•The amplitude

We can safely set the photon mass to zero:

ParticleMass[Photon, ___] := 0 ;

Calculation of the amplitude:

ampFC = Plus @@ CreateFCAmp[inserttops] // Contract

(e^(0 ))^2 ϕ ( -p _ 3 , m _ ψ^(ó  0 ) ) . γ^μ _ 1 . ϕ ( p _ 2 , m _ ψ^(ó  0 ) ) ϕ ( -p _ 4 , m _ ψ^(ó  0 ) ) . γ^μ _ 1 . ϕ ( p _ 1 , m _ ψ^(ó  0 ) ) 1/(-p _ 2 - p _ 3)^2 - (e^(0 ))^2 ϕ ( -p _ 3 , m _ ψ^(ó  0 ) ) . γ^μ _ 2 . ϕ ( p _ 1 , m _ ψ^(ó  0 ) ) ϕ ( -p _ 4 , m _ ψ^(ó  0 ) ) . γ^μ _ 2 . ϕ ( p _ 2 , m _ ψ^(ó  0 ) ) 1/(-p _ 2 - p _ 4)^2

Converted by Mathematica  (July 10, 2003)