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| Dissertation / PhD Thesis/Internal Report | PHPPUBDB-25927 |
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2013
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Please use a persistent id in citations: doi:10.3204/DESY-THESIS-2013-002
Report No.: DESY-THESIS-2013-002
Abstract: The present thesis investigates properties of a class of physical states of the quantised scalar field in FRW spacetimes, namely the states of low energy (SLE’s). These states are characterised by minimising the time-smeared energy density measured by an isotropic observer, where the smearing is performed with respect to a test function f of compact support. Furthermore, they share all spatial symmetries of the spacetime. Since SLE’s are Hadamard states, expectations values of observables like the energy density can be rigorously defined via the so called point-splitting method. In a first step, this procedure will be applied to the explicit calculation of the energy density in SLE’s for the case of de Sitter space with flat spatial sections. In particular, the effect of the choice of the mass m and the test function f will be discussed. The obtained results motivate the question whether SLE’s converge to a distinguished state (namely the Bunch Davies state) when the support of f is shifted to the infinite past. It will be shown that this is indeed the case, even in the more general class of asymptotic de Sitter spacetimes, where an analogon of the Bunch Davies state can be defined. This result enables the interpretation of such distinguished states to be SLE’s in the infinite past, independently of the form of the smearing function f . Finally, the role of SLE’s for the semiclassical backreaction problem will be discussed. We will derive the semiclassical Friedmann equation in a perturbative approach over Minkowski space. This equation allows for a stability analysis of Minkowski space by the investigation of asymptotic properties of solutions. We will also treat this problem using a numerical method.
Keyword(s): Dissertation
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