K-theoretic matching of brane charges in S- and U-duality

TL;DR

This paper explores how K-theory can be used to match D-brane charges in a complex string duality scenario involving type I and type IIA theories, resolving previous issues with torsion charges.

Contribution

It demonstrates that replacing K3 with its orbifold blow-down enables precise K-theoretic matching of brane charges in a less understood duality case.

Findings

Successful matching of 2-torsion brane charges.

Resolution of theoretical problems using orbifold blow-down.

Extension of K-theoretic methods to complex dualities.

Abstract

We discuss K-theoretic matching of D-brane charges in the string duality between type I on the 4-torus and type IIA on a K3 surface. This case is more complex than the familiar case of IIA/IIB duality, which is already well understood, but it turns out that replacing K3 by its orbifold blow-down seems largely to resolve the apparent problems with the theory. In particular, this allows for precise matching of 2-torsion brane charges.