A substrate for brane shells from $T\bar{T}$

TL;DR

This paper explores a new way to resolve singularities in certain string theory geometries related to $T\bar{T}$ deformations by using a shell of branes, providing a UV-completion that avoids problematic features.

Contribution

It proposes an alternative UV-completion for $T\bar{T}$-deformed geometries by cutting and gluing to a regular background, involving brane shells and the enhançon mechanism.

Findings

A regular background approach resolves singularities in $T\bar{T}$-deformed geometries.

Brane shells and the enhançon mechanism provide a physical interpretation of negative branes.

The new solutions offer a consistent UV-completion avoiding closed timelike curves.

Abstract

A solvable current-current deformation of the worldsheet theory of strings on $AdS_3$ has been recently conjectured to be dual to an irrelevant deformation of the spacetime orbifold CFT, commonly referred to as single-trace $T\bar{T}$. These deformations give rise to a family of bulk geometries which realize a non-trivial flow towards the UV. For a particular sign of this deformation, the corresponding three-dimensional geometry approaches $AdS_3$ in the interior, but has a curvature singularity at finite radius, beyond which there are closed timelike curves. It has been suggested that this singularity is due to the presence of "negative branes," which are exotic objects that generically change the metric signature. We propose an alternative UV-completion for these geometries by cutting and gluing to a regular background which approaches a linear dilaton vacuum in the UV. In the S-dual picture, a singularity resolution mechanism known as the enhan\c{c}on induces this transition by the formation of a shell of $D5$-branes at a fixed radial position near the singularity. The solutions involving negative branes gain a new interpretation in this context.