Munch: Monday, January 22, 2007

                               


 

 WHERE: 6TH FLOOR CONFERENCE ROOM
WHEN  : 12:30, MONDAY

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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       Munch Archive

Bound on the Dark Matter Density in the Solar System from Planetary Motions astro-ph/0701542 (suggested by Scott)

Authors: J.-M. Frère, F.-S. Ling, G. Vertongen
Comments: 7 pages, 1 figure
Report-no: ULB-TH/07-04
High precision planet orbital data extracted from direct observation, spacecraft explorations and laser ranging techniques enable to put a strong constraint on the maximal dark matter density of a spherical halo centered around the Sun. The maximal density at Earth's location is of the order $10^5$ ${\rm GeV/cm^3}$ and shows only a mild dependence on the slope of the halo profile, taken between 0 and -2. This bound is somewhat better than that obtained from the perihelion precession limits.

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The ground-state of General Relativity and Dark Matter                                 hep-th/0701169 (suggested by Mark)

Authors: Maximo Banados
Comments: 4 pages, two column, no figures
We suggest a limit of Einstein equations which incorporates the state g_{\mu\nu}=0 as a solution. The large scale behavior of this theory has unusual asymptotics. For a spherical source, the velocity profile for circular motions is of the form observed in galaxies. For FRW cosmologies, the Friedman equation contains an additional contribution in the matter sector. These examples suggest that taking into account the ground-state g_{\mu\nu}=0 leads to a theory with the correct large scale behavior, without adding extra dark matter.

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Imprints of a Primordial Preferred Direction on the Microwave Background astro-ph/0701357  (suggested by Dan)

Authors: Lotty Ackerman, Sean M. Carroll, Mark B. Wise
Comments: 7 pages, no figures
Report-no: CALT-68-2626
Rotational invariance is a well-established feature of low-energy physics. Violations of this symmetry must be extremely small today, but could have been larger in earlier epochs. In this paper we examine the consequences of a small breaking of rotational invariance during the inflationary era when the primordial density fluctuations were generated. Assuming that a fixed-norm vector picked out a preferred direction during the inflationary era, we explore the imprint it would leave on the cosmic microwave background anisotropy, and provide explicit formulas for the expected amplitudes $<a_{lm}a_{l'm'}^*>$ of the spherical-harmonic coefficients. We suggest that it is natural to expect that the imprint on the primordial power spectrum of a preferred spatial direction is approximately scale-invariant, and examine a simple model in which this is true.

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First results from a Dark Matter search with liquid Argon at 87 K in the Gran Sasso Underground Laboratory  astro-ph/070128  (suggested by Dan)

Authors: P. Benetti, R. Acciarri, F. Adamo, B. Baibussinov, M. Baldo-Ceolin, M. Belluco, F. Calaprice, E. Calligarich, M. Cambiaghi, F. Carbonara, F. Cavanna, S. Centro, A.G. Cocco, F. Di Pompeo, N. Ferrari, G. Fiorillo, C. Galbiati, V. Gallo, L. Grandi, A. Ianni, G. Mangano, G. Meng, C. Montanari, O. Palamara, L. Pandola, F. Pietropaolo, G.L. Raselli, M. Rossella, C. Rubbia, A. M. Szelc, S. Ventura, C. Vignoli
Comments: 26 pages, 8 figures, submitted to astroparticle physics
A new method of searching for dark matter in the form of weakly interacting massive particles (WIMP) has been developed with the direct detection of the low energy nuclear recoils observed in a massive target (ultimately many tons) of ultra pure Liquid Argon at 87 K. A high selectivity for Argon recoils is achieved by the simultaneous observation of both the VUV scintillation luminescence and of the electron signal surviving columnar recombination, extracted through the liquid-gas boundary by an electric field. First physics results from this method are reported, based on a small 2.3 litre test chamber filled with natural Argon and an accumulated fiducial exposure of about 100 kg x day, supporting the future validity of this method with isotopically purified 40Ar and for a much larger unit presently under construction with correspondingly increased sensitivities.

