Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session G7: Dark Matter: Indirect Searches |
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Sponsoring Units: DAP Chair: James Buckley, Washington University in St. Louis Room: Embassy D |
Sunday, April 1, 2012 8:30AM - 8:42AM |
G7.00001: Search For Dark Matter Satellites Using the Fermi LAT Elliott Bloom, Alex Drlica-Wagner, Louis Stirgari, Ping Wang Numerical simulations based on the $\Lambda$CDM model of cosmology predict a large number of as yet unobserved Galactic dark matter satellites. We report the results of a Large Area Telescope (LAT) search for these satellites via the $\gamma$-ray emission expected from the annihilation of weakly interacting massive particle (WIMP) dark matter. Some dark matter satellites are expected to have hard $\gamma$-ray spectra, finite angular extents, and a lack of counterparts at other wavelengths. We sought to identify LAT sources with these characteristics, focusing on $\gamma$-ray spectra consistent with WIMP annihilation through the $b \bar b$ channel. We found no viable dark matter satellite candidates using one year of data, and we present a framework for interpreting this result in the context of numerical simulations to constrain the velocity-averaged annihilation cross section for a conventional 100 GeV WIMP annihilating through the $b \bar b$ channel. [Preview Abstract] |
Sunday, April 1, 2012 8:42AM - 8:54AM |
G7.00002: Constraints on Dark Matter and Supersymmetry from LAT Observations of Dwarf Galaxies Alex Drlica-Wagner Due to a large mass-to-light ratio and low astrophysical backgrounds, dwarf spheroidal galaxies are considered one of the most promising targets for dark matter searches via gamma rays. The Fermi Large Area Telescope (LAT) Collaboration has recently published robust constraints on the dark matter annihilation cross section from a combined analysis of 10 dwarf spheroidal galaxies observed by the LAT. These constraints can be extended to prototypical dark matter models and dark matter models derived from a phenomenological scan of the Minimal Supersymmetric Standard Model (the pMSSM). [Preview Abstract] |
Sunday, April 1, 2012 8:54AM - 9:06AM |
G7.00003: The VERITAS Dark Matter Science Program Andrew Smith In the cosmological paradigm, Cold Dark Matter (DM) dominates the mass content of the Universe and is present at every scale. Candidates for DM include many extensions of the standard model, with a Weakly Interacting Massive Particle (WIMP) in the mass range from 50 GeV to greater than 10 TeV. The self-annihilation of WIMPs in astrophysical regions of high DM density can produce secondary particles including Very High Energy (VHE, $>$100 GeV) gamma rays with energies up to the DM particle mass. The VERITAS array of Cherenkov telescopes, designed for the detection of VHE gamma rays in the 100 GeV-10 TeV energy range, is an appropriate instrument for the indirect detection of DM. Among the possible astrophysical objects considered to be candidates for indirect DM detection, VERITAS has focused on observations of dwarf spheroidal galaxies (dSphs) of the Local Group, the Milky Way galactic center, and Fermi-LAT unidentified GeV sources. This presentation reports on our extensive observations of these targets and our present exclusion regions obtained on the thermally averaged annihilation cross section of the WIMP derived from these observations. [Preview Abstract] |
Sunday, April 1, 2012 9:06AM - 9:18AM |
G7.00004: Using Exact Velocity Distributions for Galactic Dark Matter Halos in Gamma-Ray Luminosity Calculations Daniel Hunter, Francesc Ferrer Gamma-ray observation is a possible way to measure the spacial distribution of dark matter in galactic halos, but some particle models require knowledge of the velocity distribution to make predictions of the luminosity from self-annihilation. For many halo models, this cannot be found analytically. Even in cases where it can be derived, a Maxwell-Boltzmann distribution is often used for the particle velocity in lieu of the correct distribution. A Maxwell-Boltzmann distribution is only correct, however, for a singular isothermal sphere. Furthermore, the velocity distribution does not have a trivial dependence on position, as is usually assumed when calculating line-of-sight integrals in luminosity formulae. In principle, the interaction rate $\langle \sigma v \rangle$ must be included in this integral (commonly called the `J-factor'). We numerically compute the correct velocity distribution for several halo models and compare luminosity predictions with those found using a Maxwell-Boltzmann distribution. In many cases, the Maxwell-Boltzmann distribution is reasonable, but in others, especially when observing the galactic center, it significantly underestimates the luminosity, implying that the true constraints on dark matter models may be more strict than previously thought. [Preview Abstract] |
Sunday, April 1, 2012 9:18AM - 9:30AM |
