Cherenkov radiation as ghost instability

Abstract

We demonstrate that Cherenkov radiation can be interpreted as ghost instability of a certain type. Solutions of modified gravity theories often contain ghost instabilities. One type of such ghost instability is associated with existence of different types of species with causal cones that do not share common time, which leads to vacuum decay via creation of particles with positive and negative energies. We show that this ghost instability can be seen as Cherenkov radiation and vice versa.