% IMPORTANT: The following is UTF-8 encoded.  This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.

@PHDTHESIS{Degner:145520,
      author       = {Degner, Andreas and DESY},
      title        = {{P}roperties of {S}tates of {L}ow {E}nergy on
                      {C}osmological {S}pacetimes},
      journal      = {DESY Thesis},
      school       = {Universität Hamburg},
      type         = {Dr.},
      reportid     = {PHPPUBDB-25927, DESY-THESIS-2013-002},
      year         = {2013},
      note         = {Universität Hamburg, Diss., 2013},
      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.},
      keywords     = {Dissertation (GND)},
      cin          = {UNI(-2012)},
      cid          = {$I:(DE-H253)UNI_-2012_-20130307$},
      pnm          = {52x - Programm Astroteilchenphysik - Topic unbekannt
                      (POF2-52x) / No facility / HGF program None (POF2-890)},
      pid          = {G:(DE-HGF)POF2-52x / G:(DE-H253)POF2-HGF-No-Prog-20130405},
      experiment   = {EXP:(DE-MLZ)NOSPEC-20140101},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)15},
      doi          = {10.3204/DESY-THESIS-2013-002},
      url          = {https://bib-pubdb1.desy.de/record/145520},
}