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Nov26-10, 09:46 PM
P: 136
For massive particles, the chirality depends on the reference frame; so boosting can take one between left and right chiralities. For massless particles, the handedness cannot change with boosting to different frames. Otherwise, the handedness of chirality for massive particles has the same meaning as the handedness of the helicity for massless particles. An electron with spin component +1/2 relative to the z-axis can look like it has spin component -1/2 if you go to a frame that's moving in the z-direction relative to the electron. (The presence of the mass term in the Dirac equation "spoils" the reducibility of the equation into left and right pieces, which would otherwise be called Weyl equations).