790 research outputs found

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

The statistical distribution of galaxies is a powerful probe to constrain
cosmological models and gravity. In particular the matter power spectrum $P(k)$
brings information about the cosmological distance evolution and the galaxy
clustering together. However the building of $P(k)$ 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
$P(k)$ from other cosmological models, and for photometric surveys like LSST.
The angular power spectrum $C_\ell(z_1,z_2)$ between two bins located at
redshift $z_1$ and $z_2$ contains the same information than the matter power
spectrum, is free from any cosmological assumption, but the prediction of
$C_\ell(z_1,z_2)$ from $P(k)$ is a costly computation when performed exactly.
The Angpow software aims at computing quickly and accurately the auto
($z_1=z_2$) and cross ($z_1 \neq z_2$) 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
$C_\ell(z_1,z_2)$ comparison with data. We emphasize that the Limber's
approximation, often used to fasten the computation, gives wrong $C_\ell$
values for cross-correlations.Comment: Published in Astronomy & Astrophysic

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

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 $C(\theta; z_1, z_2)$ 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 $C_\ell(z_1, z_2)$ 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 $C(\theta; z_1, z_2)$
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

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 $\theta_{13}$ 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 $\theta_{23}$.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

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

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

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
$\theta_{13}$ and the CP-violating phase $\delta$.Comment: 1+33 pages, 14 figures, Expression of Interest of MEMPHYS projec

### BAORadio : Cartographie 3D de la distribution de gaz H$_I$ dans l'Univers

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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