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@PHDTHESIS{Heeba:826075,
      author       = {Heeba, Saniya},
      othercontributors = {Kahlhöfer, Felix Karl David and Krämer, Michael},
      title        = {{D}oors to darkness: {P}henomenology of dark matter portal
                      interactions},
      school       = {RWTH Aachen University},
      type         = {Dissertation},
      address      = {Aachen},
      publisher    = {RWTH Aachen University},
      reportid     = {RWTH-2021-08734},
      pages        = {1 Online-Ressource : Illustrationen},
      year         = {2021},
      note         = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
                      University; Dissertation, RWTH Aachen University, 2021},
      abstract     = {The Dark Matter (DM) question has taken centre-stage in
                      modern-day particle physics and cosmology, with the
                      microphysical nature of DM remaining stubbornly elusive. In
                      this thesis, we explore different classes of particle DM
                      models based on the interactions of DM with the Standard
                      Model (SM). Our interests lie in obtaining accurate relic
                      density estimates with the inclusion of finite temperature
                      corrections and other in-medium effects, as well as in
                      detailing the detection prospects of these models using
                      direct detection experiments and accelerator searches. We
                      will focus on the so-called portal models, in which a single
                      type of interaction connects the DM particle to the SM. We
                      will distinguish between the case where this portal
                      interaction arises from the exchange of a scalar,
                      $\textit{the Higgs Portal}$, and from a vector particle,
                      $\textit{the vector portal}$. For the Higgs portal, we
                      consider a scalar singlet DM model where the relic abundance
                      is set by the leakage of energy from the SM thermal bath
                      (the so-called $\textit{freeze-in mechanism}$), and where
                      the dominant contribution does not arise from Higgs boson
                      decays. The latter can be achieved if such decays are
                      kinematically forbidden or if the reheating temperature is
                      much smaller than the Higgs boson mass. For the vector
                      portal, we consider two dark photon models. One, with a
                      kinetically mixed dark photon where the relic abundance is
                      set by resonantly enhanced annihilations during or after
                      $\textit{freeze-out}$, i.e., when DM decouples from the
                      thermal bath. And the second, where both the SM and DM are
                      gauged under an additional $U(1)^\prime$, and the relic
                      abundance is set by freeze-in. Further, mediators in both
                      scalar and vector portal models may also give rise to
                      long-range DM-DM interactions, potentially alleviating the
                      tensions between astrophysical observations and predictions
                      from collisionless cold DM. To discuss these effects, we
                      provide a new quantum-mechanical treatment of such
                      self-interactions and derive analytic results for the
                      momentum transfer and viscosity cross-section for the case
                      of interactions arising from a Yukawa potential. Through
                      these representative models, we make the following
                      observations: i) Thermal corrections, in-medium effects and
                      a proper treatment of the electroweak and QCD phase
                      transition are highly relevant for relic density
                      calculations especially for the case of freeze-in, and ii)
                      some of the simplest models with light and/or feebly coupled
                      DM can be probed in a complementary fashion at ongoing and
                      upcoming direct detection and accelerator experiments,
                      spelling exciting times for the future of DM research.},
      cin          = {139610 / 130000},
      ddc          = {530},
      cid          = {$I:(DE-82)139610_20160614$ / $I:(DE-82)130000_20140620$},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.18154/RWTH-2021-08734},
      url          = {https://publications.rwth-aachen.de/record/826075},
}