Rotating Black Holes, Closed Time-Like Curves, Thermodynamics, and the Enhancon Mechanism

TL;DR

This paper extends the enhançon mechanism to rotating five-dimensional BPS black holes realized as D1–D5 branes on K3×S^1, showing that enhançon loci prevent potential Second Law violations and inhibit CTC formation via brane charge additions. Through the 10D/5D/2D descriptions, it derives the rotating enhançon radii for bound-state probes, confirms consistency via probe action cancellations and excision geometries, and demonstrates that shell formation at the enhançon radii preserves horizon entropy. The results reinforce a sharp link between microscopic brane dynamics and macroscopic thermodynamic laws, while concluding that the enhançon mechanism does not universally eliminate CTCs but forbids their manufacture through physical processes in this class of geometries. Overall, the work highlights how stringy mechanisms can enforce fundamental principles like the Second Law by preventing problematic brane configurations from reaching horizons.

Abstract

We reconsider supersymmetric five dimensional rotating charged black holes, and their description in terms of D-branes. By wrapping some of the branes on K3, we are able to explore the role of the enhancon mechanism in this system. We verify that enhancon loci protect the black hole from violations of the Second Law of Thermodynamics which would have been achieved by the addition of certain D-brane charges. The same charges can potentially result in the formation of closed time-like curves by adding them to holes initially free of them, and so the enhancon mechanism forbids this as well. Although this latter observation is encouraging, it is noted that this mechanism alone does not eliminate closed time-like curves from these systems, but is in accord with earlier suggestions that they may not be manufactured, in this context, by physical processes.