Help with this Standard Model demonstration please

[Andreaca]

I want to demonstrate that calculating the squared amplitude of the process quark antiquark in lepton antilepton where I consider the non-zero masses of the fermions, is equivalent to considering the zero masses but with infinite insertions of the vev. I am trying to do it, but the pieces I find that diverge do not have opposite signs. Could you help me?

 

[Mordred]

Might help if you show what you have so far. Also if you square the negative frequency amplitude what result do you get (positive or negative) ?
Then ask yourself the question on a probability amplitude such as provided by the Schrödinger equations
" is a negative probability valid ? "