# Implementing 4-fermion operators in LanHEP

Dear CalcHEP experts,

I am trying to implement 4-fermion vertices involving singlet Majorana/Dirac BSM field with SM fermion fields in LanHEP to use the model files further in CalcHEP and in MicrOmegas. Now, I am experiencing a couple of things for which I need some help to understand them:

(a) For implementing an operator with, say, vector current e.g., c_q*\bar{

(b) In the expression for \sigma.v I am always getting a factor of 2 less from the model file when I'm comparing the results with analytical expressions. I am unable to find out the error. Does the LanHEP use some different normalization to relate the operator scale with the mass of the auxiliary field? maybe I am missing something here.

(c) For interactions which are not Hermitian conjugate, omitting the 'AddHermConj' command in LanHEP is not showing any error. Again, is that due to a wrong auxiliary field implementation?

I can send my model files if you wish to see them. Thank you for the help.

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- Solved by:
- Alexander Belyaev

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