12,299 research outputs found
On the recovery of ISW fluctuations using large-scale structure tracers and CMB temperature and polarization anisotropies
In this work we present a method to extract the signal induced by the
integrated Sachs-Wolfe (ISW) effect in the cosmic microwave background (CMB).
It makes use of the Linear Covariance-Based filter introduced by Barreiro et
al., and combines CMB data with any number of large-scale structure (LSS)
surveys and lensing information. It also exploits CMB polarization to reduce
cosmic variance. The performance of the method has been thoroughly tested with
simulations taking into account the impact of non-ideal conditions such as
incomplete sky coverage or the presence of noise. In particular, three galaxy
surveys are simulated, whose redshift distributions peak at low (), intermediate () and high redshift (). The
contribution of each of the considered data sets as well as the effect of a
mask and noise in the reconstructed ISW map is studied in detail. When
combining all the considered data sets (CMB temperature and polarization, the
three galaxy surveys and the lensing map), the proposed filter successfully
reconstructs a map of the weak ISW signal, finding a perfect correlation with
the input signal for the ideal case and around 80 per cent, on average, in the
presence of noise and incomplete sky coverage. We find that including CMB
polarization improves the correlation between input and reconstruction although
only at a small level. Nonetheless, given the weakness of the ISW signal, even
modest improvements can be of importance. In particular, in realistic
situations, in which less information is available from the LSS tracers, the
effect of including polarisation is larger. For instance, for the case in which
the ISW signal is recovered from CMB plus only one survey, and taking into
account the presence of noise and incomplete sky coverage, the improvement in
the correlation coefficient can be as large as 10 per cent.Comment: 17 pages, 15 figures, accepted for publication in MNRA
Molecular kinetics of solid and liquid CHCl
We present a detailed analysis of the molecular kinetics of CHCl in a
range of temperatures covering the solid and liquid phases. Using nuclear
quadrupolar resonance we determine the relaxation times for the molecular
rotations in solid at pre-melting conditions. Molecular dynamics simulations
are used to characterize the rotational dynamics in the solid and liquid phases
and to study the local structure of the liquid in terms of the molecular
relative orientations. We find that in the pre-melting regime the molecules
rotate about the C-H bond, but the rotations are isotropic in the liquid, even
at supercooled conditions.Comment: Chemical Physics Letter (in press). 14 pages, 7 figure
New Features of the Morphotropic Phase Boundary in the PbZr(1-x)TixO3 System
Recently a new monoclinic phase in the PbZr(1-x)TixO3 ceramic system has been
reported by Noheda et al. for the composition x= 0.48. In the present work,
samples with Ti contents of x= 0.47 and 0.50, which are both tetragonal below
their Curie points, have been investigated. In the sample with x= 0.50, the
tetragonal phase was found to transform to a monoclinic phase at about 200 K as
the temperature was lowered. The sample with x= 0.47 showed a complicated
region of phase coexistence between 440-320 K, becoming rhombohedral at around
300 K. No further symmetry change was found down to 20 K. Dielectric
measurements for these two samples are also reported. On the basis of these
results, a preliminary phase diagram is presented. Optimum compositional
homogeneity is needed to properly characterize the new monoclinic region.Comment: 5 pages, 7 PS figures embedded. RevTeX and epsf macros. Presented at
the 9th. European Meeting on Ferroelectricity, Prague, July 1999. To be
published in "Ferroelectrics
General study of superscaling in quasielastic and reactions using the relativistic impulse approximation
The phenomenon of superscaling for quasielastic lepton induced reactions at
energies of a few GeV is investigated within the framework of the relativistic
impulse approximation. A global analysis of quasielastic inclusive electron and
charged-current neutrino scattering reactions on nuclei is presented. Scaling
and superscaling properties are shown to emerge from both types of processes.
The crucial role played by final state interactions is evaluated by using
different approaches. The asymmetric shape presented by the experimental
scaling function, with a long tail in the region of positive values of the
scaling variable, is reproduced when the interaction in the final state between
the knockout nucleon and the residual nucleus is described within the
relativistic mean field approach. The impact of gauge ambiguities and off-shell
effects in the scaling function is also analyzed.Comment: 34 pages, 14 figures, accepted in Phys. Rev. C. Section II has been
shortene
Quasielastic Charged Current Neutrino-nucleus Scattering
We provide integrated cross sections for quasielastic charged-current
neutrino-nucleus scattering. Results evaluated using the phenomenological
scaling function extracted from the analysis of experimental data are
compared with those obtained within the framework of the relativistic impulse
approximation. We show that very reasonable agreement is reached when a
description of final-state interactions based on the relativistic mean field is
included. This is consistent with previous studies of differential cross
sections which are in accord with the universality property of the superscaling
function.Comment: 5 pages, 3 figures, to be published in Phys. Rev. Let
Integrated Sachs-Wolfe map recovery from NVSS and WMAP 7yr data
We present a map of the Cosmic Microwave Background (CMB) anisotropies
induced by the late Integrated Sachs Wolfe effect. The map is constructed by
combining the information of the WMAP 7-yr CMB data and the NRAO VLA Sky Survey
(NVSS) through a linear filter. This combination improves the quality of the
map that would be obtained using information only from the Large Scale
Structure data. In order to apply the filter, a given cosmological model needs
to be assumed. In particular, we consider the standard LCDM model. As a test of
consistency, we show that the reconstructed map is in agreemet with the assumed
model, which is also favoured against a scenario where no correlation between
the CMB and NVSS catalogue is considered.Comment: 6 pages, 4 figures. Minor revision, accepted for publication in MNRA
Relativistic descriptions of final-state interactions in charged-current quasielastic neutrino-nucleus scattering at MiniBooNE kinematics
The results of two relativistic models with different descriptions of the
final-state interactions are compared with the MiniBooNE data of
charged-current quasielastic cross sections. The relativistic mean field model
uses the same potential for the bound and ejected nucleon wave functions. In
the relativistic Green's function (RGF) model the final-state interactions are
described in the inclusive scattering consistently with the exclusive
scattering using the same complex optical potential. The RGF results describe
the experimental data for total cross-sections without the need to modify the
nucleon axial mass.Comment: 5 pages 3 figure
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