how to specifiy the mediator of a process

Asked by Steven Jeremies on 2021-05-26

Hi everyone,

I generated the process u b > d t which yielded the correct diagram as the output. I tried to specify the input by typing

>> generate u b > w+ > d t

just to try out the syntax for a more complex diagram later in which I want to separate the contributing diagrams . I thought this second input should give the same result as the one above without the specification. However, I get the "NoDiagramException: No amplitudes generated from process" error.
Why is that?

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MadGraph5_aMC@NLO Edit question
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Solved by:
Olivier Mattelaer
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Best Olivier Mattelaer (olivier-mattelaer) said :
#1

The syntax > A >
requires that the particle A appears at least once in S-channel
so this is not the syntax that you want.

We do not have any equivalent syntax for T-channel.

The syntax > A > is already strongly discouraged can often leads to unphyiscal result.
Providing an eauivalent for T-channel will be a nightmare in that direction.
If you really need such type of filtering you have to code it yourself (and at your own risk) via the diagram filtering method: https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FAQ-General-15

Cheers,

Olivier

> On 26 May 2021, at 11:35, Steven Jeremies <email address hidden> wrote:
>
>>> generate u b > w+ > d t

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Steven Jeremies (minits) said :
#2

Thanks Olivier Mattelaer, that solved my question.