specific diagram cross section

Dear Justin,

Let me first stress that the computation of
g g > t t~ h /g is not gauge invariant and therefore our computation is not lorentz invariant.
as you can check by doing “check g g > t t~ h /g”

> Note That all width have been set to zero for those checks
>
> Lorentz invariance results:
> Process Min element Max element Relative diff. Result
> g g > t t~ h 1.5556866770e-06 3.6067932638e-06 5.6867872284e-01 Failed
> JAMP 0 5.3695502611e-05 1.0735347556e-04 4.9982520518e-01 Failed
> JAMP 1 2.3141690482e-05 5.9012399664e-05 6.0785037358e-01 Failed
> Summary: 0/1 passed, 1/1 failed
> Failed processes: g g > t t~ h
> Gauge results:
> Process matrix BRS ratio Result
> g g > t t~ h 1.3058852907e-05 1.8038771812e-05 1.3813442834e+00 Failed
> JAMP 0 3.5788588231e-04 3.8482713198e-04 1.0752788836e+00 Failed
> JAMP 1 2.9012103489e-04 3.8482713198e-04 1.3264365065e+00 Failed
> Summary: 0/1 passed, 1/1 failed
> Failed processes: g g > t t~ h
> Gauge results (switching between Unitary/Feynman):
> Process Unitary Feynman Relative diff. Result
> g g > t t~ h 1.4779590412e-05 1.4779590412e-05 0.0000000000e+00 Passed
> Summary: 1/1 passed, 0/1 failed
> Process permutation results:
> Process Min element Max element Relative diff. Result
> g g > t t~ h 2.1804293521e-06 2.1804293521e-06 1.9423535700e-16 Passed
> Summary: 1/1 passed, 0/1 failed

Therefore all the number that you can get from those result are meaningless if you do not include the rest of the computation (the two other diagram and the associated interference) with the same choice of gauge and the same scale choice. If you do such computation in partial way, I would strongly suggest that you do not use our default dynamical scale choice but either a fix scale or a pure kinematical one (like HT divided by two)

> I am trying to compute the cross sections of these two 'styles' of diagrams separately so that I can compare them, but I don't know how to exclude (or only build) the diagrams I want. I have tried two separate processes like ‘ g g > t t~ /g, t > t h ' and similarly ' g g > t t~ /g, t~ > t~ h ', which individually produce two of the four diagrams, but this would mean my cross-sections are not just simply summing the two cross-sections (right?), so this isn't particularly helpful.

Those kind of computation are not gauge invariant. So I do not see how you can learn anything physical by splitting such computation.

> I know in another post it was suggested that a user simply edit their matrix.f file. If this is the case, is it as simple as commenting out ALL references to, say, diagrams 1 and 3, or if there was more of an art to it than that? Alternatively, if there is a different way to do this all from the console, I’d like to try that too.

We do not have any console for this. The main reason is that we want to discourage people to try such type of non-physical computation with our code.
Now if you really know what you are doing, then yes the way to go is to edit the matrix.f files.
I really do not see how to make such computation coherent so it is everything but clear to me how to modify matrix.f in a consistent way.

Cheers,

Olivier

> On Jul 7, 2016, at 16:57, Justin <email address hidden> wrote:
>
> New question #296114 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/296114
>
> Hi,
>
> Hopefully I'm using all the terminology correctly, as I am a complete amateur. The process I am looking at is: ' g g > t t~ h /g ' Out of this, I get 6 diagrams, 2 of which show the g > t t~ decay and then t t~ fusion to higgs, and the other 4 which depict a higgs coming off one of the t or t~.
>
> I am trying to compute the cross sections of these two 'styles' of diagrams separately so that I can compare them, but I don't know how to exclude (or only build) the diagrams I want. I have tried two separate processes like ' g g > t t~ /g, t > t h ' and similarly ' g g > t t~ /g, t~ > t~ h ', which individually produce two of the four diagrams, but this would mean my cross-sections are not just simply summing the two cross-sections (right?), so this isn't particularly helpful.
>
> I know in another post it was suggested that a user simply edit their matrix.f file. If this is the case, is it as simple as commenting out ALL references to, say, diagrams 1 and 3, or if there was more of an art to it than that? Alternatively, if there is a different way to do this all from the console, I'd like to try that too.
>
> Thanks,
>
> Justin
>
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