[QCD] vs [noborn=QCD] vs [noborn=QED] vs [virt=QCD]

Asked by Yingjie Wei on 2021-04-27

Hi:

    I am quite new to Madgraph. Could I just ask a naive question? (I couldn't find an answer anywhere)

    I saw people often use the command like: `generate g g > z z ` followed by "[ noborn=QCD ]" or "[virt=QCD]" or "[QCD]" or "[noborn=QED]", what's the exact meaning of the "[ noborn=QCD ]", "[virt=QCD]", "[QCD]" or "[noborn=QED]"?

    Or is there a user manual of Madgraph where I could find this information?

Thanks so much,
Yingjie Wei

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hi,

 - [virt=...] allows to generate only standalone code no phase-space generation.
 - [noborn=...] means that you claim that the process does not have any tree-level amplitude. Which allows to use loop-induced mode (note that we do not check if a tree-level exists and result are likely non physical if a tree level amplitude does exists)

The difference between [...=QCD] and [...=QED] or [...=QCD QED]are the type of particles that can be present within the loop. QCD allows only QCD particles within the loop (quark and gluon) while QED will allow electroweak loop (W,Z,photon,...)

Reference for loop induced process is 1507.00020 <https://arxiv.org/abs/1507.00020>

Cheers,

Olivier
> On 27 Apr 2021, at 09:50, Yingjie Wei <email address hidden> wrote:
>
> New question #696778 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/696778
>
> Hi:
>
> I am quite new to Madgraph. Could I just ask a naive question? (I couldn't find an answer anywhere)
>
> I saw people often use the command like: `generate g g > z z ` followed by "[ noborn=QCD ]" or "[virt=QCD]" or "[QCD]" or "[noborn=QED]", what's the exact meaning of the "[ noborn=QCD ]", "[virt=QCD]", "[QCD]" or "[noborn=QED]"?
>
> Or is there a user manual of Madgraph where I could find this information?
>
> Thanks so much,
> Yingjie Wei
>
>
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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