Universal horizons and black holes in gravitational theories with broken Lorentz symmetry

TL;DR

This paper extends the concept of universal horizons to Lorentz-violating theories, finds various black hole solutions with universal horizons in Horava-Lifshitz gravity, and discusses their properties and existence in the full theory.

Contribution

It generalizes the definition of universal horizons to broader theories with broken Lorentz symmetry and explores their presence in static charged solutions within Horava-Lifshitz gravity.

Findings

Universal horizons exist inside Killing horizons in studied solutions.

Surface gravity at universal horizons varies relative to Killing horizons.

Black holes with universal horizons are present in the full HL gravity theory.

Abstract

In this paper, we first show that the definition of the universal horizons studied recently in the khrononmetric theory of gravity can be straightforwardly generalized to other theories that violate the Lorentz symmetry, by simply considering the khronon as a probe field and playing the same role as a Killing vector field. As an application, we study static charged ($D+1$)-dimensional spacetimes in the framework of the healthy (non-projectable) Horava-Lifshitz (HL) gravity in the infrared limit, and find various solutions. Some of them represent Lifshitz space-times with hyperscaling violations, and some have black hole structures. In the latter universal horizons always exist inside the Killing horizons. The surface gravity on them can be either larger or smaller than the surface gravity on the Killing horizons, depending on the space-times considered. Although such black holes are found only in the infrared, we argue that black holes with universal horizons also exist in the full theory of the HL gravity. A simple example is the Schwarzschild solution written in the Painleve-Gullstrand coordinates, which is also a solution of the full theory of the HL gravity and has a universal horizon located inside the Schwarzschild Killing horizon.