Dear Florian,

I have a model with a Dirac field \Chi which is coupled to a pseudo-scalar
\phi as
L = g \phi \Chi \gamma^5 \chi
(g is a Yukawa coupling).
I have trouble with defining the Lagrangian in the model file.
(I would like to define a Dirac fermion and then defining the interaction
Lagrangian which has a Gamma^5 in it).

Would appreciate it if you help us with this problem

Best regards,

Hi,

it's not possible to define the Potential terms using Dirac fermions. You need to use Weyl notation. To see how your concrete cases works, take a look at the model SM+VL/CPoddS where a CP-odd singlet is coupled to vectorlike fermions.

Cheers,
Florian