27 research outputs found
Separating astrophysical sources from indirect dark matter signals
Indirect searches for products of dark matter annihilation and decay face the
challenge of identifying an uncertain and subdominant signal in the presence of
uncertain backgrounds. Two valuable approaches to this problem are (1) using
analysis methods which take advantage of different features in the energy
spectrum and angular distribution of the signal and backgrounds, and (2) more
accurate characterization of backgrounds, which allows for more robust
identification of possible signals. These two approaches are complementary and
can be significantly strengthened when used together. I review the status of
indirect searches with gamma rays using two promising targets, the Inner Galaxy
and the Isotropic Gamma-Ray Background. For both targets, uncertainties in the
properties of backgrounds is a major limitation to the sensitivity of indirect
searches. I then highlight approaches which can enhance the sensitivity of
indirect searches using these targets.Comment: 7 pages, 4 figures. Contributed to the National Academy of Sciences'
Dark Matter Sackler Colloquiu
Robust identification of isotropic diffuse gamma rays from Galactic dark matter
Dark matter annihilation in Galactic substructure will produce diffuse
gamma-ray emission of remarkably constant intensity across the sky, making it
difficult to disentangle this Galactic dark matter signal from the
extragalactic gamma-ray background. We show that if Galactic dark matter
contributes a modest fraction of the measured emission in an energy range
accessible to the Fermi Gamma-ray Space Telescope, the energy dependence of the
angular power spectrum of the total measured emission could be used to
confidently identify gamma rays from Galactic dark matter substructure.Comment: 4 pages, 2 figures, added 1 reference, published in PR
Signatures of LCDM substructure in tidal debris
In the past decade, surveys of the stellar component of the Galaxy have
revealed a number of streams from tidally disrupted dwarf galaxies and globular
clusters. Simulations of hierarchical structure formation in LCDM cosmologies
predict that the dark matter halo of a galaxy like the Milky Way contains
hundreds of subhalos with masses of ~10^8 solar masses and greater, and it has
been suggested that the existence of coherent tidal streams is incompatible
with the expected abundance of substructure. We investigate the effects of dark
matter substructure on tidal streams by simulating the disruption of a
self-gravitating satellite on a wide range of orbits in different host models
both with and without substructure. We find that the halo shape and the
specific orbital path more strongly determine the overall degree of disruption
of the satellite than does the presence or absence of substructure, i.e., the
changes in the large-scale properties of the tidal debris due to substructure
are small compared to variations in the debris from different orbits in a
smooth potential. Substructure typically leads to an increase in the degree of
clumpiness of the tidal debris in sky projection, and in some cases a more
compact distribution in line-of-sight velocity. Substructure also leads to
differences in the location of sections of debris compared to the results of
the smooth halo model, which may have important implications for the
interpretation of observed tidal streams. A unique signature of the presence of
substructure in the halo which may be detectable by upcoming surveys is
identified. We conclude, however, that predicted levels of substructure are
consistent with a detection of a coherent tidal stream from a dwarf galaxy.Comment: 15 pages, 13 figures, accepted for publication in ApJ. Matches
accepted versio
Novel Techniques for Decomposing Diffuse Backgrounds
The total anisotropy of a diffuse background composed of two or more sources, such as the Fermi-Large Area Telescope (LAT)-measured gamma-ray background, is set by the anisotropy of each source population and the contribution of each population to the total intensity. The total anisotropy as a function of energy (the anisotropy energy spectrum) will modulate as the relative contributions of the sources change, implying that the anisotropy energy spectrum also encodes the intensity spectrum of each source class. We develop techniques, applicable to any such diffuse background, for unraveling the intensity spectrum of each component source population given a measurement of the total intensity spectrum and the total anisotropy energy spectrum, without introducing a priori assumptions about the spectra of the source classes. We demonstrate the potential of these methods by applying them to example scenarios for the composition of the Fermi-LAT gamma-ray background consistent with current data and feasible within 10 yr of observation
Fermi-LAT gamma-ray anisotropy and intensity explained by unresolved Radio-Loud Active Galactic Nuclei
Radio-loud active galactic nuclei (AGN) are expected to contribute
substantially to both the intensity and anisotropy of the isotropic gamma-ray
background (IGRB). In turn, the measured properties of the IGRB can be used to
constrain the characteristics of proposed contributing source classes. We
consider individual subclasses of radio-loud AGN, including low-,
intermediate-, and high-synchrotron-peaked BL Lacertae objects, flat-spectrum
radio quasars, and misaligned AGN. Using updated models of the gamma-ray
luminosity functions of these populations, we evaluate the energy-dependent
contribution of each source class to the intensity and anisotropy of the IGRB.
We find that collectively radio-loud AGN can account for the entirety of the
IGRB intensity and anisotropy as measured by the Fermi Large Area Telescope
(LAT). Misaligned AGN provide the bulk of the measured intensity but a
negligible contribution to the anisotropy, while high-synchrotron-peaked BL
Lacertae objects provide the dominant contribution to the anisotropy. In
anticipation of upcoming measurements with the Fermi-LAT and the forthcoming
Cherenkov Telescope Array, we predict the anisotropy in the broader energy
range that will be accessible to future observations.Comment: 27 pages, 29 figures. This version matches the published version,
minor changes onl
Sensitivity of CTA to dark matter signals from the Galactic Center
The Galactic Center is one of the most promising targets for indirect detection of dark matter with gamma rays. We investigate the sensitivity of the upcoming Cherenkov Telescope Array (CTA) to dark matter annihilation and decay in the Galactic Center. As the inner density profile of the Milky Way's dark matter halo is uncertain, we study the impact of the slope of the Galactic density profile, inwards of the Sun, on the prospects for detecting a dark matter signal with CTA. Adopting the Ring Method to define the signal and background regions in an ON-OFF analysis approach, we find that the sensitivity achieved by CTA to annihilation signals is strongly dependent on the inner profile slope, whereas the dependence is more mild in the case of dark matter decay. Surprisingly, we find that the optimal choice of signal and background regions is virtually independent of the assumed density profile. For the fiducial case of a Navarro-Frenk-White profile, we find that CTA will be able to probe annihilation cross-sections well below the canonical thermal relic value for dark matter masses from a few tens of GeV up to similar to 5 TeV for annihilation to T^+T^- and will achieve only a slightly weaker sensitivity for annihilation to bb or µ^+µ^-. CTA will improve significantly on current sensitivity to annihilation signals for dark matter masses above similar to 100 GeV, covering parameter space that is complementary to that probed by searches with the Fermi Large Area Telescope. The interpretation of apparent excesses in the measured cosmic-ray electron and positron spectra as signals of dark matter decay will also be testable with CTA observations of the Galactic Center. We demonstrate that both for annihilation and for decay, including spectral information for hard channels (such as µ^+µ^- and Ƭ^+T^- leads to enhanced sensitivity for dark matter masses above m_(DM) similar to 200 GeV
New Sensitivity to Solar WIMP Annihilation using Low-Energy Neutrinos
Dark matter particles captured by the Sun through scattering may annihilate
and produce neutrinos, which escape. Current searches are for the few
high-energy neutrinos produced in the prompt decays of some final states. We
show that interactions in the solar medium lead to a large number of pions for
nearly all final states. Positive pions and muons decay at rest, producing
low-energy neutrinos with known spectra, including nuebar through neutrino
mixing. We demonstrate that Super-Kamiokande can thereby provide a new probe of
the spin-dependent WIMP-proton cross section. Compared to other methods, the
sensitivity is competitive and the uncertainties are complementary.Comment: 5 pages, 4 figure