Negative Refractive Index in Hydrodynamical Systems
  We discuss the presence of exotic electromagnetic phenomena in systems with finite charge density which are described by hydrodynamics. We show that such systems generically have negative refractive index for low frequency electromagnetic waves, i.e. the energy flux and the phase velocity of the wave propagate in opposite directions. We comment on possible phenomenological applications, focusing on the Quark Gluon Plasma. 
Antonio Amariti, Davide Forcella and Alberto Mariotti
hep-th hep-ph physics.optics physics.plasm-ph