* Astronomy

Blobrana · L

RE: Dark matter

Blobrana · L

Scientists of the Cryogenic Dark Matter Search experiment today announced that they have regained the lead in the worldwide race to find the particles that make up dark matter. The CDMS experiment, conducted a half-mile underground in a mine in Soudan, Minn., again sets the worlds best constraints on the properties of dark matter candidates.

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Blobrana · L

An international team of astronomers from French and Canadian institutes has analysed Megacam images from the Canada-France-Hawaii Telescope Legacy Survey. They observed for the first time very weak gravitational lensing effects produced by extremely large cosmic structures of the Universe. The distribution of dark matter inside filaments extending up to 270 million light-years in size provides unprecedented information on the cosmic history of structure formation, properties of the dark Universe and the cosmological parameters that characterise the Universe.

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Blobrana · L

Huge filaments of dark matter have been detected in a survey of thousands of distant galaxies. The discovery supports the idea that dark matter drove the formation of galaxies and larger cosmic structures and resolves a discrepancy in previous studies about how much dark matter the universe contains.
The survey, which is still ongoing, has already covered an area of the sky around 300 times the size of the Full Moon. Astronomers led by Liping Fu of the Institute of Astrophysics in Paris, France, have analysed data gathered by the 340-megapixel MegaCam the largest astronomical camera in the world attached to the 3.6-metre Canada France Hawaii Telescope (CFHT) in Hawaii, US.

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Blobrana · L

A University of British Columbia astronomer with an international team has discovered the largest structures of dark matter ever seen. Measuring 270 million light-years across, these dark matter structures criss-cross the night sky, each spanning an area that is eight times larger than the full moon.

The results are a major leap forward since the presence of a cosmic dark matter web that extends over such large distances has never been observed before - Ludovic Van Waerbeke, an assistant professor in the Dept. of Physics and Astronomy.

To glimpse the unseen structures, the team of French and Canadian scientists X-rayed the dark matter, an invisible web that makes up more than 80 per cent of the mass of the universe.

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Blobrana · L

Title: Very weak lensing in the CFHTLS Wide: Cosmology from cosmic shear in the linear regime
Authors: L. Fu, E. Semboloni, H. Hoekstra, M. Kilbinger, L. van Waerbeke, I. Tereno, Y. Mellier, C. Heymans, J. Coupon, K. Benabed, J. Benjamin, E. Bertin, O. Doré, M. J. Hudson, O. Ilbert, R. Maoli, C. Marmo, H. J. McCracken, B. Ménard

We present an exploration of weak lensing by large-scale structure in the linear regime, using the third-year (T0003) CFHTLS Wide data release. Our results place tight constraints on the scaling of the amplitude of the matter power spectrum sigma_8 with the matter density Omega_m. Spanning 57 square degrees to i'_AB = 24.5 over three independent fields, the unprecedented contiguous area of this survey permits high signal-to-noise measurements of two-point shear statistics from 1 arcmin to 4 degrees. Understanding systematic errors in our analysis is vital in interpreting the results. We therefore demonstrate the percent-level accuracy of our method using STEP simulations, an E/B-mode decomposition of the data, and the star-galaxy cross correlation function. We also present a thorough analysis of the galaxy redshift distribution using redshift data from the CFHTLS T0003 Deep fields that probe the same spatial regions as the Wide fields. We find sigma_8(Omega_m/0.25)^0.64 = 0.785±0.043 using the aperture-mass statistic for the full range of angular scales for an assumed flat cosmology, in excellent agreement with WMAP3 constraints. The largest physical scale probed by our analysis is 85 Mpc, assuming a mean redshift of lenses of 0.5 and a LCDM cosmology. This allows for the first time to constrain cosmology using only cosmic shear measurements in the linear regime. Using only angular scales theta> 85 arcmin, we find sigma_8(Omega_m/0.25)_lin^0.53 = 0.837±0.084, which agree with the results from our full analysis. Combining our results with data from WMAP3, we find Omega_m=0.248±0.019 and sigma_8 = 0.771±0.029.

