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Vacuum ε = 1 contour deformations ω(ξ) and their corresponding (real frequency) physical realizations εc(ξ)
|
ξ → ω(ξ) |
ε → εc(ξ) |
Physical realization |
 |
εc(ξ) | Any physical material |
| iξ | −1 | Violate K-K as ξ → 0 |
| ξeiϕ | e2iϕ | |
 |
1 + iσ/ξ | Conductor |
