Lorentz andCPTviolating Chern-Simons term in the derivative expansion of QED

We calculate, by the method of dimensional regularization and derivative expansion, the one-loop effective action for a Dirac fermion with a Lorentz-violating and CPT-odd kinetic term in the background of a gauge field. We show that this term induces a Chern-Simons modification to Maxwell theory. Some related issues are also discussed.