I recently learned that with (local) gauge invariance, functional quantization needs to factor out volume factor(Faddeev-Popov procedure).(adsbygoogle = window.adsbygoogle || []).push({});

Why does this has to be done?Just to remove infinity? As far as I am concerned, ##\phi^4## theory contains invariance(for example ##\phi\to\phi\cdot e^{i \alpha}##) but do not need such procedure.

What is the difference between the invariance in ##\phi^4## theory and that of Yang-mills theory? I learned that guage invariance is redundant freedom but what's the exact meaning of redundant freedom?

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# Gauge invariance is not normal invariance?

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