790 research outputs found

    Angpow: a software for the fast computation of accurate tomographic power spectra

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    The statistical distribution of galaxies is a powerful probe to constrain cosmological models and gravity. In particular the matter power spectrum P(k)P(k) brings information about the cosmological distance evolution and the galaxy clustering together. However the building of P(k)P(k) from galaxy catalogues needs a cosmological model to convert angles on the sky and redshifts into distances, which leads to difficulties when comparing data with predicted P(k)P(k) from other cosmological models, and for photometric surveys like LSST. The angular power spectrum Cℓ(z1,z2)C_\ell(z_1,z_2) between two bins located at redshift z1z_1 and z2z_2 contains the same information than the matter power spectrum, is free from any cosmological assumption, but the prediction of Cℓ(z1,z2)C_\ell(z_1,z_2) from P(k)P(k) is a costly computation when performed exactly. The Angpow software aims at computing quickly and accurately the auto (z1=z2z_1=z_2) and cross (z1≠z2z_1 \neq z_2) angular power spectra between redshift bins. We describe the developed algorithm, based on developments on the Chebyshev polynomial basis and on the Clenshaw-Curtis quadrature method. We validate the results with other codes, and benchmark the performance. Angpow is flexible and can handle any user defined power spectra, transfer functions, and redshift selection windows. The code is fast enough to be embedded inside programs exploring large cosmological parameter spaces through the Cℓ(z1,z2)C_\ell(z_1,z_2) comparison with data. We emphasize that the Limber's approximation, often used to fasten the computation, gives wrong CℓC_\ell values for cross-correlations.Comment: Published in Astronomy & Astrophysic

    A direct method to compute the galaxy count angular correlation function including redshift-space distortions

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    In the near future, cosmology will enter the wide and deep galaxy survey area allowing high-precision studies of the large scale structure of the universe in three dimensions. To test cosmological models and determine their parameters accurately, it is natural to confront data with exact theoretical expectations expressed in the observational parameter space (angles and redshift). The data-driven galaxy number count fluctuations on redshift shells, can be used to build correlation functions C(θ;z1,z2)C(\theta; z_1, z_2) on and between shells which can probe the baryonic acoustic oscillations, the distance-redshift distortions as well as gravitational lensing and other relativistic effects. Transforming the model to the data space usually requires the computation of the angular power spectrum Cℓ(z1,z2)C_\ell(z_1, z_2) but this appears as an artificial and inefficient step plagued by apodization issues. In this article we show that it is not necessary and present a compact expression for C(θ;z1,z2)C(\theta; z_1, z_2) that includes directly the leading density and redshift space distortions terms from the full linear theory. It can be evaluated using a fast integration method based on Clenshaw-Curtis quadrature and Chebyshev polynomial series. This new method to compute the correlation functions without any Limber approximation, allows us to produce and discuss maps of the correlation function directly in the observable space and is a significant step towards disentangling the data from the tested models

    Physics potential of the CERN-MEMPHYS neutrino oscillation project

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    We consider the physics potential of CERN based neutrino oscillation experiments consisting of a Beta Beam (BB) and a Super Beam (SPL) sending neutrinos to MEMPHYS, a 440 kt water \v{C}erenkov detector at Frejus, at a distance of 130 km from CERN. The θ13\theta_{13} discovery reach and the sensitivity to CP violation are investigated, including a detailed discussion of parameter degeneracies and systematical errors. For SPL sensitivities similar to the ones of the phase II of the T2K experiment (T2HK) are obtained, whereas the BB may reach significantly better sensitivities, depending on the achieved number of total ion decays. The results for the CERN-MEMPHYS experiments are less affected by systematical uncertainties than T2HK. We point out that by a combination of data from BB and SPL a measurement with antineutrinos is not necessary and hence the same physics results can be obtained within about half of the measurement time compared to one single experiment. Furthermore, it is shown how including data from atmospheric neutrinos in the MEMPHYS detector allows to resolve parameter degeneracies and, in particular, provides sensitivity to the neutrino mass hierarchy and the octant of θ23\theta_{23}.Comment: 32 pages, 17 figures, minor improvements on the text wrt to v2, version to appear in JHE

    Resolving Octant Degeneracy at LBL experiment by combining Daya Bay Reactor Setup

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    Long baseline Experiment (LBL) have promised to be a very powerful experimental set up to study various issues related to Neutrinos. Some ongoing and planned LBL and medium baseline experiments are - T2K, MINOS, NOvA, LBNE, LBNO etc. But the long baseline experiments are crippled due to presence of some parameter degeneracies, like the Octant degeneracy. In this work, we first show the presence of Octant degeneracy in LBL experiments, and then combine it with Daya Bay Reactor experiment, at different values of CP violation phase. We show that the Octant degeneracy in LBNE can be resolved completely with this proposal.Comment: 4 pages, 8 figure

    PARISROC, a Photomultiplier Array Integrated Read Out Chip

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    PARISROC is a complete read out chip, in AMS SiGe 0.35 !m technology, for photomultipliers array. It allows triggerless acquisition for next generation neutrino experiments and it belongs to an R&D program funded by the French national agency for research (ANR) called PMm2: ?Innovative electronics for photodetectors array used in High Energy Physics and Astroparticles? (ref.ANR-06-BLAN-0186). The ASIC (Application Specific Integrated Circuit) integrates 16 independent and auto triggered channels with variable gain and provides charge and time measurement by a Wilkinson ADC (Analog to Digital Converter) and a 24-bit Counter. The charge measurement should be performed from 1 up to 300 photo- electrons (p.e.) with a good linearity. The time measurement allowed to a coarse time with a 24-bit counter at 10 MHz and a fine time on a 100ns ramp to achieve a resolution of 1 ns. The ASIC sends out only the relevant data through network cables to the central data storage. This paper describes the front-end electronics ASIC called PARISROC.Comment: IEEE Nuclear Science Symposium an Medical Imaging Conference (2009 NSS/MIC

    MEMPHYS:A large scale water Cerenkov detector at Fr\'ejus

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    A water \v{C}erenkov detector project, of megaton scale, to be installed in the Fr\'ejus underground site and dedicated to nucleon decay, neutrinos from supernovae, solar and atmospheric neutrinos, as well as neutrinos from a super-beam and/or a beta-beam coming from CERN, is presented and compared with competitor projects in Japan and in the USA. The performances of the European project are discussed, including the possibility to measure the mixing angle θ13\theta_{13} and the CP-violating phase δ\delta.Comment: 1+33 pages, 14 figures, Expression of Interest of MEMPHYS projec

    BAORadio : Cartographie 3D de la distribution de gaz HI_I dans l'Univers

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    3D mapping of matter distribution in the universe through the 21 cm radio emission of atomic hydrogen is a complementary approach to optical surveys for the study of the Large Scale Structures, in particular for measuring the BAO (Baryon Acoustic Oscillation) scale up to redshifts z <~ 3 and constrain dark energy. We propose to carry such a survey through a novel method, called intensity mapping, without detecting individual galaxies radio emission. This method requires a wide band instrument, 100 MHz or larger, and multiple beams, while a rather modest angular resolution of 10 arcmin would be sufficient. The instrument would have a few thousand square meters of collecting area and few hundreds of simultaneous beams. These constraints could be fulfilled with a dense array of receivers in interferometric mode, or a phased array at the focal plane of a large antenna
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