Propagation of Fronts and Information in Dispersive Media

Abstract

We present a general proof based on Kramers-Kronig relations that, in a normal or anomalous dispersive linear medium, any (discontinuitynonanalytic disturbance) in an electromagnetic pulse can not propagate faster than the phase velocity, $c$. Consequently the information carried by the discontinuity (nonanalytical disturbance) can not be transmitted superluminally.

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