Cherenkov radiation in isotropic chiral matter: unlocking threshold-free emission
We investigate Cherenkov radiation in isotropic chiral matter using Carroll-Field-Jackiw electrodynamics, with an axion angle linear in time, to describe a charge moving at constant velocity. By solving the modified Maxwell's equations in cylindrical coordinates and in the space-frequency domain, we derive closed expressions for the circularly polarized electromagnetic fields contributing independently to the radiation. The dispersion relations are obtained by imposing causality at a cylindrical surface at infinity, ensuring outgoing waves. Contrary to initial suppositions, each spectral energy distribution is gauge-invariant and positive, describing radiation at a characteristic angle. We characterize the angles and identify frequency ranges that allow for zero, one, or two Cherenkov cones. Notably, one sector of the model enables threshold-free Cherenkov radiation from slowly moving charges. Our results agree with partial findings in the nonrelativistic limit of earlier iterative analysis and clarify the regimes in which Cherenkov radiation arises in isotropic chiral matter.