Thanks for your answer, it make sense. Do you think you need to explicitly use the WT identities for showing that the divergent parts of the amplitudes cancel each other, at a given order of perturbation theory? Or that cancellation is it just a consequence of the presence of gauge invariance?
I have a question about Fadeev-Popov (FP) ghosts.
FP ghosts brake the gauge symmetry of the lagrangian and solve the problem of the divergence of the physical amplitudes, due to the gauge equivalence of the states. My question is: is it a renormalization process? I mean, the renormalization...
What I don't understand about WT identity is how it allows or helps you to renormalize a quantum field theory (es. QED). Not in details, just the basic ideas, if possible.
Thanks in advice