Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session X11: Dark Matter, Dark Energy and Structure |
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Sponsoring Units: DAP Chair: Anze Slosar, Brookhaven National Laboratory Room: Garden 2 |
Tuesday, May 3, 2011 10:45AM - 10:57AM |
X11.00001: The Dark Energy Survey Klaus Honscheid The Dark Energy Survey will employ a powerful instrument, the Dark Energy Camera, and a state-of-the-art data management system on the improved Blanco 4-meter telescope at CTIO to probe the nature of dark energy and the cause of cosmic acceleration. The instrument includes a 520-Megapixel optical imager with red-sensitive CCDs covering a 3 square degree field of view and an active alignment system. Starting in 2012, using 525 nights over 5 years, the survey will image 300 million galaxies over 5000 square degrees to 24th magnitude and several thousand supernovae over a smaller area, using the grizY passbands. The 120-member international collaboration will use these data to probe dark energy using the galaxy cluster abundance, weak gravitational lensing, baryon acoustic oscillations, and supernovae and carry out studies of strong lensing, galaxy evolution, the structure of the Milky Way, and QSOs, among other topics. We will discuss the status of the project, the survey strategy and prospects for cosmological tests. [Preview Abstract] |
Tuesday, May 3, 2011 10:57AM - 11:09AM |
X11.00002: The Dark Energy Survey Camera (DECam) Klaus Honscheid The Dark Energy Survey (DES) is a next generation optical survey aimed at understanding the expansion rate of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the survey, the DES Collaboration is building the Dark Energy Camera (DECam), a 3 square degree, 520 Megapixel CCD camera which will be mounted at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory. The survey will cover 5000 square-degrees of the southern galactic cap with 5 filters (g, r, i, z, Y). DECam will be comprised of 74 250 micron thick fully depleted CCDs: 62 2k x 4k CCDs for imaging and 12 2k x 2k CCDs for guiding and focus. Construction of DECam is nearing completion. In order to verify that the camera meets technical specifications for the Dark Energy Survey and to reduce the time required to commission the instrument on the telescope, we have constructed a full sized ``Telescope Simulator'' and are performing full system testing and integration prior to shipping to CTIO. An overview of the DECam design and the status of the construction and integration tests will be presented. [Preview Abstract] |
Tuesday, May 3, 2011 11:09AM - 11:21AM |
X11.00003: Constraining ultralight dark matter models from observed black hole distributions Ruxandra Bondarescu, Jayashree Balakrishna, Mihai Bondarescu We consider the quantum mechanical collapse of a ball of dust in the context of ultra-light dark matter. In the classical Oppenheimer-Snyder collapse of a ball of dust to a black hole each dust particle is assumed to be infinitely small, infinitely light and to interact only gravitationally with other matter. This approximation is not perfect as infinitely light particles are infinitely large in size and would never be localized within the dust ball or horizon. Ultra-light dark matter particles ($m \sim 10^{-23}$ eV) come close to the attributes classical dust, except that they are so small that quantum effects play an important role. In this talk we reconsider the Oppenheimer-Schneider model without neglecting quantum effects, and explore interesting facts about the Universe. I plan to discuss the smallest black hole that can be formed from these ultralight particles. Once black holes reach this mass they could feed on dark matter and increase in size. This could affect the black hole distribution in that black holes of a certain mass range would be difficult to find. [Preview Abstract] |
Tuesday, May 3, 2011 11:21AM - 11:33AM |
X11.00004: CDM Halos as Bose-Einstein Condensates: from Axions to Repulsive Dark Matter Tanja Rindler-Daller, Paul R. Shapiro In the past two decades, suggestions have appeared in the literature that dark matter (DM) may be in the form of a Bose-Einstein condensate (BEC). The respective particle candidates, which have been shown to form a BEC, can be found at the low end of the DM mass spectrum, ranging from the QCD axion down to extremely-light bosons. In the context of the Gross-Pitaevskii theory of gaseous BECs under self-gravity with varying particle interaction strengths, we derive the respective halo structures and density profiles. BEC halos have flat cores for all particle coupling strengths, in contrast to the cuspy centers of standard CDM halos. We also study the influence of angular momentum, as acquired by tidal-torquing in the early phases of halo formation, and show that vortices can be formed in halo centers in the regime of strong particle interactions, making an initially irrotational fluid having vorticity. Vortices deplete the DM in their cores, which in turn influences the gravitational coupling to the baryons. As a consequence, baryon cooling and condensation, a prerequisite of star formation, may be delayed or suppressed for small-mass halos. [Preview Abstract] |
Tuesday, May 3, 2011 11:33AM - 11:45AM |
X11.00005: ABSTRACT WITHDRAWN |
Tuesday, May 3, 2011 11:45AM - 11:57AM |
X11.00006: Impact of realistic halo velocity distributions on the interpretation of WIMP searches and future experimental designs D. Speller, A. Gamboa, J. Rolla, B. Sadoulet The interpretation of Weakly Interacting Massive Particle search results depends heavily on the assumptions made about the distribution of WIMP velocities in the galactic halo. A Maxwell-Boltzmann distribution with a sharp cutoff is usually assumed, but recent attempts to reconcile the claims of DAMA with the exclusion regions of experiments such as CDMS and Xenon 100 are based on threshold effects expected to arise from inelastic scattering, and may be sensitive to the assumed shape of the tail in the distribution. We are using realistic velocity distributions from recent large-scale halo simulations to evaluate the impact of the assumptions underlying the interpretation of dark matter search results. We are also investigating the effects of spatial and velocity inhomogeneities (streams) expected at the solar radius in these simulations. Our goal is to gain more insight into the instrumental challenges faced by a Dark Matter Observatory: requirements for detector mass, background rejection, the need for multiple targets, and the use and extraction of directional information. [Preview Abstract] |
Tuesday, May 3, 2011 11:57AM - 12:09PM |
X11.00007: Constraints from GRB Observation for Cosmological Models Razieh Behkam, James Rhoads We use Liang-Zhang relation for Gamma Ray Bursts to constrain $\Lambda $ Cold Dark Matter standard cosmology and a particular class of brane cosmology (brane-induced gravity model). With the most probable model being $\Omega _m =0.23$ and $\Omega _\Lambda =0.77$ for flat $\Lambda $CDM cosmology and $\Omega _m =0.18$ and $\Omega _{r_c } =0.17$ for flat brane-induced gravity cosmology, our result is comparable with the result from SNIa observation. With average uncertainty of distance modulus being 0.2771, the two discussed cosmologies are indistinguishable using our current sample of GRB with redshift ranging between 0.1685 and 3.2. We argue that by expanding the sample and adding more low and high redshift GRBs and also with improvement in using GRBs for cosmography, we might be able to distinguish between different cosmological models and tighten the most probable area. [Preview Abstract] |
Tuesday, May 3, 2011 12:09PM - 12:21PM |
X11.00008: Voids as probe of dark energy Esfandiar Alizadeh, Guilhem Lavaux, Rahul Biswas, Benjamin Wandelt Cosmological voids have the potential to be used as probes of the cosmological parameters. I will present our results on how sensitive some properties of voids, i.e. their ellipticies and number counts, are to the equation state of the dark energy. We used the Fisher matrix analysis to forecast the error bars on ``w'' using the void statistics combined with other cosmological probes to argue that the use of voids improves upon other probes with essentially no extra cost. [Preview Abstract] |
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