Supertube domain-walls and elimination of closed time-like curves in string theory

TL;DR

This work presents a general mechanism by which domain-walls constructed from smeared supertubes excise closed time-like curves from Gödel-type and rotating spacetimes. By analyzing the moduli space of supertubes near the velocity-of-light surface, the authors show that the tube delocalizes into a domain-wall, leaving an interior Gödel-like region and an exterior rotating geometry, thereby preventing CTCs behind horizons. The construction is demonstrated across multiple backgrounds (one- and two-angular-momentum cases, and extrapolated to three-charge black holes) and is supported by Israel junction-condition consistency checks, suggesting a broad causality-protection principle in string theory. The results connect to known mechanisms like the enhançon and have potential implications for black-hole microstate geometries and non-perturbative dual descriptions, with future work aimed at extending to additional backgrounds and less symmetric configurations.

Abstract

We show that some novel physics of supertubes removes closed time-like curves from many supersymmetric spaces which naively suffer from this problem. The main claim is that supertubes naturally form domain-walls, so while analytical continuation of the metric would lead to closed time-like curves, across the domain-wall the metric is non-differentiable, and the closed time-like curves are eliminated. In the examples we study the metric inside the domain-wall is always of the Gödel type, while outside the shell it looks like a localized rotating object, often a rotating black hole. Thus this mechanism prevents the appearance of closed time-like curves behind the horizons of certain rotating black holes.