Exotic branes and non-geometric backgrounds

TL;DR

This paper explores exotic branes in string/M-theory, proposing they are non-geometric backgrounds called U-folds, which are crucial for understanding black hole microstates and the supertube effect.

Contribution

It introduces a higher-dimensional interpretation of exotic branes as non-geometric U-fold backgrounds, linking them to supertube effects and black hole microstate geometries.

Findings

Exotic branes are understood as non-geometric U-folds in higher dimensions.

Supergravity solutions with exotic charges relate to non-geometric backgrounds.

Implications for black hole microstate counting and non-geometric string backgrounds.

Abstract

When string/M-theory is compactified to lower dimensions, the U-duality symmetry predicts so-called exotic branes whose higher dimensional origin cannot be explained by the standard string/M-theory branes. We argue that exotic branes can be understood in higher dimensions as non-geometric backgrounds or U-folds, and that they are important for the physics of systems which originally contain no exotic charges, since the supertube effect generically produces such exotic charges. We discuss the implications of exotic backgrounds for black hole microstate (non-)geometries.