error: split amp are not supported for spin2 and 3/2

Hi,

You should be able to set the run_card parameter
hel_recycling to False in the run_card.
or just turn off split_amp (which is included in the above flag) by setting
hel_splitamp to False.
(None of those parameters are visible by default in the run_card but you can add them
(more information on those parameters here: https://arxiv.org/pdf/2102.00773.pdf)

Could you attach your UFO model
(or send it to me at <email address hidden>) and then I will look why such splitting does not work in this case.

Cheers,

Olivier

Thank you Olivier, adding "False = hel_splitamp" in my run_card allowed MG to run. I'll send you the UFO model via email.

The issue is resolved.

Nikita

So the issue is that this optimization of MG5aMC assumes that the name of the lorentz structure is based on the spin type of the particles.
You do you have one for which this is not the case (FF1).
if you change that name to FFVFF1 then this fix the problem.

This is indeed an issue of that optimizer and I might try to use a more secure version to get the spin of each interaction if this occurs too often. But for the moment I will just close the bug report.

Thanks a lot for the model, this is very usefull.

Cheers,

Olivier

great to know! and happy to contribute to fixing a bug!

On Thu, Feb 17, 2022 at 7:06 AM Olivier Mattelaer <
<email address hidden>> wrote:

> So the issue is that this optimization of MG5aMC assumes that the name of
> the lorentz structure is based on the spin type of the particles.
> You do you have one for which this is not the case (FF1).
> if you change that name to FFVFF1 then this fix the problem.
>
> This is indeed an issue of that optimizer and I might try to use a more
> secure version to get the spin of each interaction if this occurs too
> often. But for the moment I will just close the bug report.
>
> Thanks a lot for the model, this is very usefull.
>
> Cheers,
>
> Olivier
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1960966
>
> Title:
> error: split amp are not supported for spin2 and 3/2
>
> Status in MadGraph5_aMC@NLO:
> New
>
> Bug description:
> Hi everyone,
>
> I encountered "Exception : split amp are not supported for spin2 and 3/"
> when trying to simulate a simple tree-level process
> involving a variation of scalar QED (the process is pi+ N > p+ N A',
> where A' is a dark photon). Madgraph (v3_1_1) correctly generates the
> bremsstrahlung diagrams (which involve a four-point vertex that A A' pi+
> pi- in addition to the cubic ones). If I manually turn off the
> contribution of this quartic vertex (via a param_card parameter) the event
> generation works; other processes involving the same vertex (e.g. pi+ A >
> pi+ A') also work without any issues.
>
> Any ideas of what might be happening?
>
> Thanks!
>
> PS. The full log is attached
>
> To manage notifications about this bug go to:
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>
>