Isolated horizons of the Hopf bundle structure transversal to the null direction, the horizon equations and embeddability in NUT-like spacetimes

TL;DR

This paper explores isolated horizons with Hopf bundle structures in NUT-like spacetimes, characterizing their geometry, solutions, and relation to known Kerr-NUT-(Anti) de Sitter spacetimes, including conditions for regular extremal horizons.

Contribution

It introduces a new analysis of horizons with Hopf bundle structures not tangent to null directions and constructs corresponding spacetimes with specific parameters.

Findings

Derived all horizons satisfying the vacuum type D equation.

Compared horizons to those in accelerated Kerr-NUT-(Anti) de Sitter spacetimes.

Constructed spacetimes with specified parameters and analyzed singularities.

Abstract

Isolated horizons that admit the Hopf bundle structure $H\rightarrow S_2$ are investigated, however the null direction is allowed not to be tangent to the bundle fibres. The geometry of such horizons is characterised by data set on a topological two-dimensional sphere, singular at its poles. The horizon equations induced by Einstein's equations are imposed. The existence of regular extremal horizons satisfying the vacuum (with cosmological constant) equation of extremality, obtained from singular solutions on the sphere is pointed out. All horizons (with assumed topology and in the generic case) satisfying the $\Lambda$ vacuum type D equation are derived. They are compared to the Killing horizons contained in the accelerated Kerr-NUT-(Anti) de Sitter spacetimes. Both families of horizons have the same dimension, but the problem of mutual correspondence needs to be better understood. If the cosmological constant takes special values determined by the other parameters the bundle fibers become tangent to the null direction. As an additional but also important result, spacetimes of the topology $H\times \mathbb{R}$ locally isometric to the accelerated Kerr-NUT-(Anti) de Sitter spacetimes are constructed for every value of the mass, Kerr, NUT parameters, the cosmological constant and the acceleration. When the acceleration parameter is not zero, the conical singularity can be removed whenever the NUT parameter does not vanish either.