This MadGraph implementation is no longer maintained. It has been superseeded by the new FeynRules version which can be found at the FeynRules website. Click on "Model database" and then "Minimal Higgsless Model (3-Site Model)". Thank you.

MadGraph Implementation of the 3-Site Model



The 3-Site model has been implemented in Madgraph. This required a hack of the HELAS code. To run this model, you need version 4.1.31 of Madgraph and the following HELAS replacements:

Note, that once you make these HELAS changes, this version of Madgraph will no longer work for any other model! You must make two separate madgraph directories. One with these changes where you run the 3-site model. Another without these modifications where you run every other model (eg. the sm).

Warning: These Helas routines are not always run by MadEvent in the way I intended. This generates incorrect cross sections for some processes. This is fixed in the new FeynRules version of this model for MadGraph. Please see the link at the top of this page.

Model Files

Once you have madgraph set up, you need the model files:

I have included a set of param_card.dat files for various W' masses and very large heavy fermion masses (intended for being removed from the calculation). An example is param_card-w500NF.dat, where the 500 refers to the W' mass in GeV. These should be copied to param_card.dat when they are desired.


If another set of parameters is desired, a few things should be remembered:

  • MW , MZ and sinW must be related by MW = MZ cosW.
  • Once a W' mass is chosen, the user should run the program "couplings" in the model directory. At the top of the output, there will be a line that tells the user what to set the Z' mass as.
  • Once a Dirac mass is chosen, again the user should save param_card.dat and run "couplings" in the model directory. At the top of the output, there will be a line that tells the user what to set the heavy top quark mass as, and another that tells the user what to set all the other heavy fermion masses as.
  • Once a new set of masses is chosen, the user will need to run BRIDGE to set the widths and branching ratios correctly. BRIDGE will fail on the widths of the heavy fermions when they become very large. Also, at least version 1.06 of BRIDGE should be used.


The model is set up so that the user can decide whether to turn the heavy fermions on or off. An example of a proc_card.dat file can be found below:

QCD-HF and QED-HF are the QCD and QED vertices that contain one or more heavy fermions. If these are set to zero, then no heavy fermions will be included in the calculation. However, note that if this is done, the heavy fermion masses should still be taken large, since they can still affect the couplings constants of the light fermions if they are not.

Topic attachments
I Attachment Action SizeSorted ascending Date Who Comment
proc_card.datdat proc_card.dat manage 3 K 12 Feb 2008 - 18:25 UnknownUser Example proc_card.dat
wwwwxx.FF wwwwxx.F manage 5 K 12 Feb 2008 - 18:23 UnknownUser HELAS routine
jwwwxx.FF jwwwxx.F manage 6 K 12 Feb 2008 - 18:23 UnknownUser HELAS routine
w3w3xx.FF w3w3xx.F manage 6 K 12 Feb 2008 - 18:24 UnknownUser HELAS routine
jw3wxx.FF jw3wxx.F manage 8 K 12 Feb 2008 - 18:24 UnknownUser HELAS routine
3-site.tgztgz 3-site.tgz manage 474 K 12 Feb 2008 - 18:25 UnknownUser 3-Site Model files
This topic: ThreeSiteModel > WebHome > MadGraph
Topic revision: 10 Aug 2009, NeilChristensen
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