MadSpin error for BSM Physics

Hi,

I do not think that MadSpin was ever tested/validated for 1>N production.
Also decay of tau is problematic since the width is so small that the code is numerically unstable.
We do have special handling within madevent for that but not within madspin.

In this case (or in general for tau decay) taoula is likely the best option.

Cheers,

Olivier

> On 9 Jun 2021, at 12:45, Marco H. <email address hidden> wrote:
>
> New question #697460 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/697460
>
> Hi,
>
> I have a model with a particle called 'med', which can decay into two (anti-)electron neutrinos.
>
> I now generate events of the form
>
> med > ve ve~ all all
>
> which works fine. However, afterwards I would like to use MadSpin to let the final-state particles (which might be taus etc) decay.
> When I do this, the step 'Compiling code' exists with the following error.
>
> The compilation fails with the following output message:
> gfortran -w -fPIC -ffixed-line-length-132 -c -o driver.o driver.f
> configs_decay.inc:1:12:
>
> 1 | data (map_external2res(i), i=1,6)/1,2,3 ,4 ,5 ,6 /
> | 1
> Error: Data element above array upper bound at (1)
> make: *** [<builtin>: driver.o] Error 1
>
> Before I get a warning of the form 'WARNING: Failed to update dependent parameter. This might create trouble for external program (like MadSpin/shower/...)'. However, this should not be a problem since med does not add any additional decay channels for the SM particles.
>
> For this I am using the default decaymode in madspin_card.dat. In case I set it to onshell, there are even more errors.
>
> Any ideas what might be the cause of this?
>
> Thanks for your help!
>
> Best,
> Marco
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Thanks again for the fast reply.

To clear things up:

I do not want MadSpin to handle the 'med > ve ve~ all all' decay. Instead, if the mass of med is large enough, one possible realization of this process this

med > ve ve~ w+ w-

and I want MadSpin to decay the two final-state W bosons. I can already do this with Pythia, but I wanted to include polarization and off-shell effects to get a better result. And apparently MadSpin should be able to handle this. So in total I only ask MadSpin to handle the usual SM particle decay of t, w and z.

Is this still something MadSpin cannot do?

Ah ok. Thanks for the clarification! Then I will stick to Pythia!

Best,
Marco

Thanks Olivier Mattelaer, that solved my question.