- #1

- 560

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[tex]\sum_{a} (\epsilon_{\vec{k} a } )_i ( \epsilon^*_{ \vec{k} a} )_j = \delta_{ij} -\frac{k_i k_j}{\vec{k}^2}[/tex]

Does anyone know how to derive this relation?

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- Thread starter center o bass
- Start date

- #1

- 560

- 2

[tex]\sum_{a} (\epsilon_{\vec{k} a } )_i ( \epsilon^*_{ \vec{k} a} )_j = \delta_{ij} -\frac{k_i k_j}{\vec{k}^2}[/tex]

Does anyone know how to derive this relation?

- #2

- 13,077

- 645

Check out page 36 of Cohen-Tannoudji's <Introduction to Quantum Electrodynamics>.

- #3

- 560

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Thanks! :)

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