# Open exceptional strings and D-branes

## TL;DR

This paper develops a framework for defining D-branes within exceptional field theory by formulating boundary conditions compatible with supersymmetry, enabling the study of D-branes in complex U-fold backgrounds.

## Contribution

It introduces a method to define D-branes in exceptional geometry using open string boundary conditions and projectors, extending previous work to include S-duals and U-fold backgrounds.

## Key findings

- Defined open string boundary conditions in exceptional geometry
- Constructed Neumann and Dirichlet projectors preserving supersymmetry
- Provided a new perspective on D-branes in U-fold backgrounds

## Abstract

We study D-branes in the extended geometry appearing in exceptional field theory (or exceptional generalised geometry). Starting from the exceptional sigma model (an $E_{d(d)}$ covariant worldsheet action with extra target space coordinates), we define open string boundary conditions. We write down Neumann and Dirichlet projectors compatible with the preservation of half-maximal supersymmetry by the brane (building on previous work on the definition of generalised orientifold quotients in exceptional field theory). This leads to a definition of D-branes, plus their S-duals, as particular subspaces of the exceptional geometry, and provides an opportunity to study D-branes in U-fold backgrounds.