Universal Horizons without Hypersurface Orthogonality
arXiv:2504.07215 · doi:10.1103/2l2x-y6yr
Abstract
A key consequence of Lorentz-violating gravity is the emergence of modified dispersion relations implying the absence of a universal maximum propagation speed. This challenges the conventional notion of the event horizon as a causal boundary common to all degrees of freedom. However, certain solutions in these theories exhibit \emph{universal horizons} -- surfaces capable of trapping signals of arbitrarily high speed, thereby restoring the notion of black hole. Previous studies have extensively characterised universal horizons in settings where Lorentz violation is encoded via a hypersurface-orthogonal æther. In this work, we explore the possibility of extending this concept to more general cases where hypersurface orthogonality is relaxed. To do so, we construct a candidate trapping surface and analyse its causal properties using a general model for Lorentz-violating matter. We find that, in addition to the standard conditions associated to universal horizons, a local vanishing of the æther's twist is also necessary. We then provide an explicit example of such a universal horizon by suitably deforming the æther flow in a stealth Kerr solution recently found in Einstein--æther theory. Moreover, we analyse the behaviour of trajectories which are not analytical at the universal horizon and discuss the implications of our findings for Hawking radiation. While our analysis is motivated by Einstein-æ{t}her gravity, our results apply to broader classes of Lorentz-violating theories, further supporting the relevance of black hole phenomenology in these frameworks.
28+ pages, no figures. (v2) Two clarifying comments added below eq.s (2.1) and (2.3) after review, no substantial changes; matches published version
References in corpus (26)
- Quantum Gravity at a Lifshitz Point
- Models of non-relativistic quantum gravity: the good, the bad and the healthy
- On the Extra Mode and Inconsistency of Horava Gravity
- Planck-scale modified dispersion relations and Finsler geometry
- Black holes in Einstein-aether and Horava-Lifshitz gravity
- Spontaneous breaking of Lorentz invariance, black holes and perpetuum mobile of the 2nd kind
- Lorentz violation and perpetual motion
- Investigation on Finsler geometry as a generalization to curved spacetime of Planck-scale-deformed relativity in the de Sitter case
- Built-in scordatura in U-DHOST
- Universal horizons and black holes in gravitational theories with broken Lorentz symmetry
- Effective Field Theory of Black Hole Perturbations with Timelike Scalar Profile: Formulation
- Quasinormal Modes from EFT of Black Hole Perturbations with Timelike Scalar Profile
- Universal horizons in maximally symmetric spaces
- Cancellation of divergences in the nonprojectable Horava theory
- The relation between general relativity and a class of Hořava gravity theories
- On the effective metric of axial black hole perturbations in DHOST gravity
- On the first law of black holes with a universal horizon
- Hawking Radiation in Lorentz Violating Gravity: A Tale of Two Horizons
- Time Orientability and Particle Production from Universal Horizons
- Black holes, multiple propagation speeds, and energy extraction
- Kerr Black Hole in Einstein--Æther Gravity
- Gravitational Tunneling in Lorentz Violating Gravity
- BRST symmetry and unitarity of the Horava theory
- Renormalization of the nonprojectable Horava theory
- Minimal Einstein-Aether Theory
- Black hole horizons at the extremal limit in Lorentz-violating gravity