4,143 research outputs found
Galactic Center Excess in Gamma Rays from Annihilation of Self-Interacting Dark Matter
Observations by the Fermi-LAT telescope have uncovered a significant
-ray excess toward the Milky Way Galactic Center. There has been no
detection of a similar signal in the direction of the Milky Way dwarf
spheroidal galaxies. Additionally, astronomical observations indicate that
dwarf galaxies and other faint galaxies are less dense than predicted by the
simplest cold dark matter models. We show that a self-interacting dark matter
model with a particle mass of roughly 50 GeV annihilating to the mediator
responsible for the strong self-interaction can simultaneously explain all
three observations. The mediator is necessarily unstable and its mass must be
below about 100 MeV in order to lower densities in faint galaxies. If the
mediator decays to electron-positron pairs with a cross section on the order of
the thermal relic value, then we find that these pairs can up-scatter the
interstellar radiation field and produce the observed -ray excess. We
show that this model is compatible with all current constraints and highlight
detectable signatures unique to self-interacting dark matter models.Comment: 6 pages, 4 figure
Triplet-Quadruplet Dark Matter
We explore a dark matter model extending the standard model particle content
by one fermionic triplet and two fermionic quadruplets,
leading to a minimal realistic UV-complete model of electroweakly interacting
dark matter which interacts with the Higgs doublet at tree level via two kinds
of Yukawa couplings. After electroweak symmetry-breaking, the physical spectrum
of the dark sector consists of three Majorana fermions, three singly charged
fermions, and one doubly charged fermion, with the lightest neutral fermion
serving as a dark matter candidate. A typical spectrum exhibits a
large degree of degeneracy in mass between the neutral and charged fermions,
and we examine the one-loop corrections to the mass differences to ensure that
the lightest particle is neutral. We identify regions of parameter space for
which the dark matter abundance is saturated for a standard cosmology,
including coannihilation channels, and find that this is typically achieved for
. Constraints from precision electroweak
measurements, searches for dark matter scattering with nuclei, and dark matter
annihilation are important, but leave open a viable range for a thermal relic.Comment: 27 pages, 6 figures. v2: minor revisions to match published versio
Tying Dark Matter to Baryons with Self-interactions
Self-interacting dark matter (SIDM) models have been proposed to solve the
small-scale issues with the collisionless cold dark matter (CDM) paradigm. We
derive equilibrium solutions in these SIDM models for the dark matter halo
density profile including the gravitational potential of both baryons and dark
matter. Self-interactions drive dark matter to be isothermal and this ties the
core sizes and shapes of dark matter halos to the spatial distribution of the
stars, a radical departure from previous expectations and from CDM predictions.
Compared to predictions of SIDM-only simulations, the core sizes are smaller
and the core densities are higher, with the largest effects in baryon-dominated
galaxies. As an example, we find a core size around 0.5 kpc for dark matter in
the Milky Way, more than an order of magnitude smaller than the core size from
SIDM-only simulations, which has important implications for indirect searches
of SIDM candidates.Comment: 5 pages, 2 figures. v2: sections II and III edited heavily for
clarity of presentation, changes to figure 2 (halo shape), conclusions
unchange
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