In our lecture it was said that the reason why in QED, interaction terms of the form:
$\bar \psi \psi A_\mu^2$ do not appear is because this term has a mass dimension 5 and it would require a coupling of mass dimension $-1$ so that the lagrange density is 4. And if that is the case, the theory is not renormalizable.
But why is non-renormalizable ? And what does it mean for a theory to be as such?
