DBI Analysis of Open String Bound States on Non-compact D-branes

Chapter 5Branes“Many speak <strong>of</strong> the legendary and gigantic starship Titanic,a majestic and luxurious cruise liner [which] hadthe misfortune to be built in the very earliest days <strong>of</strong> ImprobabilityPhysics, long before this difficult and cussedbranch <strong>of</strong> knowledge was fully, or at all, understood. Thedesigners and engineers decided, in their innocence, tobuild a prototype Improbability Field into it, which wasmeant, supposedly, to ensure that it was Infinitely Improbablethat anything would ever go wrong with anypart <strong>of</strong> the ship. They did not realize that because <strong>of</strong> thequasi-reciprocal and circular nature <strong>of</strong> all Improbabilitycalculations, anything that was Infinitely Improbable wasactually very likely to happen almost immediatly.”Douglas AdamsHitchhiker’s Guide to the GalaxyDespite its name, string theory does not exclusively handle about strings. Other physicalobjects also inhabit this theory, amongst which we find the D-branes and NS5-branes,both being special cases <strong>of</strong> general p-branes: objects that extend in p dimensions <strong>of</strong>space. This chapter aims to introduce these two protagonists, concentrating on theType II superstring theory case, since that is the one that concerns us in the carried outresearch.5.1 Dp-branesA Dp-brane is a physical object that lives in D-dimensional space-time, and extendsin p spatial dimensions (with p < D), and hence describes a (p + 1)-dimensional worldvolume. One does not always specify the p, in which case one simply talks about D-branes. The defining property <strong>of</strong> a D-brane is that open strings with Dirichlet boundary60