Gravity seminar - Ian Vega Seminar

The possibility of Lorentz-symmetry violations in gravity has been a matter of interest for some time. Notable recent progress has been made towards constraining Lorentz violations in the strong-field regime with astrophysical observations. At a more basic level, Lorentz violations force the black hole event horizon to relinquish its role as an absolute causal boundary. In its place is a surrogate structure, the so-called universal horizon, which all known black hole solutions in Lorentz-violating theories (e.g. Horava and Einstein-aether) seem to possess. However, all of these known black hole solutions are spherically symmetric, which raises the question of whether or not the universal horizon is generic or merely a symmetry artefact. In this talk, I shall discuss new rotating solutions in three-dimensional Horava gravity and slowly-rotating solutions in Einstein-aether theory. These solutions suggest that universal horizons may not be robust enough to rescue the concept of a black hole in Lorentz-violating theories of gravity.