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Blobrana · L

Title: Cosmological Constraints on Invisible Decay of Dark Matter
Authors: Yan Gong, Xuelei Chen

The cold dark matter may be in a meta-stable state and decays to other particles with a very long lifetime. If the decaying products of the dark matter are weakly interacting, e.g. neutrinos, then it would have little impact on astrophysical processes and is therefore difficult to observe. However, such a decay would affect the expansion history of the Universe because of the change of the equation of state. We utilize a high-quality type Ia supernovae (SN Ia) data set selected from several resent observations and the position of the first peak of the Cosmic Microwave Background (CMB) angular spectrum given by the WMAP three-year data to constrain the dark matter decay-to-neutrino rate \Gamma=\alpha \Gamma_{\chi}, where \alpha is the fraction of the rest mass which gets converted to neutrinos, and \Gamma_{\chi} is the decay width. We find that \Gamma^{-1} > 0.7 x 10³ Gyr at 95.5% confidence level.

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Blobrana · L

Title: How cold is cold dark matter? Small scales constraints from the flux power spectrum of the high-redshift Lyman-alpha forest
Authors: M. Viel, G. D. Becker, J. S. Bolton, M. G. Haehnelt, M. Rauch, W. L. W. Sargent
(Version v2)

We present constraints on the mass of warm dark matter (WDM) particles derived from the Lyman-alpha flux power spectrum of 55 high- resolution HIRES spectra at 2.0 < z < 6.4. From the HIRES spectra, we obtain a lower limit of mwdm > 1.2 keV 2 sigma if the WDM consists of early decoupled thermal relics and mwdm > 5.6 keV (2 sigma) for sterile neutrinos. Adding the Sloan Digital Sky Survey Lyman-alpha flux power spectrum, we get mwdm > 4 keV and mwdm > 28 keV (2 sigma) for thermal relics and sterile neutrinos. These results improve previous constraints by a factor two.

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Blobrana · L

Scientists could have overlooked a new kind of "stuff".
A radical new proposal to explain one of the enduring mysteries of the universe says we are bathed in an entirely new kind of matter, consisting of "unparticles."
The suggestion that the universe contains a novel kind of "stuff" offers a remarkable way to solve the puzzle of dark matter, which has perplexed cosmologists since it was discovered more than 70 years ago.

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Howard Mason Georgi III, born in 1947 in San Bernardino, California, is Harvard College Professor and Mallinckrodt Professor of Physics at Harvard University.
He is best known for early work in Grand Unification and gauge coupling unification within SU(5) and SO(10) groups.

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Blobrana · L

Title: A Search for Dark Matter Annihilation with the Whipple 10m Telescope
Authors: M. Wood, G. Blaylock, S. M. Bradbury, J. H. Buckley, K. L. Byrum, Y. C. K. Chow, W. Cui, I. de la Calle Perez, A. D. Falcone, S. J. Fegan, J. P. Finley, J. Grube, J. Hall, D. Hanna, J. Holder, D. Horan, T. B. Humensky, D. B. Kieda, J. Kildea, A. Konopelko, H. Krawczynski, F. Krennrich, M. J. Lang, S. LeBohec, T. Nagai, R. A. Ong, J. S. Perkins, M. Pohl, J. Quinn, H. J. Rose, G. H. Sembroski, V. V. Vassiliev, R. G. Wagner, S. P. Wakely, T. C. Weekes, A. Weinstein

We present observations of the dwarf galaxies Draco and Ursa Minor, the local group galaxies M32 and M33, and the globular cluster M15 conducted with the Whipple 10m gamma-ray telescope to search for the gamma-ray signature of self-annihilating weakly interacting massive particles (WIMPs) which may constitute astrophysical dark matter (DM). We review the motivations for selecting these sources based on their unique astrophysical environments and report the results of the data analysis which produced upper limits on excess rate of gamma rays for each source. We consider models for the DM distribution in each source based on the available observational constraints and discuss possible scenarios for the enhancement of the gamma-ray luminosity. Limits on the thermally averaged product of the total self-annihilation cross section and velocity of the WIMP, <\sigma v>, are derived using conservative estimates for the magnitude of the astrophysical contribution to the gamma-ray flux. Although these limits do not constrain predictions from the currently favoured theoretical models of supersymmetry (SUSY), future observations with VERITAS will probe a larger region of the WIMP parameter phase space, <\sigma v> and WIMP particle mass (m_\chi).

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