Spacetime symmetries of the Lorentz-violating Maxwell-Chern-Simons model

The spacetime symmetries of classical electrodynamics with a Chern-Simons term containing a constant nondynamical 4-vector are investigated. In addition to translation invariance and the three remaining Lorentz symmetries characterized by the little group of the external vector, the model possesses an additional spacetime symmetry if this vector is lightlike. The associated conserved current is determined, and the resulting symmetry algebra is identified as sim(2).