ABSTRACT

In recent years a new understanding of the dynamic role of tachyons in string theory has started to emerge. In the context of more healthy superstrings without tachyons, the phenomenon of tachyon condensation sheds some new light on the solitonic interpretation of the D-branes. This chapter presents two main examples corresponding to pairs Dp-Dp-brane-antibrane which support an open tachyon on the world-volume spectrum and the case of configurations of unstable non-BPS D-branes. In both cases tachyon condensation allows to interpret stable BPS D-branes as topologically stable extended objects, or solitons, of the auxiliary gauge theory defined on the world-volume of the original configuration of unstable D-branes. The mechanism for decay into closed-string vacua by tachyon condensation can be used to define a new algebraic structure to characterize D-brane stability and D-brane charges.