The Enhancon and the Consistency of Excision

TL;DR

This paper investigates the enhancon mechanism in supergravity, demonstrating that the excision of singularities via brane shells is consistent at the gravitational level and can be extended to non-extremal cases with horizons.

Contribution

It shows the gravitational consistency of the enhancon excision process and explores non-extremal generalizations allowing for horizons within the interior geometry.

Findings

The source at the excision surface behaves like a shell of wrapped D6-branes.

Tension vanishes at the enhancon radius, confirming the shell's physical nature.

The procedure can be extended to non-extremal geometries with horizons.

Abstract

The enhancon mechanism removes a family of time-like singularities from certain supergravity spacetimes by forming a shell of branes on which the exterior geometry terminates. The problematic interior geometry is replaced by a new spacetime, which in the prototype extremal case is simply flat. We show that this excision process, made inevitable by stringy phenomena such as enhanced gauge symmetry and the vanishing of certain D-branes' tension at the shell, is also consistent at the purely gravitational level. The source introduced at the excision surface between the interior and exterior geometries behaves exactly as a shell of wrapped D6-branes, and in particular, the tension vanishes at precisely the enhancon radius. These observations can be generalised, and we present the case for non-extremal generalisations of the geometry, showing that the procedure allows for the possibility that the interior geometry contains an horizon. Further knowledge of the dynamics of the enhancon shell itself is needed to determine the precise position of the horizon, and to uncover a complete physical interpretation of the solutions.