TASI Lectures on Non-BPS D-Brane Systems

TL;DR

This paper reviews properties of D-branes, focusing on unstable and non-BPS D-branes, their classification via K-theory, and discusses specific cases in type I and type I' theories, highlighting their stability, spectrum, and unresolved issues.

Contribution

It provides a comprehensive overview of non-BPS D-branes, including their construction, classification, and spectrum in various compactifications, with emphasis on type I and type I' theories.

Findings

Construction of stable non-BPS D0-branes in type I theory.

Classification of D-brane charges using K-theory.

Identification of problems with D7 and D8-branes in type I theory.

Abstract

In this set of lectures various properties of D-branes are discussed. After reviewing the basics, we discuss unstable D-brane/anti-D-brane systems, a subject pioneered by Sen. Following him, we discuss the construction of the non-BPS D0-brane in type I theory. This state is stable since it carries a conserved Z_2 charge. The general classification of D-brane charges using K-theory is discussed. The results for the type I theory, and the T-dual type I' theory, are emphasized. Compactification of type I on a circle or torus gives a theory with 16 supersymmetries in 9d or 8d. In each case the moduli space has three branches. The spectrum of non-BPS D-branes are different for each of these branches. We conclude by pointing out some problems with the type I D7-brane and D8-brane predicted by K-theory.