CPT and Lorentz violation en the Photon and $Z$-boson sector

Symmetry 2017, 9(11), 248 CPT and Lorentz violation in the photon sector is described within the minimal Standard-Model Extension by a dimension-3 Chern-Simons-like operator parametrized by a four-vector parameter $k_{AF}$ that has been very tightly bounded by astrophysical observations. On the other hand, in the context of the $SU(2)\times U(1)$ electroweak gauge sector of the Standard-Model Extension, CPT and Lorentz violation is described similarly, by dimension-3 operators parametrized by four-vector parameters $k_1$ and $k_2$. In this work, we investigate in detail the effects of the resulting CPT and Lorentz violation in the photon and $Z$-boson sectors upon electroweak-symmetry breaking. In particular, we show that for the photon sector the relevant Lorentz-violating effects are described at lowest order by the $k_{AF}$ term, but that there are higher-order momentum-dependent effects due to photon-$Z$ boson mixing. As bounds on CPT and Lorentz violation in the $Z$ sector are relatively weak, these effects could be important phenomenologically. We investigate these effects in detail in this work.