Against Dogma: On Superluminal Propagation in Classical Electromagnetism
  It is deeply entrenched dogma that relativity theory prohibits superluminal propagation. It is also experimentally well-established that under some circumstances, classical electromagnetic fields propagate through a dielectric medium with superluminal group velocities and superluminal phase velocities. But it is usually claimed that these superluminal velocities do not violate the relativistic prohibition. Here I analyze electromagnetic fields in a dielectric medium within a framework for understanding superluminal propagation recently developed by Geroch(1996, 2011) and elaborated by Earman(2014). I will argue that for some parameter values, electromagnetic fields do propagate superluminally in the Geroch-Earman sense. 
James Owen Weatherall
physics.hist-ph physics.optics