Problem wih vertex FFSS and Pythia --fixed

Bug #861263 reported by Jeremy Neveu
This bug affects 1 person
Affects Status Importance Assigned to Milestone
Olivier Mattelaer

Bug Description


I'm trying to plug a new model involving a scalar field with Feynrules/Madgraph5/Pythia8. Everything is ok until I want to make an output for pythia8 :

ALOHA: aloha creates VVV1 routines
ALOHA: aloha creates SSSS1 routines
ALOHA: aloha creates FFSS1 routines
Command "output pythia8 test -f" interrupted with error:
  File "/home/irfulx174/mnt/jneveu/Documents/CMS/MonteCarlo/MadGraph5_v1_3_16/madgraph/iolibs/", line 1894, in write_aloha_routines
  File "/home/irfulx174/mnt/jneveu/Documents/CMS/MonteCarlo/MadGraph5_v1_3_16/aloha/", line 469, in compute_all
    self[(, outgoing)].add_combine(m)
KeyError: ('FFSS1', 4)

If I run only output test -f, there is no problem, so I guess it comes from the interfacing between MadGraph and Pythia, or maybe a limitation of Pythia (but I don't find information about that). Can you help me please?


Revision history for this message
Jeremy Neveu (jneveu) wrote :

Thanks Johan for your quick answer! Here are the UFO files. I was trying p p > a pi pi process.


Changed in madgraph5:
assignee: nobody → Olivier Mattelaer (olivier-mattelaer)
Revision history for this message
Olivier Mattelaer (olivier-mattelaer) wrote :

Hi Jeremy,

Thanks a lot for this bug report. This is in fact an ALOHA bug and not a MG5 bug (that's the reason why Johan send the bug to me).

The bug that you point is quite easy to fix. (I will push this in the next version)

 But your model is also subject to another bug:
ALOHA: aloha creates FFSSS1 routines
ALOHA: aloha creates FFSSS2 routines
ALOHA: aloha creates FFVSS1 routines
ALOHA: aloha creates FFVSS2 routines
ALOHA: aloha creates FFVSS3 routines
ALOHA: aloha creates FFVSS4 routines
ALOHA: aloha creates VVVSS1 routines
ALOHA: aloha creates VVVVSS1 routines
ALOHA: aloha creates VVVVSS2 routines
ALOHA: aloha creates VVVVSS3 routines
Command "output pythia8" interrupted in sub-command:
"import model BUG_FIX; generate p p > a pi pi;output pythia8" with error:
Please report this bug on
More information is found in 'MG5_debug'.
Please attach this file to your report.

So this is related to the routine:

FFVSS4 = Lorentz(name = 'FFVSS4',
                 spins = [ 2, 2, 3, 1, 1 ],
                 structure = '-8*P(-1,4)*P(-1,5)*Gamma(-2,2,1) + 2*P(-2,5)*P(-1,4)*Gamma(-1,2,1) + 2*P(-2,4)*P(-1,5)*Gamma(-1,2,1)')

And indeed you can see that the indices -2 is not contracted to anything else, and the index 3 (corresponding to the vector)
is not present.

Did you create this from FR (If I read your post, it seems so)?
If so you will need to make a report to the FR group.

Note that you have similar problem with FFVSS2. Off course in your case, you can probably fix those two routines by hand.

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) wrote :

I've push the new version in the trunk.

Thanks a lot,


Changed in madgraph5:
status: New → Fix Released
importance: Undecided → Medium
milestone: none → 1.3.0
summary: - Problem wih vertex FFSS and Pythia
+ Problem wih vertex FFSS and Pythia --fixed
Revision history for this message
Jeremy Neveu (jneveu) wrote :

Yes I created the model with Feynrules, I will report the bug.

Thanks a lot for your help!


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