342 research outputs found
Dark Matter, Shared Asymmetries, and Galactic Gamma Ray Signals
We introduce a novel dark matter scenario where the visible sector and the
dark sector share a common asymmetry. The two sectors are connected through an
unstable mediator with baryon number one, allowing the standard model baryon
asymmetry to be shared with dark matter via semi-annihilation. The present-day
abundance of dark matter is then set by thermal freeze-out of this
semi-annihilation process, yielding an asymmetric version of the WIMP miracle
as well as promising signals for indirect detection experiments. As a proof of
concept, we find a viable region of parameter space consistent with the
observed Fermi excess of GeV gamma rays from the galactic center.Comment: 20+12 pages, 11 figures, 1 table; v2: references added, minor
corrections to CMB bounds; v3: footnotes added for clarification, updated
appendix A, conclusions unchanged, version to appear in JCA
Distorted Neutrino Oscillations From Ultralight Scalar Dark Matter
Cold, ultralight ( eV) bosonic dark matter with a misalignment abundance
can induce temporal variation in the masses and couplings of Standard Model
particles. We find that fast variations in neutrino oscillation parameters can
lead to significantly distorted neutrino oscillations (DiNOs) and yield
striking signatures at long baseline experiments. We study several
representative observables to demonstrate this effect and find that current and
future experiments including DUNE and JUNO are sensitive to a wide range of
viable scalar parameters over many decades in mass reach.Comment: 5+2 pages, 4 figures , 2 appendice
(In)direct Detection of Boosted Dark Matter
We initiate the study of novel thermal dark matter (DM) scenarios where
present-day annihilation of DM in the galactic center produces boosted stable
particles in the dark sector. These stable particles are typically a
subdominant DM component, but because they are produced with a large Lorentz
boost in this process, they can be detected in large volume terrestrial
experiments via neutral-current-like interactions with electrons or nuclei.
This novel DM signal thus combines the production mechanism associated with
indirect detection experiments (i.e. galactic DM annihilation) with the
detection mechanism associated with direct detection experiments (i.e. DM
scattering off terrestrial targets). Such processes are generically present in
multi-component DM scenarios or those with non-minimal DM stabilization
symmetries. As a proof of concept, we present a model of two-component thermal
relic DM, where the dominant heavy DM species has no tree-level interactions
with the standard model and thus largely evades direct and indirect DM bounds.
Instead, its thermal relic abundance is set by annihilation into a subdominant
lighter DM species, and the latter can be detected in the boosted channel via
the same annihilation process occurring today. Especially for dark sector
masses in the 10 MeV-10 GeV range, the most promising signals are electron
scattering events pointing toward the galactic center. These can be detected in
experiments designed for neutrino physics or proton decay, in particular
Super-K and its upgrade Hyper-K, as well as the PINGU/MICA extensions of
IceCube. This boosted DM phenomenon highlights the distinctive signatures
possible from non-minimal dark sectors.Comment: 40 pages, 11 figures, 1 table; v2: references added, appendix B
revised; v3: improved presentation of signal/background, added section 4.4 on
earth attenuation, version to appear in JCAP; v4: typos fixed, appendix B
bounds weakened, conclusions unchange
Boosting (In)direct Detection of Dark Matter
In this thesis, I study the expected direct and indirect detection signals of
dark matter. More precisely, I study three aspects of dark matter; I use
hydrodynamic simulations to extract properties of weakly interacting dark
matter that are relevant for both direct and indirect detection signals, and
construct viable dark matter models with interesting experimental signatures.
First, I analyze the full scale Illustris simulation, and find that Galactic
indirect detection signals are expected to be largely symmetric, while
extragalactic signals are not, due to recent mergers and the presence of
substructure. Second, through the study of the high resolution Milky Way
simulation Eris, I find that metal-poor halo stars can be used as tracers for
the dark matter velocity distribution. I use the Sloan Digital Sky Survey to
obtain the first empirical velocity distribution of dark matter, which weakens
the expected direct detection limits by up to an order of magnitude at masses
GeV. Finally, I expand the weakly interacting dark matter
paradigm by proposing a new dark matter model called boosted dark matter. This
novel scenario contains a relativistic component with interesting hybrid direct
and indirect detection signatures at neutrino experiments. I propose two search
strategies for boosted dark matter, at Cherenkov-based experiments and future
liquid-argon neutrino detectors.Comment: PhD Thesis, MIT, May 2017. 178 Pages, 40 Figure
Empirical Determination of Dark Matter Velocities using Metal-Poor Stars
The Milky Way dark matter halo is formed from the accretion of smaller
subhalos. These sub-units also harbor stars---typically old and
metal-poor---that are deposited in the Galactic inner regions by disruption
events. In this Letter, we show that the dark matter and metal-poor stars in
the Solar neighborhood share similar kinematics due to their common origin.
Using the high-resolution Eris simulation, which traces the evolution of both
the dark matter and baryons in a realistic Milky-Way analog galaxy, we
demonstrate that metal-poor stars are indeed effective tracers for the local,
virialized dark matter velocity distribution. The local dark matter velocities
can therefore be inferred from observations of the stellar halo made by the
Sloan Digital Sky Survey within 4 kpc of the Sun. This empirical distribution
differs from the Standard Halo Model in important ways and suggests that the
bounds on the spin-independent scattering cross section may be weakened for
dark matter masses below 10 GeV. Data from Gaia will allow us to further
refine the expected distribution for the smooth dark matter component, and to
test for the presence of local substructure.Comment: 6 pages, 3 figures + supplementary material; v2: Fig. 3 updated,
minor text revisions, overall conclusions unchanged (journal version
Tevfik Fikrete Hitab:
Taha Toros Arşivi, Dosya No: 98/A Tevfik Fikret. Not: Gazetenin "1001 Çerçeve ve" köşesinde yayımlanmıştır.İstanbul Kalkınma Ajansı (TR10/14/YEN/0033) İstanbul Development Agency (TR10/14/YEN/0033
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