Abstract: | In this work, we present the results of searches for signatures of dark
matter decay or annihilation into Standard Model particles, and secret neutrino
interactions with dark matter. Neutrinos could be produced in the decay or
annihilation of galactic or extragalactic dark matter. Additionally, if an
interaction between dark matter and neutrinos exists then dark matter will
interact with extragalactic neutrinos. In particular galactic dark matter will
induce an anisotropy in the neutrino sky if this interaction is present. We use
seven and a half years of the High-Energy Starting Event (HESE) sample data,
which measures neutrinos in the energy range of approximately 60 TeV to 10 PeV,
to study these phenomena. This all-sky event selection is dominated by
extragalactic neutrinos. For dark matter of $sim$ 1 PeV in mass, we constrain
the velocity-averaged annihilation cross section to be smaller than
$10^{-23}$cm$^3$/s for the exclusive $mu^+mu^-$ channel and $10^{-22}$
cm$^3$/s for the $bar b$ channel. For the same mass, we constrain the
lifetime of dark matter to be larger than $10^{28}$ s for all channels studied,
except for decaying exclusively to $bar b$ where it is bounded to be larger
than $10^{27}$ s. Finally, we also search for evidence of astrophysical
neutrinos scattering on galactic dark matter in two scenarios. For fermionic
dark matter with a vector mediator, we constrain the dimensionless coupling
associated with this interaction to be less than 0.1 for dark matter mass of
0.1 GeV and a mediator mass of $10^{-4}~$ GeV. In the case of scalar dark
matter with a fermionic mediator, we constrain the coupling to be less than 0.1
for dark matter and mediator masses below 1 MeV. |