The source of $CPT$ violation in the photon sector of the Standard Model Extension arises from a Chern-Simons-like contribution that involves a coupling to a fixed background vector field $k_{AF}^{\mu }$. These Lorentz- and $CPT$-violating photons have well-known theoretical issues that arise from missing states at low momenta when $k_{AF}^{\mu }$ is timelike. In order to make the theory consistent, a tiny mass for the photon can be introduced, well below current experimental bounds. The implementation of canonical quantization can then be implemented as in the $CPT$-preserving case by using the Stückelberg mechanism. We explicitly construct a covariant basis of properly normalized polarization vectors at fixed three-momentum satisfying the momentum space field equations, in terms of which the vector field can be expanded. As an application of the theory, we calculate the Cherenkov radiation rate for the case of purely timelike $k_{AF}^{\mu }$ and find a radiation rate at high energies that has a contribution that does not depend on the mass used to regulate the photons.

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• Photons
• Lorentz symmetry
• Chern-Simons gauge theory