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Ultra-high energy cosmic ray investigations by means of EAS muon density measurements  astro-ph/0701324  (suggested by Scott)

Authors: N.S. Barbashina, A.G. Bogdanov, D.V. Chernov, A.N. Dmitrieva, D.M. Gromushkin, V.V. Kindin, R.P. Kokoulin, K.G. Kompaniets, G. Mannocchi, A.A. Petrukhin, O. Saavedra, V.V. Shutenko, D.A. Timashkov, G. Trinchero, I.I. Yashin
Comments: 7 pages, 7 figures. Presented at CRIS-2006, Catania, Italy, May 29 - June 2, 2006. Accepted for publication in Nucl. Phys. B (Proc. Suppl.)
A new approach to investigations of ultra-high energy cosmic rays based on the ground-level measurements of the spectra of local density of EAS muons at various zenith angles is considered. Basic features of the local muon density phenomenology are illustrated using a simple semi-analytical model. It is shown that muon density spectra are sensitive to the spectrum slope, primary composition, and to the features of hadronic interaction. New experimental data on muon bundles at zenith angles from 30 degrees to horizon obtained with the coordinate detector DECOR are compared with CORSIKA-based simulations. It is found that measurements of muon density spectra in inclined EAS give possibility to study characteristics of primary cosmic ray flux in a very wide energy range from 10^15 to 10^19 eV.

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COSMOS: 3D weak lensing and the growth of structure  astro-ph/0701480  (suggested by Scott)

Authors: Richard Massey, Jason Rhodes, Alexie Leauthaud, Peter Capak, Richard Ellis, Anton Koekemoer, Alexandre Refregier, Nick Scoville, James E. Taylor, Justin Albert, Joel Berge, Catherine Heymans, David Johnston, Jean-Paul Kneib, Yannick Mellier, Bahram Mobasher, Elisabetta Semboloni, Patrick Shopbell, Lidia Tasca, Ludovic Van Waerbeke
Comments: 21 pages, 15 figures. Resubmitted to ApJ, including improvements suggested by a referee
We present a three dimensional cosmic shear analysis of the Hubble Space Telescope COSMOS survey, the largest ever optical imaging program performed in space. We have measured the shapes of galaxies for the tell-tale distortions caused by weak gravitational lensing, and traced the growth of that signal as a function of redshift. Using both 2D and 3D analyses, we measure cosmological parameters Omega_m, the density of matter in the universe, and sigma_8, the normalization of the matter power spectrum. The introduction of redshift information tightens the constraints by a factor of three, and also reduces the relative sampling (or "cosmic") variance compared to recent surveys that may be larger but are only two dimensional. From the 3D analysis, we find sigma_8*(Omega_m/0.3)^-0.44=0.866+^0.085_-0.068 at 68% confidence limits, including both statistical and potential systematic sources of error in the total budget. Indeed, the absolute calibration of shear measurement methods is now the dominant source of uncertainty. Assuming instead a baseline cosmology to fix the geometry of the universe, we have measured the growth of structure on both linear and non-linear physical scales. Our results thus demonstrate a proof of concept for tomographic analysis techniques that have been proposed for future weak lensing surveys by a dedicated wide-field telescope in space.

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Can large-scale structure probe CMB-constrained non-Gaussianity?        astro-ph/0701131 (suggested by Emiliano)

Authors: X. Kang, P. Norberg, J. Silk
Comments: 5 Pages, 5 Figures; accepted for publication in MNRAS
The first year Wilkinson Microwave Anisotropy Probe (WMAP) set quantitative constraints on the amplitude of any primordial non-Gaussianity. We run a series of dark matter-only N-body simulations with the WMAP constraints to investigate the effect of the presence of primordial non-Gaussianity on large scale structures. The model parameters can be constrained using the observations of protoclusters associated with Ly-$\alpha$ emitters at high redshift ($2 \leq z \leq 4$), assuming the galaxy velocity bias can be modelled properly. High redshift structure formation potentially provides a more powerful test of possible primordial non-Gaussianity than does the CMB, albeit on smaller scales. Another constraint is given by the local galaxy density probability distribution function (PDF), as mapped by the 2 degree Field Galaxy Redshift Survey (2dFGRS). The PDF of 2dFGRS \lstar galaxies is substantially higher than the standard model predictions and requires either a non-negligible bias between galaxy and dark matter on $\sim 12$~\hmpc scales or a stronger non-Gaussianity than allowed by the WMAP year one data. The latter interpretation is preferred since second-order bias corrections are negative. With a lower normalisation of the power spectrum fluctuations, sigma_8=0.74, as favoured by the WMAP 3 year data, the discrepancy between the Gaussian model and the data is even larger.

