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## Main Question or Discussion Point

Hi, I am currently studying quantum field theory with worldwidely used text written by Peskin and Schroeder. On page 165 of that text it says, " the amplitude vanishes unless the final photon is right-handed." But I cannot figure out how it works. With ε = (0,1,i,0), I get same expression located right after 5.100, which result in 0 when it applies to [itex] u_R = \pmatrix{ 0 \cr 1} [/itex]. I think there must be something related to photon polarization and I am missing. Could you find where I got wrong? Thanks in advance.