G7.00005: Quantum-Coherence on Galactic Scales: New Prospects for Constraining Ultra-Light Particle Dark Matter Tanja Rindler-Daller Various extensions of the standard model of particle physics predict generically the existence of ultra-light bosonic particles with masses ranging from the usual QCD axion down to $10^{-33}$ eV/c$^2$. These particles form a large-scale Bose-Einstein condensate (BEC) within a substantial part of the particle parameter space, and are plausible candidates for part or all of the cold dark matter (CDM) in the universe. While particles in the smallest mass range may leave their imprints only on cosmological scales, there is an interesting mass window between around $10^{-25}$ - $10^{-18}$ eV/c$^2$ for which particles can affect halo structures on the scales of massive to dwarf galaxies in a characteristic way. Thereby, this alternative class of dark matter models may not only resolve the shortcomings of standard CDM on those scales, but also provides a means to constrain those models using astronomical observations of galactic dynamics. We will present an overview of the signatures expected, including our own work on the formation of vortices and their effects in rotating BEC halos. [Preview Abstract] |
Sunday, April 1, 2012 9:30AM - 9:42AM |
G7.00006: Applications of passivated silicon detectors Richard Kyung, Chan Ho Park We can postulate that dark matter are WIMPS, more specifically, Majorana particles called neutralinos floating through space. Upon neutralino-neutralino annihilation, they create a greater burst of other particles into space: these being all kinds of particles including anti-deuterons which are the indications of the existence of dark matter. For the study of the applications of passivated silicon detectors, this paper shows following procedures in two categories. Painting on little pieces of silicon (Polyimid and Boxcar Red) :Took clean paint brush and painted on Polyimid and Boxcar red samples onto little pieces of sample silicon and dried for a certain number of hours in different conditions. Cooling test : usually done in 7 cycles, cool until usually -35 degrees or -40 degrees Celsius with thermoelectric cooler, dry out, evapate the moisture in the fume hood, take pictures with the microscope and check for irregularities every 1, 4 and 7 times. The results show us how the passivated silicon will act in the real experiment--the vacuum chamber and x-rays (from the radioactive source), and different atmospheric pressures simulate what it will be like in space. [Preview Abstract] |
Sunday, April 1, 2012 9:42AM - 9:54AM |
G7.00007: Cosmological Simulations Evidence in Favor of Two-Component Flavor-Mixed Cold Dark Matter M.V. Medvedev Many cold dark matter (CDM) candidates are flavor-mixed particles including a neutralino, an axion, a sterile neutrino and some others. An unusual and rather counter-intuitive property of non-relativistic flavor-mixed particles has recently been discovered: in the process of mass-eigenstate conversions, they can escape (or ``evaporate'') from a gravitational potential even if they are initially trapped in it. Modern CDM cosmology has never accounted for the quantum flavor-mixed nature of the particles. Here we present the results of the state-of-the-art LCDM cosmological simulations, which incorporate flavor-mixing. They demonstrate that a model of two-component flavor-mixed dark matter (2cDM) with small mass-degeneracy provides an excellent fit to astronomical data at both large and small scales. It shows substantial reduction of substructure and softening of central cusps in dark halos whereas the large-scale structure remains intact. This simultaneously resolves two outstanding problems of CDM cosmology known as the ``substructure problem'' and ``core/cusp problem'', yet it does not contradict apparent counter-examples and observational constraints. Thus, these findings evidence in favor of the two-component CDM and advance us tremendously toward unraveling the mystery dark ma [Preview Abstract] |
Sunday, April 1, 2012 9:54AM - 10:06AM |
G7.00008: Dark Matter Density as a function of the Time of Year Orvin Wagner The dark matter density is apparently inversely proportional to the square of the horizontal velocity of dark matter waves on earth. I previously used 25 m/s or less as the velocity of dark matter waves on earth because I only could measure the velocity in springtime as I measured plant communication velocities in the late 1980's etc. In the beginning I measured 25 m/s and less in May and earlier. In Sept. 2011 I measured over 1000 m/s, in late October and early November over 20,000 m/s, in late Dec. and early Jan. 2012 it had dropped to hundreds of m/s. Apparently their is a peak velocity, with minimum dark matter density in the Northern hemisphere, in late October and early November. I attribute the variation to the earth's tilt and orbit location in the dark matter wave standing waves organizing the solar system as described in my Physics Essays article of 1999. Most of the planets appear to be on standing wave nodes with earth apparently always at least partially on an antinode. The earth's tilt and location is apparently critical so that the dark matter density can be large in both hemispheres, at proper times and earth locations, e.g. for plant growth (darkmatterwaves.com). [Preview Abstract] |
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