* Astronomy

Title: Dark Matter and Sterile Neutrinos
Authors: Peter L. Biermann (1,2,3), Faustin Munyaneza (1) ((1) Max Planck Institute for Radioastronomy, Germany, (2) Department of Physics and Astronomy, University of Bonn, Germany, (3) Department of Physics and Astronomy, University of Alabama, Tuscaloosa, USA)

Dark matter has been recognized as an essential part of matter for over 70 years now, and many suggestions have been made, what it could be. Most of these ideas have centred on Cold Dark Matter, particles that are predicted in extensions of standard particle physics, such as supersymmetry. Here we explore the concept that dark matter is sterile neutrinos, particles that are commonly referred to as Warm Dark Matter. Such particles have keV masses, and decay over a very long time, much longer than the Hubble time. In their decay they produce X-ray photons which modify the ionisation balance in the very early universe, increasing the fraction of molecular Hydrogen, and thus help early star formation. Sterile neutrinos may also help to understand the baryon-asymmetry, the pulsar kicks, the early growth of black holes, the minimum mass of dwarf spheroidal galaxies, as well as the shape and smoothness of dark matter halos. As soon as all these tests have been made quantitative in their various parameters, we may focus on the creation mechanism of these particles, and could predict the strength of the sharp X-ray emission line, expected from any large dark matter assembly. A measurement of this X-ray emission line would be definitive proof for the existence of may be called weakly interacting neutrinos, or WINs.

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(old news)
After decades of attempts, astronomers have unveiled the dark side of the Universe.
Dark matter, the ubiquitous yet ethereal stuff filling the cosmos, has been mapped three-dimensionally for the first time by a team of astronomers using a fleet of orbiting and ground-based telescopes. Implementing techniques not even dreamed of when dark matter was first postulated, they have created a map two degrees on a side (roughly 15 times the area of the full Moon) and 6 billion light years deep. The Cosmic Evolution Survey, or COSMOS, reveals the spatial distribution of dark matter stretching back to a time when the Universe was half its present age.

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Title: Kinematics and dynamics of the M51-type galaxy pair NGC 3893/96 (KPG 302)
Authors: Isaura Fuentes-Carrera (IAG-USP, Brazil), Margarita Rosado (IA-UNAM, Mexico), Philippe Amram (LAM, France), Heikki Salo, Eija Laurikainen (University of Oulu, Finland)

We study the kinematics and dynamics of the M51-type interacting galaxy pair KPG 302 (NGC 3893/96). We analyse the distribution of the dark matter (DM) halo of the main galaxy in order to explore possible differences between DM halos of "isolated" galaxies and those of galaxies belonging to a pair. The velocity field of each galaxy was obtained using scanning Fabry-Perot interferometry. A two-dimensional kinematic and dynamical analysis of each galaxy and the pair as a whole is done emphasizing the contribution of circular and non-circular velocities. Non-circular motions can be traced on the rotation curves of each galaxy allowing us to differentiate between motions associated to particular features and motions that reflect the global mass distribution of the galaxy. For the main galaxy of the pair, NGC 3893, optical kinematic information is complemented with HI observations from the literature to build a multi-wavelength rotation curve. We try to fit this curve with a mass-distribution model using different DM halos. We find that the multi-wavelength rotation curve of NGC 3893, "cleaned" from the effect of non-circular motions, cannot be fitted neither by a pseudo-isothermal nor by a NFW DM halo.

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Title: First limits on WIMP nuclear recoil signals in ZEPLIN-II: a two phase xenon detector for dark matter detection
Authors: G. J. Alner, H. M. Araujo, A. Bewick, C. Bungau, B. Camanzi, M. J. Carson, R. J. Cashmore, H. Chagani, V. Chepel, D. Cline, D. Davidge, J. C. Davies, E. Daw, J. Dawson, T. Durkin, B. Edwards, T. Gamble, J. Gao, C. Ghag, A. S. Howard, W. G. Jones, M. Joshi, E. V. Korolkova, V. A. Kudryavtsev, T. Lawson, V. N. Lebedenko, J. D. Lewin, P. Lightfoot, A. Lindote, I. Liubarsky, M. I. Lopes, R. Luscher, P. Majewski, K Mavrokoridis, J. E. McMillan, B. Morgan, D. Muna, A. St.J. Murphy, F. Neves, G. G. Nicklin, W. Ooi, S. M. Paling, J. Pinto da Cunha, S. J. S. Plank, R. M. Preece, J. J. Quenby, M. Robinson, F. Sergiampietri, C. Silva, V. N. Solovov, N. J. T. Smith, P. F. Smith, N. J. C. Spooner, T. J. Sumner, C. Thorne, D. R. Tovey, E. Tziaferi, R. J. Walker, H. Wang, J. White, F. L. H. Wolfs

Results are presented from the first underground data run of ZEPLIN-II, a 31 kg two phase xenon detector developed to observe nuclear recoils from hypothetical weakly interacting massive dark matter particles. Discrimination between nuclear recoils and background electron recoils is afforded by recording both the scintillation and ionisation signals generated within the liquid xenon, with the ratio of these signals being different for the two classes of event. This ratio is calibrated for different incident species using an AmBe neutron source and Co-60 gamma-ray sources. From our first 31 live days of running ZEPLIN-II, the total exposure following the application of fiducial and stability cuts was 225 kgxdays. A background population of radon progeny events was observed in this run, arising from radon emission in the gas purification getters, due to radon daughter ion decays on the surfaces of the walls of the chamber. An acceptance window, defined by the neutron calibration data, of 50% nuclear recoil acceptance between 5 keVee and 20 keVee, had an observed count of 29 events, with a summed expectation of 28.6±4.3 gamma-ray and radon progeny induced background events. These figures provide a 90% c.l. upper limit to the number of nuclear recoils of 10.4 events in this acceptance window, which converts to a WIMP-nucleon spin-independent cross-section with a minimum of 6.6x10^-7 pb following the inclusion of an energy dependent, calibrated, efficiency. A second run is currently underway in which the radon progeny will be eliminated, thereby removing the background population, with a projected sensitivity of 2x10^-7 pb for similar exposures as the first run.

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