237 research outputs found
Dark Matter and the Baryon Asymmetry
We present a mechanism to generate the baryon asymmetry of the Universe which
preserves the net baryon number created in the Big Bang. If dark matter
particles carry baryon number , and , the 's freeze out at a higher temperature
and have a larger relic density than 's. If m_X \lsi 4.5 B_X GeV and the
annihilation cross sections differ by (10%) or more, this type of
scenario naturally explains the observed . Two
concrete examples are given, one of which can be excluded on observational
grounds
Distinguishing Supersymmetry From Universal Extra Dimensions or Little Higgs Models With Dark Matter Experiments
There are compelling reasons to think that new physics will appear at or
below the TeV-scale. It is not known what form this new physics will take,
however. Although The Large Hadron collider is very likely to discover new
particles associated with the TeV-scale, it may be difficult for it to
determine the nature of those particles, whether superpartners, Kaluza-Klein
modes or other states. In this article, we consider how direct and indirect
dark matter detection experiments may provide information complementary to
hadron colliders, which can be used to discriminate between supersymmetry,
models with universal extra dimensions, and Little Higgs theories. We find
that, in many scenarios, dark matter experiments can be effectively used to
distinguish between these possibilities.Comment: 23 pages, 7 figures, references added in version
The Origin of the Extragalactic Gamma-Ray Background and Implications for Dark-Matter Annihilation
The origin of the extragalactic -ray background (EGB) has been
debated for some time. { The EGB comprises the -ray emission from
resolved and unresolved extragalactic sources, such as blazars, star-forming
galaxies and radio galaxies, as well as radiation from truly diffuse
processes.} This letter focuses on the blazar source class, the most numerous
detected population, and presents an updated luminosity function and spectral
energy distribution model consistent with the blazar observations performed by
the {\it Fermi} Large Area Telescope (LAT). We show that blazars account for
50\,\% of the EGB photons (0.1\,GeV), and that {\it Fermi}-LAT
has already resolved 70\,\% of this contribution. Blazars, and in
particular low-luminosity hard-spectrum nearby sources like BL Lacs, are
responsible for most of the EGB emission above 100\,GeV. We find that the
extragalactic background light, which attenuates blazars' high-energy emission,
is responsible for the high-energy cut-off observed in the EGB spectrum.
Finally, we show that blazars, star-forming galaxies and radio galaxies can
naturally account for the amplitude and spectral shape of the background in the
0.1--820\,GeV range, leaving only modest room for other contributions. This
allows us to set competitive constraints on the dark-matter annihilation cross
section.Comment: On behalf of the Fermi-LAT collaboration. Contact authors: M. Ajello,
D. Gasparrini, M. Sanchez-Conde, G. Zaharijas, M. Gustafsson. Accepted for
publication on ApJ
Section on Prospects for Dark Matter Detection of the White Paper on the Status and Future of Ground-Based TeV Gamma-Ray Astronomy
This is a report on the findings of the dark matter science working group for
the white paper on the status and future of TeV gamma-ray astronomy. The white
paper was commissioned by the American Physical Society, and the full white
paper can be found on astro-ph (arXiv:0810.0444). This detailed section
discusses the prospects for dark matter detection with future gamma-ray
experiments, and the complementarity of gamma-ray measurements with other
indirect, direct or accelerator-based searches. We conclude that any
comprehensive search for dark matter should include gamma-ray observations,
both to identify the dark matter particle (through the charac- teristics of the
gamma-ray spectrum) and to measure the distribution of dark matter in galactic
halos.Comment: Report from the Dark Matter Science Working group of the APS
commissioned White paper on ground-based TeV gamma ray astronomy (19 pages, 9
figures
Complementarity of Galactic radio and collider data in constraining WIMP dark matter models
In this work we confront dark matter models to constraints that may be
derived from radio synchrotron radiation from the Galaxy, taking into account
the astrophysical uncertainties and we compare these to bounds set by
accelerator and complementary indirect dark matter searches. Specifically we
