Worldsheet Description of Tachyon Condensation in Open String Theory

Tadaoki Uesugi

Published 2003-02-17, updated 2003-02-26Version 2

In this thesis we review the fundamental framework of boundary string field theory (BSFT) and apply it to the tachyon condensation on non-BPS systems in the superstring theory. The boundary string field theory can be regarded as a natural extension of the nonlinear sigma model. By using this theory we can describe the tachyon condensation exactly and also obtain the effective actions on non-BPS systems consisting of the Dirac-Born-Infeld type action and the Wess-Zumino type action. Especially the Wess-Zumino action is written by superconnection and coincides with the mathematical argument by K-theory. Moreover we also discuss the tachyon condensation keeping the conformal invariance (on-shell). The exact argument by using the boundary state formalism gives a good support to the conjecture of the tachyon condensation and it is also consistent with boundary string field theory.