Issues with dipole operator from FeynRules

Asked by Joel Jones

Dear MadGraph team,

I have taken an existing FeynRules model (heavyN) and added dim-5 effective operators. Everything works fine until I add dipole operators:

convert model /home/jjones/Programs/MG5_aMC_v2_9_2/models/heavyNeff5_all_UFO
import model heavyNeff5_all_UFO --modelname
compute_widths n4 --body_decay=3

Please note that the automatic computation of the width is only valid in narrow-width approximation and at tree-level.
INFO: load particles
INFO: load vertices
INFO: Get two body decay from FeynRules formula
Command "compute_widths n4 --body_decay=3 " interrupted in sub-command:
"compute_widths n4 --body_decay=3" with error:
SyntaxError : invalid syntax (<string>, line 1)
Please report this bug on
More information is found in 'MG5_debug'.
Please attach this file to your report.

The MG5_debug is not very helpful. It includes:
Traceback (most recent call last):
  File "/home/jjones/Programs/MG5_aMC_v2_9_2/madgraph/interface/", line 1541, in onecmd
    return self.onecmd_orig(line, **opt)
  File "/home/jjones/Programs/MG5_aMC_v2_9_2/madgraph/interface/", line 1490, in onecmd_orig
    return func(arg, **opt)
  File "/home/jjones/Programs/MG5_aMC_v2_9_2/madgraph/interface/", line 346, in do_compute_widths
    return self.cmd.do_compute_widths(self, *args, **opts)
  File "/home/jjones/Programs/MG5_aMC_v2_9_2/madgraph/interface/", line 8520, in do_compute_widths
    value = eval(expr,{'cmath':cmath},data).real
  File "<string>", line 1

Then comes a long line of code involving the coefficient of the dipole operator, I copy a short part of it:
 ((mdl_mN4**2 - mdl_MZ**2)*((mdl_ee**2*mdl_mN4**2*mdl_VeN4**2)/(2.*mdl_cw**2*mdl_sw**2) + (mdl_ee**2*mdl_mN4**4*mdl_VeN4**2)/(2.*mdl_cw**2*mdl_MZ**2*mdl_sw**2) - (mdl_ee**2*mdl_MZ**2*mdl_VeN4**2)/(mdl_cw**2*mdl_sw**2) + (2*mdl_alphaNB4e*mdl_ee*complex(0,1)*mdl_mN4*mdl_VeN4*complexconjugate(Sig(Index(Lorentz,mu$11095),Index(Lorentz,PRIVATExeext(2))))*FV(2,Index(Lorentz,mu$11095))*FV(2,Index(Lorentz,PRIVATExeext(2))))/mdl_cw - (2*mdl_alphaNB4e*mdl_ee*complex(0,1)*mdl_mN4**3*mdl_VeN4*complexconjugate(Sig(Index(Lorentz,mu$11095),Index(Lorentz,PRIVATExeext(2))))*FV(2,Index(Lorentz,mu$11095))*FV(2,Index(Lorentz,PRIVATExeext(2))))/(mdl_cw*mdl_MZ**2)

It then finishes with:
SyntaxError: invalid syntax
Related File: <string>

And I am stumped. I have adapted the dipole operator from the file of the BSM Characterisation model in the FeynRules page, so I really do not know what I am doing wrong.

This might be a long shot, but could it be a MadGraph issue related to the Majorana nature of the neutrinos?

Many thanks for your attention.

Question information

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Solved by:
Olivier Mattelaer
Last query:
Last reply:
Revision history for this message
Best Olivier Mattelaer (olivier-mattelaer) said :


This is a FeynRules issue. Your file (part of the UFO) is clearly not correctly formatted (the expression you quote is not a valid python syntax as it should be).

So I'm not really able to help you on that. What you can do is to remove the full file (since it is optional). This will slow down the computation of the width but it should go trough. The second solution is of course to ask FeynRules author for support.



Revision history for this message
Joel Jones (n-jones-j) said :

Thanks Olivier Mattelaer, that solved my question.

Revision history for this message
Joel Jones (n-jones-j) said :

Thanks for the info!