On the role of closed timelike curves and confinement structure around Kerr-Newman singularity

TL;DR

This paper explores particle dynamics around Kerr-Newman singularities, revealing how causality violations and confinement structures influence particle motion and the nature of closed timelike curves in these spacetimes.

Contribution

It provides a detailed analysis of particle trajectories and confinement regions near Kerr-Newman singularities, highlighting the effects of charge, angular momentum, and spacetime structure on closed timelike curves.

Findings

Singularities are hidden behind causality-violating regions in Kerr-Newman spacetimes.

Particles with positive angular momentum can traverse closed timelike curves under certain conditions.

An empty region around the singularity prevents particles from interacting directly with it.

Abstract

In this study, the particle motion around the naked singularity and black hole of Kerr-Newman spacetime is investigated with a special attention on the closed timelike orbits. It is found that both in the naked singularity (NS) and in black hole (BH), the singularity is concealed by causality violating regions, and the Cauchy surface consistently resides inside the inner horizon in non-extremal black holes. For neutral particles and particles with an identical charge to the source, only particles with positive angular momentum are permitted to traverse the closed timelike curves. Conversely, for particles with the opposite charge to the source, the strong Coulomb attraction draws all particles inside the Cauchy surface, allowing them to be present in the closed timelike curves irrespective of their angular momentum. However, in both the NS and BH (both extremal and non-extremal), test particles are confined at a considerable distance from the singular point such that there always exists an empty region surrounding the singularity which prevents particles from interacting with it. The radius of the empty surface that depends on the source parameters and the particle characteristics, is investigated with an accurate expression.