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I need to evaluate the following dot products

[tex]\vec{\epsilon}_{k,\,s}\cdot\vec{\epsilon}_{-k,\,s'} = ?[/tex]

[tex]\vec{\epsilon}_{k,\,s}^*\cdot\vec{\epsilon}_{-k,\,s'}^* = ?[/tex]

[tex]\vec{\epsilon}_{k,\,s}^*\cdot\vec{\epsilon}_{-k,\,s'}^* = ?[/tex]

where [itex]\vec\epsilon_{k,\,s}[/itex] is the normalized polarization vector for a single photon with momentum [itex]k[/itex], and spin [itex]s[/itex]. Does anyone know where I can look for these identities?