Say, I want to couple the angular momenta of a electron spin angular momentum, and a photon's momentum. I guess in terms of representations it's:(adsbygoogle = window.adsbygoogle || []).push({});

[itex]SU(2) \otimes [U(1) \oplus U(1)] = [SU(2) \otimes U(1)] \oplus [SU(2) \otimes U(1)][/itex]

But I'm not at all certain if this is correct, one thing for example, U(1) represents liittle group SO(2), but SU(2) represents SO(3), I probably shouldn't just put them together by a direct product, etc.

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# How to couple the angular momenta of a massive particle and a massless one

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