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There has been 2 questions that bother me and couldn't find a good answer to them. Maybe some experts out there could help?

Question 1:

It is said that the representation of photon spin-up is

-(1/Sqrt(2)) (1, i, 0)

And the representation of photon spin-down is

(1/Sqrt(2)) (1, -i, 0)

Why? And where did these come from?

The place where I saw the above being used is in Griffiths's text Elementary Particles PG 244 EQ 7.156. That's where he uses these to compute the amplitude with rules derived from Feynmann calculus.

Question 2:

Photon is known to be a spin 1 particle, but why does it have just two states? Shouldn't there be 3? I consulted a book and it says that it has to do with the fact that photon has zero mass. What does mass have to do with this?

Thank you for your response! I appreciate it!

Joe

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# A question that bothers me - Photon spin up/down state?

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