Consequences of a condensed matter realization of Lorentz violating QED   in Weyl semi-metals
  In Lorentz violating quantum electrodynamics (QED) it is known that a radiatively induced Chern-Simons term appears in the effective action for the gauge field, which is finite but undetermined. This ambiguity is shown to be absent in a condensed matter realization of such a theory in Weyl semi-metals due to the existence of a full microscopic model from which this effective theory emerges. Physically observable consequences such as birefringence are also discussed in this scenario. 
Adolfo G. Grushin
hep-th cond-mat.mtrl-sci