Time-dependent backgrounds of string theory
Alexander Maloney · CERN Document Server (European Organization for Nuclear Research) · 2003
This thesis is devoted to the study of time-dependent backgrounds in string theory. The first chapter contains a brief, non-technical introduction to the subject. In the second chapter quantum field theory in d-dimensional de Sitter space is studied, with an emphasis on the dS/CFT correspondence. We study a one-parameter family of dS-invariant vacua; this bulk vacuum dependence is dual to a deformation of the boundary CFT by a marginal operator. In odd spacetime dimensions the state with no particles on I- has no particles on I+ , implying the absence of particle production. In Kerr-dS, a thermal density matrix is found by tracing over causally inaccessible modes. Assuming Cardy's formula, the microscopic entropy of such a thermal state in the boundary CFT precisely equals the Bekenstein-Hawking value. Next, we construct de Sitter vacua of supercritical string theories in D > 10 dimensions. Compactifying D − 4 of these dimensions on a carefully constructed asymmetric orientifold projects out the continuous moduli of the compact directions. By adding specific fluxes we generate dilaton potentials with nontrivial minima at arbitrarily small cosmological constant and string coupling. We then discuss the decay of such metastable de Sitter vacua. For sufficiently large potential barriers the standard gravitational instantons violate both causality and low- energy decoupling, raising the possibility that these de Sitter vacua are stable. In the final chapter we study spacelike branes as exact, boundary deformed worldsheet CFTs. Open string pair production is thermal, as can be seen from either a Bogolyubov transformation or an Unruh detector argument. Moreover, there exist exactly thermal mixed states which define a Euclidean effective field theory on the S-brane world-volume. By computing the boundary state of this theory we determine the long range closed string production. At a critical value of the coupling the S- brane reduces to an array of sD-branes on the imaginary time axis. In real time this corresponds to a purely closed string configuration with no D-branes, yet the long range force felt by an observer is proportional that produced by the original unstable D-brane.