprecated.

The reason is that, all changes made in the Template subdirectories will apply to *all* the processes
subsequently generated. A more correct way to proceed is that of first outputting the process
you're interested into, quit the interface, edit setscales.f in the relevant process directory, and
afterwards resume the run. Thus, all modifications will apply only to the current process, but not
to those generated in the future.

If one wants to modify setscales.f in Template, the way to do it is to add another option (identified
by the integer dynamical_scale_choice).

Best, Stefano