D branes in string theory,I

TL;DR

The work surveys the origin and construction of boundary states as a string-theoretic description of D$p$-branes, bridging open string boundary conditions and closed string exchange through open/closed channel duality. It demonstrates how T-duality necessitates Dirichlet boundaries, identifies D$p$-branes with classical RR-charged p-brane solutions, and derives BRST-invariant boundary states in both bosonic and supersymmetric settings. By projecting boundary states onto massless closed-string modes, the long-distance fields of D$p$-branes reproduce the corresponding supergravity solutions in ten dimensions, and brane interactions computed in open and closed channels coincide, yielding no-force for BPS configurations via the abstruse identity. Together, these results weave a coherent link between perturbative string theory, boundary states, and non-perturbative brane dynamics in Type II theories.

Abstract

In these lectures we present a detailed description of the origin and of the construction of the boundary state that is now widely used for studying the properties of D branes. (Lectures given at NATO-ASI on "Quantum Geometry" in Akureyri, Iceland, August 1999).