  Vacuum Cerenkov radiation is possible in certain Lorentz-violating quantum
field theories, when very energetic charges move faster than the phase speed of
light. In the presence of a CPT-even, Lorentz-violating modification of the
photon sector, the character of the Cerenkov process is controlled by the
high-frequency behavior of the radiation spectrum. The development of the
Cerenkov process can be markedly different, depending on whether the only
limits on the emission of very energetic photons come from energy-momentum
conservation or whether there are additional effects that cut off the spectrum
at high frequencies. Moreover, since the high-frequency cutoff determines the
total rate at which an emitting charge loses energy, it also controls all
aspects of the emission that are related to the process's finite duration.
