In chapter 3 the relation between two different classes of perturbative non-BPS bi-spinor states of heterotic string theory and certain non-perturbative non-BPS D-brane states of the dual type I' theory is exhibited. The domains of stability of these states as well as their decay products in both theories are determined and shown to agree with the duality map. In chapter 4 the effects of the non-BPS D-instanton in type I theory and its M-theory origin is described. The starting point is the tree-level amplitude for the scattering of two gauge particles in the HorĖava-Witten formulation of M-theory. At low momenta this exactly reproduces the corresponding tree-level scattering amplitude of the <I>E</I><SUB>8</SUB> x <I>E</I><SUB>8</SUB> heterotic string theory. After compactification to nine dimensions this amplitude is used to describe the scattering of two massive <I>SO</I>(16) spinor states. The non-BPS D-instanton component of this amplitude is explicitly determined from this expression. In chapter 5 the renormalization group method is used to study tachyon condensation on bosonic D25-brane. The decay of the D25-brane is controlled by a nearby IR fixed point representing D24-branes. The boundary entropy corresponding to the D24-brane tension is calculated in leading order in perturbation theory and agrees with the expected result to an accuracy of 8%. Multicritical behaviour of the IR theory suggests that the end point of the flow represents a configuration of two D24-branes. An analogy with Kondo physics is discussed. Chapter 6 ongoing developments in the context of little string theory and matrix theory.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:598293 |
| Date | January 2001 |
| Creators | Dasgupta, T. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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