addition of four particle vertex does not give cross-section value comparable to the theory
Hello,
I want to simulate a model of spin 0 magnetic monopoles where the diagrams are :
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The process has one 4 particles vertex (photon-
To achieve that, I have written a MadGraph UFO model which is kept here:
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The coupling of the 4 particle vertex is defined here:
https:/
The Lorentz structure is defined here:
https:/
There is no compilation issue and MadGraph is giving me a total cross-section based on this model. But unfortunately, when I compare the cross-section value with the theoretical prediction, I see that the two values differ significantly.
Interestingly, when I multiply the Lorentz factor of the 4 particle vertex by 10:
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the cross-section values of MadGraph and the theory matches. The cross-section plot is shown here:
https:/
This was a scalar-
When I use spin 1/2 magnetic monopole (with a similar UFO model, but monopole spin is now 1/2), the process does not have any 4 particle vertex. The diagrams are here:
https:/
. There the theory and MadGraph cross-section match fantastically:
https:/
Does this mean the 4 particle vertex calculation is unstable for MadGraph5? Is there any way MadGraph model can reproduce the theoretical prediction when there is a 4 particle vertex?
Any help is appreciated.
Thank you,
Arka
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