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Jul22-08, 02:45 PM
P: 18
OK. Let's think of a massive electron. As long as it cannot propagate with the speed of light, it cannot have definite helicity, as we can boost to the other frame, where our electron's helicity would change. But again, as long as our electron is massive, it will have both parts, the left-handed and right-handed, of the Dirac spinor. So, how can we decide if our electron is of right-handed chirality or that of left-handed?