Hello! I am a bit confused about the completeness relation for photon polarization. So it says ## \sum_{s=1,2}\epsilon_i^s\epsilon_j^{s*}=\delta_{ij}-p_ip_j##, with ##p_i, p_j## - unit vectors. So I am not sure what are the indices i and j. I though that they represent the component of the vector, but in that case the RHS would be always 0. So what are i and j? Thank you!(adsbygoogle = window.adsbygoogle || []).push({});

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# I Photon Polarization

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