  A detailed analysis of vacuum Cherenkov radiation in spacelike
Maxwell-Chern-Simons (MCS) theory is presented. A semiclassical treatment
reproduces the leading terms of the tree-level result from quantum field
theory. Moreover, certain quantum corrections turn out to be suppressed for
large energies of the charged particle, for example, the quantum corrections to
the classical MCS Cherenkov angle. It is argued that MCS-theory Cherenkov
radiation may, in principle, lead to anisotropy effects for ultra-high-energy
cosmic rays (UHECRs). In addition, a qualitative discussion of vacuum Cherenkov
radiation from a modified-Maxwell term in the action is given, together with
UHECR bounds on some of its dimensionless "coupling constants."
