1,653 research outputs found

### Generic description of CMB power spectra

Taking advantage of the smoothness of CMB Cl power spectra, we derive a
simple and model-independent parameterization of their measurement. It allows
to describe completely the spectrum, ie. provide an estimate of the value and
the error for any real l point at the percent level, down to low l multipole.
We provide this parameterization for WMAP first year data and show that the
spectrum is consistent with the smoothness hypothesis. We also show how such a
parameterization allows to retrieve the Cl spectra from the measurement of
Fourier rings on the sky (Gamma(m)) or from the angular correlation function
(c(theta)

### Overall determination of the CKM matrix

We discuss the problem of theoretical uncertainties in the combination of
observables related to the CKM matrix elements and propose a statistically
sensible method for combining them. The overall fit is performed on present
data, and constraints on the matrix elements are presented as well as on
fB*sqrt(Bb). We then explore the implications of recent measurements and
developments: jpsi-KS CP asymmetry, epsilon_prime/epsilon and B -> K pi
branching fractions. Finally, we extract from the overall fit the Standard
Model expectations for the rare kaon decays K -> pi nu anti-nu.Comment: Talk given at Heavy Flavours 8, Southampton, UK, 199

### 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

### A novel estimator of the polarization amplitude from normally distributed Stokes parameters

We propose a novel estimator of the polarization amplitude from a single
measurement of its normally distributed $(Q,U)$ Stokes components. Based on the
properties of the Rice distribution and dubbed 'MAS' (Modified ASymptotic), it
meets several desirable criteria:(i) its values lie in the whole positive
region; (ii) its distribution is continuous; (iii) it transforms smoothly with
the signal-to-noise ratio (SNR) from a Rayleigh-like shape to a Gaussian one;
(iv) it is unbiased and reaches its components' variance as soon as the SNR
exceeds 2; (v) it is analytic and can therefore be used on large data-sets. We
also revisit the construction of its associated confidence intervals and show
how the Feldman-Cousins prescription efficiently solves the issue of classical
intervals lying entirely in the unphysical negative domain. Such intervals can
be used to identify statistically significant polarized regions and conversely
build masks for polarization data. We then consider the case of a general
$[Q,U]$ covariance matrix and perform a generalization of the estimator that
preserves its asymptotic properties. We show that its bias does not depend on
the true polarization angle, and provide an analytic estimate of its variance.
The estimator value, together with its variance, provide a powerful
point-estimate of the true polarization amplitude that follows an unbiased
Gaussian distribution for a SNR as low as 2. These results can be applied to
the much more general case of transforming any normally distributed random
variable from Cartesian to polar coordinates.Comment: Accepted by MNRA

### CP violation with BaBar

The BABAR experiment is a new generation detector located at the SLAC B
factory PEP-II ring which should start taking data at the end of 1999. Its main
goal is the study of CP violation in the B0-B0b system. After explaining the
nature of this CP violation, I review the scientific program for achieving this
study in many different modes, in the light of the recent developments obtained
both on the experimental and theoretical side. Implications for the Standard
Model are then discussed.Comment: 17 pages, 8 postscript figures (using epsfig.sty

### Agnostic cosmology in the CAMEL framework

Cosmological parameter estimation is traditionally performed in the Bayesian
context. By adopting an "agnostic" statistical point of view, we show the
interest of confronting the Bayesian results to a frequentist approach based on
profile-likelihoods. To this purpose, we have developed the Cosmological
Analysis with a Minuit Exploration of the Likelihood ("CAMEL") software.
Written from scratch in pure C++, emphasis was put in building a clean and
carefully-designed project where new data and/or cosmological computations can
be easily included.
CAMEL incorporates the latest cosmological likelihoods and gives access from
the very same input file to several estimation methods: (i) A high quality
Maximum Likelihood Estimate (a.k.a "best fit") using MINUIT ; (ii) profile
likelihoods, (iii) a new implementation of an Adaptive Metropolis MCMC
algorithm that relieves the burden of reconstructing the proposal distribution.
We present here those various statistical techniques and roll out a full
use-case that can then used as a tutorial. We revisit the $\Lambda$CDM
parameters determination with the latest Planck data and give results with both
methodologies. Furthermore, by comparing the Bayesian and frequentist
approaches, we discuss a "likelihood volume effect" that affects the optical
reionization depth when analyzing the high multipoles part of the Planck data.
The software, used in several Planck data analyzes, is available from
http://camel.in2p3.fr. Using it does not require advanced C++ skills.Comment: Typeset in Authorea. Online version available at:
https://www.authorea.com/users/90225/articles/104431/_show_articl

### Reconstruction of the cosmic microwave background lensing for Planck

Aims. We prepare real-life cosmic microwave background (CMB) lensing extraction with the forthcoming Planck satellite data by studying two systematic effects related to the foreground contamination: the impact of foreground residuals after a component separation on the lensed CMB map, and the impact of removing a large contaminated region of the sky.
Methods. We first use the generalized morphological component analysis (GMCA) method to perform a component separation within a simplified framework, which allows a high statistics Monte-Carlo study. For the second systematic, we apply a realistic mask on the temperature maps and then restore them with a recently developed inpainting technique on the sphere. We investigate the reconstruction of the CMB lensing from the resultant maps using a quadratic estimator in the flat sky limit and on the full sphere.
Results. We find that the foreground residuals from the GMCA method does not significantly alter the lensed signal, which is also true for the mask corrected with the inpainting method, even in the presence of point source residuals

### Relieving tensions related to the lensing of CMB temperature power spectra

The angular power spectra of the cosmic microwave background (CMB)
temperature anisotropies reconstructed from Planck data seem to present too
much gravitational lensing distortion. This is quantified by the control
parameter $A_L$ that should be compatible with unity for a standard cosmology.
With the Class Boltzmann solver and the profile-likelihood method, for this
parameter we measure a 2.6$\sigma$ shift from 1 using the Planck public
likelihoods. We show that, owing to strong correlations with the reionization
optical depth $\tau$ and the primordial perturbation amplitude $A_s$, a
$\sim2\sigma$ tension on $\tau$ also appears between the results obtained with
the low ($\ell\leq 30$) and high ($30<\ell\lesssim 2500$) multipoles
likelihoods. With Hillipop, another high-$\ell$ likelihood built from Planck
data, this difference is lowered to $1.3\sigma$. In this case, the $A_L$ value
is still in disagreement with unity by $2.2\sigma$, suggesting a non-trivial
effect of the correlations between cosmological and nuisance parameters. To
better constrain the nuisance foregrounds parameters, we include the very high
$\ell$ measurements of the Atacama Cosmology Telescope (ACT) and South Pole
Telescope (SPT) experiments and obtain $A_L = 1.03 \pm 0.08$. The
Hillipop+ACT+SPT likelihood estimate of the optical depth is
$\tau=0.052\pm{0.035,}$ which is now fully compatible with the low $\ell$
likelihood determination. After showing the robustness of our results with
various combinations, we investigate the reasons for this improvement that
results from a better determination of the whole set of foregrounds parameters.
We finally provide estimates of the $\Lambda$CDM parameters with our combined
CMB data likelihood.Comment: accepted by A&

- âŠ