I have dug several resources from the internet, but none happen to explain the following formula:(adsbygoogle = window.adsbygoogle || []).push({});

##1 = \int \frac{dp}{(2\pi)^{3}} |\vec{p}><\vec{p}|##

I have done basic quantum mechanics, so I know that this is the completeness relation. Also, I understand that an integral is being taken over all the momentum states. That's all fine by me.

What's tripping me up is the factor of ##(2\pi)^{3}##.

Can someone explain where they come from. I've thinking it has to do with Fourier analysis or something because the same funny factor appears when Fourier transform into momentum space.

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# Completeness relation

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