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Science 9 November 2007: Vol. 318. no. 5852, pp. 938 - 943:
Title: Correlation of the Highest-Energy Cosmic Rays with Nearby Extragalactic Objects
Authors: The Pierre Auger Collaboration
Comments: DOI: 10.1126/science.1151124
Using data collected at the Pierre Auger Observatory during the past 3.7 years, we demonstrated a correlation between the arrival directions of cosmic rays with energy above 6 x 10^19 electron volts and the positions of active galactic nuclei (AGN) lying within ~75 megaparsecs. We rejected the hypothesis of an isotropic distribution of these cosmic rays with at least a 99% confidence level from a prescribed a priori test. The correlation we observed is compatible with the hypothesis that the highest-energy particles originate from nearby extragalactic sources whose flux has not been substantially reduced by interaction with the cosmic background radiation. AGN or objects having a similar spatial distribution are possible sources. |
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arXiv:0710.4560 [ps, pdf, other] :
Title: The imprints of primordial non-gaussianities on large-scale structure: scale dependent bias and abundance of virialized objects
Authors: Neal Dalal, Olivier Doré, Dragan Huterer, Alexander Shirokov
Comments: 16 pages, color figures, revtex4. v2: added references and an equation. submitted to PRD
We study the effect of primordial nongaussianity on large-scale structure, focusing upon the most massive virialized objects. Using analytic arguments and N-body simulations, we calculate the mass function and clustering of dark matter halos across a range of redshifts and levels of nongaussianity. We propose a simple fitting function for the mass function valid across the entire range of our simulations. We find pronounced effects of nongaussianity on the clustering of dark matter halos, leading to strongly scale-dependent bias. This suggests that the large-scale clustering of rare objects may provide a sensitive probe of primordial nongaussianity. We very roughly estimate that upcoming surveys can constrain nongaussianity at the level |fNL| <~ 10, competitive with forecasted constraints from the microwave background. |
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arXiv:0711.1105 [ps, pdf, other] :
Title: The fine-grained phase-space structure of Cold Dark Matter halos
Authors: Mark Vogelsberger, Simon D.M. White, Amina Helmi, Volker Springel
Comments: 20 pages, 24 figures, submitted to MNRAS
We present a new and completely general technique for calculating the fine-grained phase-space structure of dark matter throughout the Galactic halo. Our goal is to understand this structure on the scales relevant for direct and indirect detection experiments. Our method is based on evaluating the geodesic deviation equation along the trajectories of individual DM particles. It requires no assumptions about the symmetry or stationarity of the halo formation process. In this paper we study general static potentials which exhibit more complex behaviour than the separable potentials studied previously. For ellipsoidal logarithmic potentials with a core, phase mixing is sensitive to the resonance structure, as indicated by the number of independent orbital frequencies. Regions of chaotic mixing can be identified by the very rapid decrease in the real space density of the associated dark matter streams. We also study the evolution of stream density in ellipsoidal NFW halos with radially varying isopotential shape, showing that if such a model is applied to the Galactic halo, at least $10^5$ streams are expected near the Sun. The most novel aspect of our approach is that general non-static systems can be studied through implementation in a cosmological N-body code. Such an implementation allows a robust and accurate evaluation of the enhancements in annihilation radiation due to fine-scale structure such as caustics. We embed the scheme in the current state-of-the-art code GADGET-3 and present tests which demonstrate that N-body discreteness effects can be kept under control in realistic configurations. |
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arXiv:0710.5073 [ps, pdf, other] :
Title: Signatures of cosmological backreaction
Authors: Nan Li, Dominik J. Schwarz
Comments: 4 pages, 2 figures
We discuss the order of magnitude and signatures of cosmological backreaction as a function of scale. Cosmological backreaction origins from the averaging over a particular and finite domain in the Universe. We show that the effect on the local Hubble rate is significant, about 10% (5%) at 50 (80) Mpc, and identify this effect in existing data. The averaged spatial curvature is relevant for observations up to scales of 200 Mpc.. |
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arXiv:0711.0594 [ps, pdf, other] :
Title: Lines in the cosmic microwave background spectrum from the epoch of cosmological helium recombination
Authors: J.A. Rubino-Martin, J.Chluba, R.A. Sunyaev
Comments: 16 pages, 15 figures. Submitted to A&A
The main goal of this work is to calculate the contributions to the cosmological recombination spectrum due to bound-bound transitions of helium. We show that due to the presence of helium in the early Universe unique features appear in the total cosmological recombination spectrum. These may provide a unique observational possibility to determine the relative abundance of primordial helium, well before the formation of first stars. We include the effect of the tiny fraction of neutral hydrogen atoms on the dynamics of HeII -> HeI recombination at redshifts $z\sim 2500$. As discussed recently, this process significantly accelerates HeII -> HeI recombination, resulting in rather narrow and distinct features in the associated recombination spectrum. In addition this process induces some emission within the hydrogen Lyman-$\alpha$ line, before the actual epoch of hydrogen recombination round $z\sim 1100-1500$. We also show that some of the fine structure transitions of neutral helium appear in absorption, again leaving unique traces in the Cosmic Microwave Background blackbody spectrum, which may allow to confirm our understanding of the early Universe and detailed atomic physics. |
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arXiv:0710.5525 [ps, pdf, other] :
Title: Constraining neutrino masses with the ISW-galaxy correlation function.