apply our analysis to three popular particle physics models. First, a generic
effective operator approach, in which case we set bounds on the corresponding
mass scale, and then, two specific UV completions, the Z' and Higgs portals. We
show that for many candidates, the radio synchrotron limits are competitive
with the other searches, and could even give the strongest constraints (as of
today) with some reasonable assumptions regarding the astrophysical
uncertainties.Comment: 22 pages, 12 figure
Search for extended gamma-ray emission from the Virgo galaxy cluster with Fermi-LAT
Galaxy clusters are one of the prime sites to search for dark matter (DM)
annihilation signals. Depending on the substructure of the DM halo of a galaxy
cluster and the cross sections for DM annihilation channels, these signals
might be detectable by the latest generation of -ray telescopes. Here
we use three years of Fermi Large Area Telescope (LAT) data, which are the most
suitable for searching for very extended emission in the vicinity of nearby
Virgo galaxy cluster. Our analysis reveals statistically significant extended
emission which can be well characterized by a uniformly emitting disk profile
with a radius of 3\deg that moreover is offset from the cluster center. We
demonstrate that the significance of this extended emission strongly depends on
the adopted interstellar emission model (IEM) and is most likely an artifact of
our incomplete description of the IEM in this region. We also search for and
find new point source candidates in the region. We then derive conservative
upper limits on the velocity-averaged DM pair annihilation cross section from
Virgo. We take into account the potential -ray flux enhancement due to
DM sub-halos and its complex morphology as a merging cluster. For DM
annihilating into , assuming a conservative sub-halo model
setup, we find limits that are between 1 and 1.5 orders of magnitude above the
expectation from the thermal cross section for
. In a more optimistic scenario, we
exclude
for for the same channel. Finally, we
derive upper limits on the -ray-flux produced by hadronic cosmic-ray
interactions in the inter cluster medium. We find that the volume-averaged
cosmic-ray-to-thermal pressure ratio is less than .Comment: 15 pages, 11 figures, 4 tables, accepted for publication in ApJ;
corresponding authors: T. Jogler, S. Zimmer & A. Pinzk
Determining Supersymmetric Parameters With Dark Matter Experiments
In this article, we explore the ability of direct and indirect dark matter
experiments to not only detect neutralino dark matter, but to constrain and
measure the parameters of supersymmetry. In particular, we explore the
relationship between the phenomenological quantities relevant to dark matter
experiments, such as the neutralino annihilation and elastic scattering cross
sections, and the underlying characteristics of the supersymmetric model, such
as the values of mu (and the composition of the lightest neutralino), m_A and
tan beta. We explore a broad range of supersymmetric models and then focus on a
smaller set of benchmark models. We find that by combining astrophysical
observations with collider measurements, mu can often be constrained far more
tightly than it can be from LHC data alone. In models in the A-funnel region of
parameter space, we find that dark matter experiments can potentially determine
m_A to roughly +/-100 GeV, even when heavy neutral MSSM Higgs bosons (A, H_1)
cannot be observed at the LHC. The information provided by astrophysical
experiments is often highly complementary to the information most easily
ascertained at colliders.Comment: 46 pages, 76 figure
Searches for Cosmic-Ray Electron Anisotropies with the Fermi Large Area Telescope
The Large Area Telescope on board the \textit{Fermi} satellite
(\textit{Fermi}-LAT) detected more than 1.6 million cosmic-ray
electrons/positrons with energies above 60 GeV during its first year of
operation. The arrival directions of these events were searched for
anisotropies of angular scale extending from 10 up to
90, and of minimum energy extending from 60 GeV up to 480 GeV. Two
independent techniques were used to search for anisotropies, both resulting in
null results. Upper limits on the degree of the anisotropy were set that
depended on the analyzed energy range and on the anisotropy's angular scale.
The upper limits for a dipole anisotropy ranged from to .Comment: 16 pages, 10 figures, accepted for publication in Physical Review D -
contact authors: M.N. Mazziotta and V. Vasileio
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