When quantizing boson fields, ghosts and gauge-fixing terms seem to break gauge invariance. The unitary gauge (where there are no ghosts or gauge-fixing terms) respects gauge invariance however. So which is correct - is the Standard Model a gauge theory or not? Sometimes I hear people speak about breaking Lorentz invariance. Does anyone have any idea what they mean? I think it has to do with CPT symmetry. There is a close relationship between CPT symmetry and Lorentz symmetry - one practically implies the other. So if CPT is broken, then I think that's where they are saying Lorentz symmetry is broken. Does this sound like pseudo-science, because Lorentz symmetry seems to be sacred?