# Geodesic Structure of Naked Singularities in AdS$_3$ Spacetime

## TL;DR

This paper thoroughly analyzes the geodesic structure around naked singularities in AdS$_3$, providing explicit solutions and classifying geodesic behaviors, with implications for understanding spacetime geometry and particle trajectories.

## Contribution

It offers a complete integration and classification of geodesics in AdS$_3$ naked singularity spacetimes, including explicit solutions and analysis of their properties.

## Key findings

- Null and spacelike geodesics approach the singularity from infinity.
- Timelike geodesics are bounded and do not always fall into the singularity.
- Spatial geodesics can have self-intersections and circular orbits.

## Abstract

We present a complete study of the geodesics around naked singularities in AdS$_3$, the three-dimensional anti-de Sitter spacetime. These stationary spacetimes, characterized by two conserved charges --mass and angular momentum--, are obtained through identifications along spacelike Killing vectors with a fixed point. They are interpreted as massive spinning point particles, and can be viewed as three-dimensional analogues of cosmic strings in four spacetime dimensions. The geodesic equations are completely integrated and the solutions are expressed in terms of elementary functions. We classify different geodesics in terms of their radial bounds, which depend on the constants of motion. Null and spacelike geodesics approach the naked singularity from infinity and either fall into the singularity or wind around and go back to infinity, depending on the values of these constants, except for the extremal and massless cases for which a null geodesic could have a circular orbit. Timelike geodesics never escape to infinity and do not always fall into the singularity, namely, they can be permanently bounded between two radii. The spatial projections of the geodesics (orbits) exhibit self-intersections, whose number is particularly simple for null geodesics. As a particular application, we also compute the lengths of fixed-time spacelike geodesics of the static naked singularity using two different regularizations.