- #1
Silviu
- 624
- 11
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!