ABSTRACT

This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book reviews the supergravity effective actions of type II string theories, the classical field equations that follow from these actions and the simplest brane solutions. It also reviews the boundary state formalism to describe Dirichlet branes, and discusses the case in which an external field is present on their world-volume. The book shows how supergravity classical D-brane solutions can be recovered from the boundary state. It emphasizes that the twofold interpretation of the D-branes, as classical supergravity solutions and as spacetime defects where open strings can terminate, is a direct consequence of a duality between open and closed strings which allows a double interpretation of the annulus/cylinder diagram. The boundary state has been extensively used to describe the properties and interactions of the D-branes, both in flat and in curved backgrounds.