Publications (72) View all
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Article: Non-linear evolution of the cosmic neutrino background
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ABSTRACT: We investigate the non-linear evolution of the relic cosmic neutrino background by running large box-size, high resolution N-body simulations. Our set of simulations explore the properties of neutrinos in a reference $\Lambda$CDM model with total neutrino masses between 0.05-0.60 eV in cold dark matter haloes of mass $10^{11}-10^{15}$ $h^{-1}$M$_{\odot}$, over a redshift range $z=0-2$. We compute the halo mass function and show that it is reasonably well fitted by the Sheth-Tormen formula. More importantly, we focus on the CDM and neutrino properties of the density and peculiar velocity fields in the cosmological volume, inside and in the outskirts of virialized haloes. The dynamical state of the neutrino particles depends strongly on their momentum: whereas neutrinos in the low velocity tail behave similarly to CDM particles, neutrinos in the high velocity tail are not affected by the clustering of the underlying CDM component. We find that the neutrino (linear) unperturbed momentum distribution is modified and mass and redshift dependent deviations from the expected Fermi-Dirac distribution are in place both in the cosmological volume and inside haloes. The neutrino density profiles around virialized haloes have been carefully investigated and a simple fitting formula is provided. The neutrino profile, unlike the cold dark matter one, is found to be cored with core size and central density that depend on the neutrino mass, redshift and mass of the halo, for halos of masses larger than $\sim 10^{13.5}h^{-1}$M$_{\odot}$. For lower masses the neutrino profile is best fitted by a simple power-law relation in the range probed by the simulations. Our findings are particularly important in view of upcoming large-scale structure surveys, like Euclid, that are expected to probe the non-linear regime at the percent level with lensing and clustering observations.12/2012; -
Article: Neutrino halos in clusters of galaxies and their weak lensing signature
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ABSTRACT: We study whether non-linear gravitational effects of relic neutrinos on the development of clustering and large-scale structure may be observable by weak gravitational lensing. We compute the density profile of relic massive neutrinos in a spherical model of a cluster of galaxies, for several neutrino mass schemes and cluster masses. Relic neutrinos add a small perturbation to the mass profile, making it more extended in the outer parts. In principle, this non-linear neutrino perturbation is detectable in an all-sky weak lensing survey such as EUCLID by averaging the shear profile of a large fraction of the visible massive clusters in the universe, or from its signature in the general weak lensing power spectrum or its cross-spectrum with galaxies. However, correctly modeling the distribution of mass in baryons and cold dark matter and suppressing any systematic errors to the accuracy required for detecting this neutrino perturbation is severely challenging.Journal of Cosmology and Astroparticle Physics 06/2011; 2011(06):027. · 5.72 Impact Factor -
Article: Photo-z optimization for measurements of the BAO radial scale
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ABSTRACT: Baryon Acoustic Oscillations (BAO) in the radial direction offer a method to directly measure the Universe expansion history, and to set limits to space curvature when combined to the angular BAO signal. In addition to spectroscopic surveys, radial BAO might be measured from accurate enough photometric redshifts obtained with narrow-band filters. We explore the requirements for a photometric survey using Luminous Red Galaxies (LRG) to competitively measure the radial BAO signal and discuss the possible systematic errors of this approach. Using the LRG spectra obtained from SDSS, we find that the optimal system consists of ~ 30 filters of width Δλ/λ ~ 0.02. A S/N>20 is generally necessary at the filters on the red side of the Balmer-break to reach the target photometric accuracy σz = 0.003(1+z) for measuring radial BAO. The presence of outliers can significantly degrade this: in any practical application, being able to efficiently remove outliers may require ancillary observations. We estimate that a 5-year survey in a dedicated telescope with etendue in excess of 60 m2 deg2 would be necessary to obtain a high enough density of galaxies to measure the radial BAO with shot noise smaller than cosmic variance up to z = 0.85. We conclude that spectroscopic surveys have a superior performance than photometric ones for measuring BAO in the radial direction.Journal of Cosmology and Astroparticle Physics 04/2009; 2009(04):008. · 5.72 Impact Factor -
Article: Detection of atmospheric muon neutrinos with the IceCube 9-string detector
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ABSTRACT: The IceCube neutrino detector is a cubic kilometer TeV to PeV neutrino detector under construction at the geographic South Pole. The dominant population of neutrinos detected in IceCube is due to meson decay in cosmic-ray air showers. These atmospheric neutrinos are relatively well understood and serve as a calibration and verification tool for the new detector. In 2006, the detector was approximately 10% completed, and we report on data acquired from the detector in this configuration. We observe an atmospheric neutrino signal consistent with expectations, demonstrating that the IceCube detector is capable of identifying neutrino events. In the first 137.4 days of live time, 234 neutrino candidates were selected with an expectation of 211±76.1(syst)±14.5(stat) events from atmospheric neutrinos.Phys. Rev. D. 07/2007; 76(2). -
Article: Five years of searches for point sources of astrophysical neutrinos with the AMANDA-II neutrino telescope
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ABSTRACT: We report the results of a five-year survey of the northern sky to search for point sources of high energy neutrinos. The search was performed on the data collected with the AMANDA-II neutrino telescope in the years 2000 to 2004, with a live time of 1001 days. The sample of selected events consists of 4282 upward going muon tracks with high reconstruction quality and an energy larger than about 100 GeV. We found no indication of point sources of neutrinos and set 90% confidence level flux upper limits for an all-sky search and also for a catalog of 32 selected sources. For the all-sky search, our average (over declination and right ascension) experimentally observed upper limit Φ0=(E/1 TeV)γ·dΦ/dE to a point source flux of muon and tau neutrino (detected as muons arising from taus) is Φνμ+ν̅ μ0+Φντ+ν̅ τ0=11.1× 10-11 TeV-1 cm-2 s-1, in the energy range between 1.6 TeV and 2.5 PeV for a flavor ratio Φνμ+ν̅ μ0/Φντ+ν̅ τ0=1 and assuming a spectral index γ=2. It should be noticed that this is the first time we set upper limits to the flux of muon and tau neutrinos. In previous papers we provided muon neutrino upper limits only neglecting the sensitivity to a signal from tau neutrinos, which improves the limits by 10% to 16%. The value of the average upper limit presented in this work corresponds to twice the limit on the muon neutrino flux Φνμ+ν̅ μ0=5.5×10-11 TeV-1 cm-2 s-1. A stacking analysis for preselected active galactic nuclei and a search based on the angular separation of the events were also performed. We report the most stringent flux upper limits to date, including the results of a detailed assessment of systematic uncertainties.Phys. Rev. D. 05/2007; 75(10).
