Critical velocity and event horizon in pair-correlated systems with "relativistic" fermionic quasiparticles

The condition for the appearance of event horizon is considered in such pair-correlated systems (superfluids and superconductors) where the fermionic quasiparticles obey the "relativistic" equations. In these systems, the Landau critical velocity of superflow corresponds to the speed of light. In conventional systems, such as s-wave superconductors, the superflow remains stable even above the Landau treshold. We showed that in the "relativistic" systems however the quantum vacuum becomes unstable and the superflow collapses after the "speed of light" is reached, so that horizon cannot appear. Thus an equilibrium dissipationless superfluid flow state and the horizon are incompatible due to quantum effects. This negative result is consistent with the quantum Hawking radiation from the horizon, which would lead to the dissipation of the flow.