The KK-Monopole/NS5-Brane in Doubled Geometry

TL;DR

This paper constructs the T-dual of the KK-monopole/NS5-brane system within doubled geometry, demonstrating the formalism's effectiveness in capturing non-geometric features and instanton effects despite broken isometries.

Contribution

It explicitly constructs the T-dual system in doubled geometry and extends the formalism to gauged linear sigma models, enhancing understanding of non-geometric backgrounds.

Findings

Successfully describes the T-dual system in doubled geometry

Shows the formalism handles broken isometries

Provides a doubled perspective on worldsheet instanton effects

Abstract

The Kaluza-Klein monopole has been recognized as a string background with significant non-geometric features: it must appear "localized" to winding strings to match the NS5-brane's localization on the T-dual circle. In this work, we explicitly construct this T-dual system in the doubled geometry formalism, which proves to successfully describe the duality despite a broken isometry on one side of the duality pair. We further suggest an extension of the doubled formalism to the gauged linear sigma models describing this system (both bosonic and supersymmetric) and show that previous calculations of worldsheet instanton effects are best understood in this doubled form.