Equilibrium conditions of spinning test particles in Kerr-de Sitter spacetimes

TL;DR

This paper investigates the equilibrium conditions and spin dynamics of spinning test particles in Kerr-de Sitter spacetimes, revealing spin-dependent effects and specific equilibrium locations influenced by cosmic repulsion and rotation.

Contribution

It provides the first detailed analysis of equilibrium conditions for spinning particles in Kerr-de Sitter spacetimes, highlighting spin effects and equilibrium positions in these complex geometries.

Findings

Equilibrium conditions depend on particle spin and location.

Equilibrium at the static radius involves arbitrary spin orientations.

On the symmetry axis, equilibrium occurs at any radius with specific spin tuning.

Abstract

Equilibrium conditions and spin dynamics of spinning test particles are discussed in the stationary and axially symmetric Kerr-de Sitter black-hole or naked-singularity spacetimes. The general equilibrium conditions are established, but due to their great complexity, the detailed discussion of the equilibrium conditions and spin dynamics is presented only in the simple and most relevant cases of equilibrium positions in the equatorial plane and on the symmetry axis of the spacetimes. It is shown that due to the combined effect of the rotation of the source and the cosmic repulsion the equilibrium is spin dependent in contrast to the spherically symmetric spacetimes. In the equatorial plane, it is possible at the so-called static radius, where the gravitational attraction is balanced by the cosmic repulsion, for the spinless particles as well as for spinning particles with arbitrarily large azimuthal-oriented spin or at any radius outside the ergosphere with a specifically given spin orthogonal to the equatorial plane. On the symmetry axis, the equilibrium is possible at any radius in the stationary region and is given by an appropriately tuned spin directed along the axis. At the static radii on the axis the spin of particles in equilibrium must vanish.