Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session T7: CMB, Structure Formation, Reionization, Indirect Detection |
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Sponsoring Units: DAP Chair: Corbin Covault, Case Western Reserve University Room: Grand E |
Monday, May 2, 2011 3:30PM - 3:42PM |
T7.00001: Design and Calibration of the QUIET CMB Polarimeter Immanuel Buder QUIET is a large--angular-scale Cosmic Microwave Background (CMB) polarimeter designed to measure the B-mode signal from inflation. The design incorporates a new time-stream ``double-demodulation'' technique, a 1.4-m Mizuguchi--Dragone telescope, natural sky rotation, and frequent boresight rotation to minimize systematic contamination. The levels of contamination in the inflationary signal are below $r=0.1$, the best yet achieved by any B-mode polarimeter. Moreover, QUIET is unique among B-mode polarimeters in using a large focal-plane array of miniaturized High--Electron-Mobility Transistor (HEMT) based coherent detectors. These detectors take advantage of a breakthrough in microwave-circuit packaging to achieve a field sensitivity of $69\,\mu$K$\sqrt{\textrm{s}}$. QUIET has collected $>$ 10,000\,hours of data and recently released results from the first observing season at Q band (43 GHz). Analysis of W-band (95-GHz) data is ongoing. I will describe the Q-band calibration plan which uses a combination of astronomical and artificial sources to convert the raw data into polarization measurements with small and well-understood calibration errors. I will also give a status report on calibration for the upcoming W-band results. [Preview Abstract] |
Monday, May 2, 2011 3:42PM - 3:54PM |
T7.00002: First Results from the Q/U Imaging ExperimenT (QUIET) Jonathan Zwart The Q/U Imaging ExperimenT (QUIET) is a large-angular-scale telescope designed to measure the polarization of the cosmic microwave background from the Atacama Desert, Chile and to place direct, competitive limits on the tensor-to-scalar ratio (which parameterizes primordial inflationary B modes) using solely polarization information. We have used QUIET to observe $\approx$~1000\,sq.~deg.~of low-foreground sky at 43 (Q band) and 95\,GHz (W band) between October 2008 and December 2010, collecting some 10000\,hours of data in that time. The integrity of the Q-band data analysis has been verified with an extensive suite of jackknife tests for nullity, and by comparing results from two independent (and blind) analysis pipelines. I shall give an overview of QUIET and present the first power-spectrum results from the Q-band data set, including the E-mode power spectrum, a limit on the tensor-to-scalar ratio, and the detection of polarized Galactic synchroton emission away from the Galactic plane. [Preview Abstract] |
Monday, May 2, 2011 3:54PM - 4:06PM |
T7.00003: Probing gas dynamics in cluster mergers through the SZ effect Siddharth Malu, Ravi Subrahmanyan, Mark Wieringa, D. Narasimha We present 12mm observations of the bullet cluster from the Australia Telescope Compact Array; in particular, a high angular resolution measurement of the substructure in Sunyaev-Zel'dovich Effect (SZE). We report the first discovery of multiple compact SZ features in a galaxy cluster, as also their peculiar displacement from the X-ray brightness centres. None of these SZ feature centres corresponds to any bright spot in X-ray, optical or lensing maps. This implies that the gaspressure distribution differs significantly from the distributions in gas emission measure, galaxy and dark matter distributions. This has implications for the gas physics and evolution in the cluster merger event. SZE displaced from X-ray centres implies that modeling cluster dynamics is non-trivial; our observations indicate that our current lack of understanding cluster merger astrophysics may be a limitation in modeling cluster SZE contribution to small-angle CMB anisotropy and the cause for difficulties in reconciling recent observations of such anisotropy with structure formation models. [Preview Abstract] |
Monday, May 2, 2011 4:06PM - 4:18PM |
