Ray tracing Einstein-{\AE}ther black holes: Universal versus Killing horizons

摘要

Violating Lorentz-invariance, and so implicitly permitting some form ofsuperluminal communication, necessarily alters the notion of a black hole.Nevertheless, in both Einstein-{\AE}ther gravity, and Ho\v{r}ava-Lifshitzgravity, there is still a causally disconnected region in black-hole solutions;now being bounded by a "Universal horizon", which traps excitations ofarbitrarily high velocities. To better understand the nature of these blackholes, and their Universal horizons, we study ray trajectories in thesespacetimes. We find evidence that Hawking radiation is associated with theUniversal horizon, while the "lingering" of ray trajectories near the Killinghorizon hints at reprocessing there. In doing this we solve an apparentdiscrepancy between the surface gravity of the Universal horizon and theassociated temperature derived by tunneling method. These results advance theunderstanding of these exotic horizons, and provide hints for a fullunderstanding of black-hole thermodynamics in Lorentz-violating theories.