>>16552613
>but it’s blatantly wrong upon closer inspection
There is absolutely nothing wrong with it you retard. Using the polar decomposition in the form he's mentioned is common and more sensible when you're proving topological properties of groups because you want to exclude non-invertible matrices. Stop doubling down on your retardation.
>But there is no covering group involved in either ISO(2) or SO(2).
I looked at his reasoning and nowhere does it involve anything about the representation restricted to the little group. He derives the fact about spins using the fact that the representation is defined on all of SL(2, C). If you just restrict yourself to representations of the little group like you're doing, then the massless particle would have different allowed values of helicities for each direction and there would be no relation between these helicities at all, a manifestly nonsensical result arising because you're making bizarre non-physical assumptions.

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>be a math guy>decide to dabble in QFT>get told picrel is the most rigorous introduction to the subject>literally zero…

>be a math guy
>decide to dabble in QFT
>get told picrel is the most rigorous introduction to the subject
>literally zero…