In this thesis, we discuss time-dependent solutions of the low-energy limit of heterotic M-theory. In particular, we are interested in cases where the solution undergoes a dynamical transition from a five- to a four-dimensional description. We give explicit examples of such cases, and show how to match the properties of the different regimes. We begin by discussing how the five- and four-dimensional actions arise in heterotic M-theory, and why reduction differs from that of a standard Kaluza-Klein compacti- fication. The truncated actions relevant for our cosmological solutions are presented, and the process of compactification on a non-trivial vacuum is explained in detail. We derive various cosmological solutions, both of the heterotic M-theory action and a more phenomenologically motivated action relevant for inflation, and discuss the conditions necessary for these solutions to possess a four-dimensional limit. We pay particular attention to the behaviour of these solutions in the four-dimensional regime. VVe give a brief introduction to inflation, explaining why this epoch could potentially provide observable signatures of Horava- Witten cosmology. Having derived solutions with an (A)dS5 bulk and dS4 branes, we consider the slow-roll conditions that must be imposed if these backgrounds are to be upgraded to inflationary models. We show that the structure of the five-dimensional space places strong restrictions on a bulk scalar field. An example of a five-dimensional inflationary background which becomes four-dimensional as slow-roll progresses is found. Finally, we consider the problem of stabilization of the four-dimensional moduli during inflation. Specifically, in the context of the weakly coupled heterotic string we are interested in whether the dilaton can naturally be stabilized near its present value at the time of inflation. We demonstrate a fairly generic mechanism that ensures the gauge coupling at the unification scale was at the approximately the same value during inflation as today. The consequences of this for inflationary model-building are discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:558719 |
| Date | January 2003 |
| Creators | Skinner, David |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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