Chronology protection and the stringy exclusion principle

TL;DR

This paper constructs supersymmetric solutions in AdS supergravity with closed timelike curves and proposes a mechanism involving light degrees of freedom to remove these curves, linking it to the stringy exclusion principle in the dual CFT.

Contribution

It introduces a new mechanism using tensionless branes to excise closed timelike curves, connecting supergravity solutions with unitarity bounds in the dual CFT.

Findings

Closed timelike curves can be removed via an enhancon-like mechanism.

The removal of CTCs corresponds to the stringy exclusion principle.

Supersymmetric solutions exhibit a link between geometry and CFT unitarity bounds.

Abstract

We construct a family of supersymmetric solutions to AdS supergravity in three dimensions, that correspond to type IIB seven branes wrapped on an internal S3xT4. These solutions are generalizations of the three dimensional Goedel universe and have closed timelike curves. We propose an enhancon-like mechanism for excising the closed timelike curve region by including the effects of additional light degrees of freedom. These take the form of tensionless 7-brane probes, effectively described through the backreaction of a smeared domain wall. The absence of closed timelike curves in the asymptotic AdS3 geometries obtained in this way is shown to be equivalent to a unitarity bound in the dual CFT, known as the stringy exclusion principle.