Authors: Julien Lesgourgues, Wessel Valkenburg, Enrique Gaztanaga
Comments: 10 pages, 8 figures
Temperature anisotropies in the Cosmic Microwave Background (CMB) are affected by the late Integrated Sachs-Wolfe (lISW) effect caused by any time-variation of the gravitational potential on linear scales. Dark energy is not the only source of lISW, since massive neutrinos induce a small decay of the potential on small scales during both matter and dark energy domination. In this work, we study the prospect of using the cross-correlation between CMB and galaxy density maps as a tool for constraining the neutrino mass. On the one hand massive neutrinos reduce the cross-correlation spectrum because free-streaming slows down structure formation; on the other hand, they enhance it through their change in the effective linear growth. We show that in the observable range of scales and redshifts, the first effect dominates, but the second one is not negligible. We carry out an error forecast analysis by fitting some mock data inspired by the Planck satellite, Dark Energy Survey (DES) and Large Synoptic Survey Telescope (LSST). The inclusion of the cross-correlation data from Planck and LSST increases the sensitivity to the neutrino mass m_nu by 38% (and to the dark energy equation of state w by 83%) with respect to Planck alone. The correlation between Planck and DES brings a far less significant improvement. This method is not potentially as good for detecting m_nu as the measurement of galaxy, cluster or cosmic shear power spectra, but since it is independent and affected by different systematics, it remains potentially interesting if the total neutrino mass is not too small. |
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arXiv:0711.1163 [ps, pdf, other] :
Title: Implications for the Origin of GRB 070201 from LIGO Observations
Authors: B. Abbott et al., for the LIGO Scientific Collaboration
Comments: 10 pages, 8 figures
We analyzed the available LIGO data coincident with GRB 070201, a short duration hard spectrum gamma-ray burst whose electromagnetically determined sky position is coincident with the spiral arms of the Andromeda galaxy (M31). Possible progenitors of such short hard GRBs include mergers of neutron stars or a neutron star and black hole, or soft gamma-ray repeater (SGR) flares. These events can be accompanied by gravitational-wave emission. No plausible gravitational wave candidates were found within a 180 s long window around the time of GRB 070201. This result implies that a compact binary progenitor of GRB 070201, with masses in the range 1 M_sun < m_1 < 3 M_sun and 1 M_sun < m_2 < 40 M_sun, located in M31 is excluded at >99% confidence. Indeed, if GRB 070201 were caused by a binary neutron star merger, we find that D < 3.5 Mpc is excluded, assuming random inclination, at 90% confidence. The result also implies that an unmodeled gravitational wave burst from GRB 070201 most probably emitted less than 4.4 x 10^(-4) M_sun c^2 (7.9 x 10^(50) ergs) in any 100 ms long period within the signal region if the source was in M31 and radiated isotropically at the same frequency as LIGO's peak sensitivity (f ~ 150 Hz). This upper limit does not exclude current models of SGRs at the M31 distance. |
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arXiv:0705.4680 [ps, pdf, other] :
Title: Measuring the dark matter velocity anisotropy in galaxy clusters
Authors: Steen H. Hansen, Rocco Piffaretti
Comments: 10 pages 5 figures 1 table
The Universe contains approximately 6 times more dark matter than normal baryonic matter, and a directly observed fundamental difference between dark matter and baryons would both be significant for our understanding of dark matter structures and provide us with information about the basic characteristics of the dark matter particle. We discuss one distinctive feature of dark matter structures in equilibrium, namely the property that a local dark matter temperature may depend on direction. This is in stark contrast to baryonic gases. We used X-ray observations of two nearby, relaxed galaxy clusters, under the assumptions of hydrostatic equilibrium and identical dark matter and gas temperatures in the outer cluster region, to measure this dark matter temperature anisotropy beta_dm, with non-parametric Monte Carlo methods. We find that beta_dm is greater than the value predicted for baryonic gases, beta_gas=0, at more than 3 sigma confidence. The observed value of the temperature anisotropy is in fair agreement with the results of cosmological N-body simulations and shows that the equilibration of the dark matter particles is not governed by local point-like interactions in contrast to baryonic gases. |
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