Stability and thermodynamics of black rings

TL;DR

This paper analyzes the stability and thermodynamic properties of five-dimensional rotating black rings, revealing instability in one branch, stability changes at branch intersections, and phase transition-like behavior at extremality.

Contribution

It applies the Poincare stability method and thermodynamic geometry to black rings, providing new insights into their stability and phase structure.

Findings

One black ring branch is always unstable.

Stability changes occur at branch intersection points.

Extremality exhibits behavior similar to second order phase transitions.

Abstract

We study the phase diagram of D=5 rotating black holes and the black rings discovered by Emparan and Reall. We address the issue of microcanonical stability of these spacetimes and its relation to thermodynamics by using the so-called ``Poincare method'' of stability. We are able to show that one of the BR branches is always unstable, with a change of stability at the point where both BR branches meet. We study the geometry of the thermodynamic state space (``Ruppeiner geometry'') and compute the critical exponents to check the corresponding scaling laws. We find that, at extremality, the system exhibits a behaviour which, formally, is very similar to that of a second order phase transition.