2,465 research outputs found
New Production Mechanism for keV Sterile Neutrino Dark Matter by Decays of Frozen-In Scalars
We propose a new production mechanism for keV sterile neutrino Dark Matter.
In our setting, we assume the existence of a scalar singlet particle which
never entered thermal equilibrium in the early Universe, since it only couples
to the Standard Model fields by a really small Higgs portal interaction. For
suitable values of this coupling, the scalar can undergo the so-called
freeze-in process, and in this way be efficiently produced in the early
Universe. These scalars can then decay into keV sterile neutrinos and produce
the correct Dark Matter abundance. While similar settings in which the scalar
does enter thermal equilibrium and then freezes out have been studied
previously, the mechanism proposed here is new and represents a versatile
extension of the known case. We perform a detailed numerical calculation of the
DM production using a set of coupled Boltzmann equations, and we illustrate the
successful regions in the parameter space. Our production mechanism notably can
even work in models where active-sterile mixing is completely absent
A consistent model for leptogenesis, dark matter and the IceCube signal
We discuss a left-right symmetric extension of the Standard Model in which
the three additional right-handed neutrinos play a central role in explaining
the baryon asymmetry of the Universe, the dark matter abundance and the ultra
energetic signal detected by the IceCube experiment. The energy spectrum and
neutrino flux measured by IceCube are ascribed to the decays of the lightest
right-handed neutrino , thus fixing its mass and lifetime, while the
production of in the primordial thermal bath occurs via a freeze-in
mechanism driven by the additional interactions. The constraints
imposed by IceCube and the dark matter abundance allow nonetheless the heavier
right-handed neutrinos to realize a standard type-I seesaw leptogenesis, with
the asymmetry dominantly produced by the next-to-lightest neutrino .
Further consequences and predictions of the model are that: the
production implies a specific power-law relation between the reheating
temperature of the Universe and the vacuum expectation value of the
triplet; leptogenesis imposes a lower bound on the reheating temperature of the
Universe at 7\times10^9\,\mbox{GeV}. Additionally, the model requires a
vanishing absolute neutrino mass scale .Comment: 19 pages, 4 figures. Constraints from cosmic-ray antiprotons and
gamma rays added, with hadrophobic assignment of the matter multiplets to
satisfy bounds. References added. Matches version published in JHE
Enhancing Dark Matter Annihilation into Neutrinos
We perform a detailed and quasi model-independent analysis of direct
annihilation of Dark Matter into neutrinos. Considering different cases for
scalar and fermionic Dark Matter, we identify several settings in which this
annihilation is enhanced, contrary to some statements in the literature. They
key point is that several restrictions of, e.g., a supersymmetric framework do
not hold in general. The mass generation mechanism of the neutrinos plays an
important role, too. We illustrate our considerations by two examples that are
not (as usually) suppressed by the smallness of the neutrino mass, for which we
also present a numerical analysis. Our results can be easily used as guidelines
for model building.Comment: 33 pages, 2 figure
Leptophilic Dark Matter in Direct Detection Experiments and in the Sun
Dark matter interacting predominantly with leptons instead of nuclear matter
has received a lot of interest recently. In this talk, we investigate the
signals expected from such 'leptophilic Dark Matter' in direct detection
experiments and in experiments looking for Dark Matter annihilation into
neutrinos in the Sun. In a model-independent framework, we calculate the
expected interaction rates for different scattering processes, including
elastic and inelastic scattering off atomic electron shells, as well as
loop-induced scattering off atomic nuclei. In those cases where the last effect
dominates, leptophilic Dark Matter cannot be distinguished from conventional
WIMPs. On the other hand, if inelastic scattering off the electron shell
dominates, the expected event spectrum in direct detection experiments is
different and would provide a distinct signal. However, we find that the
signals in DAMA and/or CoGeNT cannot be explained by invoking leptophilic DM
because the predicted and observed energy spectra do not match, and because of
neutrino bounds from the Sun.Comment: 7 pages, 3 figures, prepared for the Proceedings of the 8th
International Workshop on Identification of Dark Matter (IDM 2010), July
26-30, 2010, University of Montpellier II, Montpellier, Franc
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