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 $B_X$, and $\sigma^{\rm annih}_{\bar{X}} < \sigma^{\rm annih}_{X}$, the $\bar{X}$'s freeze out at a higher temperature and have a larger relic density than $X$'s. If m_X \lsi 4.5 B_X GeV and the annihilation cross sections differ by $\mathcal{O}$(10%) or more, this type of scenario naturally explains the observed $\Omega_{DM} \approx 5 \Omega_b$. 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 $\gamma$-ray background (EGB) has been debated for some time. { The EGB comprises the $\gamma$-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$^{+12}_{-11}$\,\% of the EGB photons ($>$0.1\,GeV), and that {\it Fermi}-LAT has already resolved $\sim$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 $\gamma$-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 $\gamma$-ray flux enhancement due to DM sub-halos and its complex morphology as a merging cluster. For DM annihilating into $b\overline{b}$, 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 $m_{\mathrm{DM}}\lesssim100\,\mathrm{GeV}$. In a more optimistic scenario, we exclude $\langle \sigma v \rangle\sim3\times10^{-26}\,\mathrm{cm^{3}\,s^{-1}}$ for $m_{\mathrm{DM}}\lesssim40\,\mathrm{GeV}$ for the same channel. Finally, we derive upper limits on the $\gamma$-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 $\sim6\%$.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 $\sim$ 10 $^\circ$ up to 90$^\circ$, 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 $\sim0.5$ to $\sim10$.Comment: 16 pages, 10 figures, accepted for publication in Physical Review D - contact authors: M.N. Mazziotta and V. Vasileio