T7.00004: Cosmic Reionization and the End of the Dark Ages Paul R. Shapiro The first billion years of cosmic time witnessed the formation of the first galaxies and stars, whose UV radiation gradually burned through the surrounding intergalactic medium, transforming it from a cold, diffuse gas of neutral atoms to a 10,000 K hot gas of ions and electrons. This ``epoch of reionization'' (EOR) filled space with a patchwork quilt of giant ionized zones and neutral zones, until the ionized zones eventually grew to fill all of space. The EOR is one of the last unexplored windows of cosmic time subject to direct observation, and a crucial missing link in our astronomical confirmation of the current standard theory of cosmology, the Cold Dark Matter model. Towards that end, we have pioneered the large-scale numerical simulation of this phenomenon, to predict a host of observable consequences with which to test the theory, ranging from the redshifted cosmic 21cm background from hydrogen atoms in the neutral zones during the EOR, to the angular fluctuations of the cosmic microwave background introduced when those photons scatter off free electrons in the ionized zones, to the quenching of light from the earliest galaxies when their Lyman alpha emission lines resonantly scatter off the trace of neutral atoms left behind inside the ionized zones. I will report the latest developments. [Preview Abstract] |
Monday, May 2, 2011 4:18PM - 4:30PM |
T7.00005: GAPS: A Novel Indirect Search for Dark Mater S.A. Isaac Mognet The General Anti-Particle Spectrometer is a balloon-born instrument currently under development, with an engineering flight planned for 2011 and a first science flight following in 2014. GAPS will conduct a search for antideuterons in the cosmic ray spectrum below 0.3 GeV/n in energy. If the DM particle is a suppersymmetric neutraleno, previous theoretical work has predicted a much enhanced low-energy anti-deuteron flux beyond that predicted purely by secondary production from cosmic ray propagation. Thus, antideuterons provide a background-free channel to search for evidence of DM, unlike other cosmic-ray antimatter species (p-bar , e+). GAPS will use a large acceptance, high detection efficiency payload flown on an LDB or ULDB-class balloon. The instrument will use a novel exotic atom detection technique not needing a magnet. GAPS will thus have a significantly larger total acceptance than other instruments. [Preview Abstract] |
Monday, May 2, 2011 4:30PM - 4:42PM |
T7.00006: Prototype Flight for the GAPS Experiment, An Indirect Search for Dark Matter Tracy Zhang The General Antiparticle Spectrometer (GAPS) is a balloon-based instrument designed to detect low energy ($<$1.0 GeV$/$n) anti-deuterons in cosmic rays. These anti-deuterons can be signature for neutralino dark matter annihilation, and the low energy spectrum has very little anti-deuteron background. The first GAPS science flight is planned for 2014, and a prototype (pGAPS) will fly in 2011 from Japan. pGAPS is equipped with Si(Li) trackers, a time-of-flight system, on-board readout electronics, and a flight computer. The tracker system consists of three Si(Li) layers, which will operate at -35$^{\circ}$C. The goal is to detect de-excitation X-rays from exotic atoms formed by a stopped anti-deuteron and silicon nucleus. The energy resolution will be 3 keV for these X-ray energies. The time-of-flight (TOF) system consists of three layers of scintillation counters, with each layer consisting of two crossed planes of three counters. Each counter is read out on both ends by photomultiplier tubes. The TOF will have a time resolution better than 500ps and it will also provide charge measurement. The pGAPS flight will demonstrate functionality of the various detector components at balloon altitude 33km and pressure, as well as to test the thermal model implemented in detector cooling. The prototype will also provide a measurement of the antiparticle background level at balloon altitude. [Preview Abstract] |
Monday, May 2, 2011 4:42PM - 4:54PM |
T7.00007: The effect of quantum evaporation of dark matter halos M.V. Medvedev What happens to a particle trapped in a gravitational potential? The answer is obvious: it will remain gravitationally bound forever. In this talk show this is not quite true for a quantum particle. We demonstrate that a stable, trapped particle with flavor mixing can gradually and irreversibly escape -- or ``evaporate'' -- from it. This effect is due to mass eigenstate conversions which occur in interactions (scattering) of mass states with other particles even when the energy exchange between them is vanishing. The evaporation and conversion are quantum effects not related to flavor oscillations, particle decay, quantum tunneling or other well-known processes. Apart from their profound academic interest, these effects should have tremendous implications for cosmology. We demonstrate that the flavor-mixed dark matter model can simultaneously explain two outstanding problems of cosmology, namely (1) the absence of central cusps in dark matter halos deduced from observations and (2) the much smaller number of dwarf halos than the CDM prediction known as the sub-structure problem. We also mention the cosmic neutrino background distortion prediction. [Preview Abstract] |
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