NP number selection and Incompatibility of "Model HEL_UFO" with "Model SM" in terms of Feynman Diagrams

Asked by volkan cetinkaya on 2017-10-24

Dear Olivier Mattelaer,
Dear Valentin Hirschi,

My questions are below:

1- I use the Model HEL_UFO in my accounts. For example, when I select HEL_UFO as an import model for "e- e+ > h z" process, I obtain 6 Feynman diagrams (this also means NP = 0, because it gives the same result when I write "e- e+ > h z NP=0"). 3 of these 6 diagrams are fundamentally different from each other, but why are 1 to 2, 3 to 4 and 5 to 6 are exactly the same? When I select sm as the import model (or when I choose nothing) for same process, I get a single diagram that is the same as the first of the six diagrams above. Is there any discrepancy between model sm and model HEL_UFO in this case?

2- I want to take into account only the NP = 1 (only signal) for both "e- e+ > h z" process and decay of h and z. The process I wrote for this and the error I get is as follows:

MG5_aMC>generate e- e+ > h z WEIGHTED==5
INFO: Trying process: e- e+ > h z NP<=1 WEIGHTED==5 @1
INFO: Process has 16 diagrams
1 processes with 16 diagrams generated in 0.030 s
Total: 1 processes with 16 diagrams

...it is ok. But below:

MG5_aMC>generate e- e+ > h z WEIGHTED==5, h > j j, z > mu- mu+
Error detected in "generate e- e+ > h z WEIGHTED==5, h > j j, z > mu- mu+"
write debug file MG5_debug
MadGraph5Error : Decay processes cannot specify squared orders constraints.

(At the same time, "new physics vertice" must come in the decays of h and z).

Best regards,

Volkan Çetinkaya.

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2017-10-24
2017-10-24
 Olivier Mattelaer (olivier-mattelaer) said on 2017-10-24: #1

Hi,

I’m not an expert in the HEL_UFO model and therefore I would suggest to contact the author of that model for some more detailed explanation.

> 1- I use the Model HEL_UFO in my accounts. For example, when I select HEL_UFO as an import model for “e- e+ > h
> z" process, I obtain 6 Feynman diagrams (this also means NP = 0, because it gives the same result when I write "e- e+ > h z NP=0"). 3 of these 6 diagrams are fundamentally different from each other, but why are 1 to 2, 3 to 4 and 5 to 6 are exactly the same? When I select sm as the import model (or when I choose nothing) for same process, I get a single diagram that is the same as the first of the six diagrams above. Is there any discrepancy between model sm and model HEL_UFO in this case?

The “sm” model assumes that the lepton are massless and therefore that they do not couple to the Higgs.
The HEL_UFO does not seems to make such assumptions and therefore has additional diagram.

For the duplication of the Feynman Diagram, they are actually different diagram but their graphical representation is actually identical.
The author of the model have implemented two interactions for the e+e-z:

V_1026 = Vertex(name = 'V_1026',
particles = [ P.e__plus__, P.e__minus__, P.Z ],
color = [ '1' ],
lorentz = [ L.FFV1, L.FFV2, L.FFV3, L.FFV5, L.FFV7, L.FFV8 ],
couplings = {(0,0):C.GC_893,(0,3):C.GC_1791,(0,2):C.GC_2022,(0,5):C.GC_2022,(0,1):C.GC_2023,(0,4):C.GC_2023})

V_1027 = Vertex(name = 'V_1027',
particles = [ P.e__plus__, P.e__minus__, P.Z ],
color = [ '1' ],
lorentz = [ L.FFV1, L.FFV5 ],
couplings = {(0,0):C.GC_1793,(0,1):C.GC_887})

The second one seems to be the SM one, while the first one has also a contribution consider like “QED”.
If I remember correctly the paper, this was linked to some renormalization of some operator.
But as I said above, you should contact the author (or read their paper to understand what this is)

> MG5_aMC>generate e- e+ > h z WEIGHTED==5, h > j j, z > mu- mu+
> Error detected in "generate e- e+ > h z WEIGHTED==5, h > j j, z > mu- mu+"
> write debug file MG5_debug
> MadGraph5Error : Decay processes cannot specify squared orders constraints.

You can not use “==“ or “>” operator for the ordering in presence of decay-chain syntax.
Actually in this case, we should be able to do the computation, but the crash is more linked to an implementation error
than a real lack of possibility to do such computation.

They are no simple solution here, the easiest one is to implement a diagram filtering:

Cheers,

Olivier

> On Oct 24, 2017, at 11:13, volkan cetinkaya <email address hidden> wrote:
>
> New question #659849 on MadDM:
>
> Dear Olivier Mattelaer,
> Dear Valentin Hirschi,
>
> My questions are below:
>
> 1- I use the Model HEL_UFO in my accounts. For example, when I select HEL_UFO as an import model for "e- e+ > h z" process, I obtain 6 Feynman diagrams (this also means NP = 0, because it gives the same result when I write "e- e+ > h z NP=0"). 3 of these 6 diagrams are fundamentally different from each other, but why are 1 to 2, 3 to 4 and 5 to 6 are exactly the same? When I select sm as the import model (or when I choose nothing) for same process, I get a single diagram that is the same as the first of the six diagrams above. Is there any discrepancy between model sm and model HEL_UFO in this case?
>
> 2- I want to take into account only the NP = 1 (only signal) for both "e- e+ > h z" process and decay of h and z. The process I wrote for this and the error I get is as follows:
>
> MG5_aMC>generate e- e+ > h z WEIGHTED==5
> INFO: Trying process: e- e+ > h z NP<=1 WEIGHTED==5 @1
> INFO: Process has 16 diagrams
> 1 processes with 16 diagrams generated in 0.030 s
> Total: 1 processes with 16 diagrams
>
> ...it is ok. But below:
>
>
> MG5_aMC>generate e- e+ > h z WEIGHTED==5, h > j j, z > mu- mu+
> Error detected in "generate e- e+ > h z WEIGHTED==5, h > j j, z > mu- mu+"
> write debug file MG5_debug
> MadGraph5Error : Decay processes cannot specify squared orders constraints.
>
> (At the same time, "new physics vertice" must come in the decays of h and z).
>
>
> Best regards,
>
> Volkan Çetinkaya.
>
>
>
>
>
>
>
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