7,790 research outputs found

    Analytic model for galaxy and dark matter clustering

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    We investigate an analytic model to compute nonlinear power spectrum of dark matter, galaxies and their cross-correlation. The model is based on Press-Schechter halos, which cluster and have realistic dark matter profiles. The total power spectrum is a sum of two contributions, one from correlations betwen the halos and one from correlations within the same halo. We show that such a model can give dark matter power spectra which match well with the results of N-body simulations, provided that concentration parameter decreases with the halo mass. Galaxy power spectrum differs from dark matter power spectrum because pair weighted number of galaxies increases less rapidly than the halo mass, as predicted by theoretical models and observed in clusters. In this case the resulting power spectrum becomes a power law with the slope closed to the observed. Such a model also predicts a later onset of nonlinear clustering compared to the dark matter, which is needed to reconcile the CDM models with the data. Generic prediction of this model is that bias is scale dependent and nonmonotonic. For red or elliptical galaxies bias in power spectrum may be scale dependent even on very large scales. Our predictions for galaxy-dark matter correlations, which can be observed through the galaxy-galaxy lensing, show that these cannot be interpreted simply as an average halo profile of a typical galaxy, because different halo masses dominate at different scales and because larger halos host more than one galaxy. We discuss the prospects of using cross-correlations in combination with galaxy clustering to determine the dark matter power spectrum (ABRIDGED).Comment: 16 pages, 7 figures, submitted to Phys. Rev.

    Gravitational vacuum energy in our recently accelerating universe

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    We review current observations of the homogeneous cosmological expansion which, because they measure only kinematic variables, cannot determine the dynamics driving the recent accelerated expansion. The minimal fit to the data, the flat ΛCDM\Lambda CDM model, consisting of cold dark matter and a cosmological constant, interprets 4Λ4\Lambda geometrically as a classical spacetime curvature constant of nature, avoiding any reference to quantum vacuum energy. (The observed Uehling and Casimir effects measure forces due to QED vacuum polarization, but not any quantum material vacuum energies.) An Extended Anthropic Principle, that Dark Energy and Dark Gravity be indistinguishable, selects out flat ΛCDM\Lambda CDM. Prospective cosmic shear and galaxy clustering observations of the growth of fluctuations are intended to test whether the 'dark energy' driving the recent cosmological acceleration is static or moderately dynamic. Even if dynamic, observational differences between an additional negative-pressure material component within general relativity (Dark Energy) and low-curvature modifications of general relativity (Dark Gravity) will be extremely small.Comment: 3 pages, from Proceedings of the Casimir Workshop, to be published by IOP in Journal of Physics Conference Serie

    Isotropy in the two-point angular correlation function of the CMB

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    We study the directional dependence of the angular two-point correlation function in maps of the cosmic microwave background (CMB). We propose two new statistics, one which measures the correlation of each point in the sky with a ring of points separated angle theta away, and a second that measures the missing angular correlation above 60 degrees as a function of direction. Using these statistics, we find that most of the low power in cut-sky maps measured by the WMAP experiment comes from unusually low contributions from the directions of the lobes of the quadrupole and the octupole. These findings may aid a future explanation of why the CMB exhibits low power at large angular scales.Comment: 9 pages; adjusted format, edited captions, and added reference

    Financing Marine Conservation: A Menu of Options

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    This guide describes over 30 mechanisms for financing the conservation of marine biodiversity, both within and outside of MPAs. Its main purpose is to familiarize conservation professionals i.e., the managers and staff of government conservation agencies, international donors, and nongovernmental organizations (NGOs) with a menu of options for financing the conservation of marine and coastal biodiversity. A number of economic incentive mechanisms for marine conservation (as contrasted with revenue-raising mechanisms) are also presented in section 5 (on Real Estate and Development Rights) and section 6 (on Fishing Industry Revenues). Each section provides a description of the financing mechanism and examples showing how the mechanism has been used to finance marine conservation. In some cases, even though a mechanism may have only been used to finance terrestrial conservation, it has been included in this guide because of its potential to also serve as a new source of funding for marine conservation. This guide is not intended to provide detailed instructions on how to establish and implement each of the different conservation financing mechanisms. Instead references are provided at the end of each section for sources of additional information about each of the mechanisms described. Citations to specific references are also included in the text in parentheses

    Ultra-Light Dark Matter in Ultra-Faint Dwarf Galaxies

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    Cold Dark Matter (CDM) models struggle to match the observations at galactic scales. The tension can be reduced either by dramatic baryonic feedback effects or by modifying the particle physics of CDM. Here, we consider an ultra-light scalar field DM particle manifesting a wave nature below a DM particle mass-dependent Jeans scale. For DM mass m1022eVm\sim10^{-22}{\rm eV}, this scenario delays galaxy formation and avoids cusps in the center of the dark matter haloes. We use new measurements of half-light mass in ultra-faint dwarf galaxies Draco II and Triangulum II to estimate the mass of the DM particle in this model. We find that if the stellar populations are within the core of the density profile then the data are in agreement with a wave dark matter model having a DM particle with m3.75.6×1022eVm\sim 3.7-5.6\times 10^{-22}{\rm eV}. The presence of this extremely light particle will contribute to the formation of a central solitonic core replacing the cusp of a Navarro-Frenk-White profile and bringing predictions closer to observations of cored central density in dwarf galaxies.Comment: matching version accepted by MNRA

    Dark Matter Debris Flows in the Milky Way

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    We show that subhalos falling into the Milky Way create a flow of tidally-stripped debris particles near the galactic center with characteristic velocity behavior. In the Via Lactea-II N-body simulation, this unvirialized component constitutes a few percent of the local density and has velocities peaked at 340 km/s in the solar neighborhood. Such velocity substructure has important implications for surveys of low-metallicity stars, as well as direct detection experiments sensitive to dark matter with large scattering thresholds.Comment: 4 pages, 3 figures; v2 includes new plots illustrating the radial and tangential velocities of non-debris particles; v3 includes some additional minor edit