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Dark matter from late decays and the small-scale structure problems         hep-ph/0701007 (suggested by Dan)

Authors: Torsten Bringmann, Francesca Borzumati, Piero Ullio
Comments: 15 pages revtex4 style; 10 figures
The generation of dark matter in late decays of quasi-stable massive particles has been proposed as a viable framework to address the excess of power found in numerical N-body simulations for cold dark matter cosmologies. We identify a convenient set of variable to illustrate which requirements need to be satisfied in any generic particle physics model to address the small scale problems and fulfill other astrophysical constraints. We re-examine the role of gravitinos and Kaluza-Klein gravitons in this context and find them disfavoured as a solution to the small-scale problems in case they are DM candidates generated in the decay of thermally produced WIMPs. We propose right-handed sneutrinos and right-handed Kaluza-Klein neutrinos as alternatives. We find that they are viable dark matter candidates, but that they can contribute to a solution of the small scale problems only in case the associated Dirac neutrino mass term appears as a subdominant contribution in the neutrino mass matrix.

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Dark energy from cosmological neutrino condensation                                astro-ph/0701212 (suggested by Scott)

Authors: H. J. de Vega
Comments: 25 pages, 2 figures
We show here that cosmological neutrino condensation provides a continuous energy distribution able to reproduce the observed dark energy. The neutrino evolution is solved as a field theory initial value problem in cosmological spacetime for times after neutrino decoupling. Physical quantities are subtracted in order to eliminate ultraviolet divergences. The subtractions respect the symmetries of the theory and we normalize them such that the physical quantities are zero in Minkowski space-time.The lightest neutrino mass has to be 0.0033 eV for Dirac neutrinos [and 0.0039 eV for Majorana neutrinos] in order to reproduce the observed dark energy.The two heavier neutrinos should annihilate with their respective anti-neutrinos in the time scale of the age of the universe. We find a dark matter equation of state with a logarithmic dependence in the redshift w(z) = -1 - 1/\{3 [21.8 - log(1+z)]} and w(0) = -1.015...These formulas only depend on the ratio of the neutrino temperatures at decoupling and today. Dark energy arises from neutrino condensation in FRW cosmological space-time in an analogous way to the Casimir effect in Minkowski space-time with non-trivial boundaries.

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Hints of Isocurvature Perturbations in the Cosmic Microwave Background  astro-ph/0611917 (suggested by Pasquale)

Authors: Reijo Keskitalo (HIP and Helsinki U.), Hannu Kurki-Suonio (Helsinki U.), Vesa Muhonen (HIP and Helsinki U.), Jussi Valiviita (ICG, Portsmouth)
Comments: 4 pages, 2 figures, revtex4 format
Report-no: HIP-2006-52/TH, ICG 06/43
The improved data on the cosmic microwave background (CMB) anisotropy allows a better determination of the adiabaticity of the primordial perturbation. Interestingly, we find that the CMB favors a significant contribution of a primordial isocurvature mode where the entropy perturbation is positively correlated with the primordial curvature perturbation and has a large spectral index (n_iso ~ 3). With 4 additional parameters we obtain a better fit to the CMB data by \Delta\chi^2 = 9.4 compared to an adiabatic model. At more than 95% C.L., the nonadiabatic contribution to the CMB temperature variance is nonzero; indeed positive. For the best-fit model it is 4%.

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Photonic Astronomy and Quantum Optics  astro-ph/0701220  (suggested by Jeter)

Authors: Dainis Dravins
Comments: Review; 32 pages, 15 figures, 167 references. Book chapter to appear in: D.Phelan, O.Ryan & A.Shearer, eds.: High Time Resolution Astrophysics (Astrophysics and Space Science Library, Springer, 2007). The original publication will be available at www.springerlink.com
Quantum optics potentially offers an information channel from the Universe beyond the established ones of imaging and spectroscopy. All existing cameras and all spectrometers measure aspects of the first-order spatial and/or temporal coherence of light. However, light has additional degrees of freedom, manifest in the statistics of photon arrival times, or in the amount of photon orbital angular momentum. Such quantum-optical measures may carry information on how the light was created at the source, and whether it reached the observer directly or via some intermediate process. Astronomical quantum optics may help to clarify emission processes in natural laser sources and in the environments of compact objects, while high-speed photon-counting with digital signal handling enables multi-element and long-baseline versions of the intensity interferometer. Time resolutions of nanoseconds are required, as are large photon fluxes, making photonic astronomy very timely in an era of large telescopes.

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