Comment 2 for bug 861263

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:
Exception : WRONG CONTRACTION OF LORENTZ OBJECT for routine FFVSS4_2
Please report this bug on https://bugs.launchpad.net/madgraph5
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.