Dirichlet-Branes and Ramond-Ramond Charges

TL;DR

This paper demonstrates that Dirichlet-branes in string theory carry Ramond-Ramond charges, break half the supersymmetry, and are essential sources consistent with string duality, revealing a new 9-form potential in type IIa string theory.

Contribution

It establishes Dirichlet-branes as fundamental Ramond-Ramond charge carriers and identifies a previously overlooked 9-form potential in type IIa string theory.

Findings

Dirichlet-branes break half of the supersymmetries.

They carry electric and magnetic Ramond-Ramond charges.

The charge quantization matches string duality predictions.

Abstract

We show that Dirichlet-branes, extended objects defined by mixed Dirichlet-Neumann boundary conditions in string theory, break half of the supersymmetries of the type~II superstring and carry a complete set of electric and magnetic Ramond-Ramond charges. We also find that the product of the electric and magnetic charges is a single Dirac unit, and that the quantum of charge takes the value required by string duality. This is strong evidence that the Dirchlet-branes are intrinsic to type II string theory and are the Ramond-Ramond sources required by string duality. We also note the existence of a previously overlooked 9-form potential in the IIa string, which gives rise to an effective cosmological constant of undetermined magnitude.