Prof Andre Lukas

Abstract:

We study flop transitions for M-theory on Calabi-Yau threefolds and their applications to cosmology in the context of the effective five-dimensional supergravity theory. In particular, the additional hypermultiplet which becomes massless at the transition is included in the effective action. We find the potential for this hypermultiplet which includes quadratic and quartic terms as well as additional dependence on the Kähler moduli. By constructing explicit cosmological solutions, it is demonstrated that a flop transition can indeed be achieved dynamically, as long as the hypermultiplet is set to zero. For an explicit example we find that once excitations of the hypermultiplet are taken into account, the transition is genetically not completed but the system is classically stabilized close to the transition region, at least as long as the transition states do not vanish. Regions of moduli space close to flop transitions can, therefore, be viewed as preferred by the cosmological evolution. ©2003 The American Physical Society.

Abstract:

We present a toy model for five-dimensional heterotic M theory where bulk three-branes, originating in 11 dimensions from M five-branes, are modeled as kink solutions of a bulk scalar field theory. It is shown that the vacua of this defect model correspond to a class of topologically distinct M-theory compactifications. Topology change can then be analyzed by studying the time evolution of the defect model. In the context of a four-dimensional effective theory, we study in detail the simplest such process, that is, the time evolution of a kink and its collision with a boundary. We find that the kink is generically absorbed by the boundary thereby changing the boundary charge. This opens up the possibility of exploring the relation between more complicated defect configurations and the topology of brane-world models. © 2003 The American Physical Society.