947 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)
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 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
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
Neutrino matter with PLANCK
After reviewing the main mechanisms by which cosmological measurements
constrain the sum of neutrino masses, I give the current reached upper limits,
emphasizing the level of model-dependence. A large improvement is to be
expected with PLANCK's satellite data, on which I give some news, in particular
due to the characterization of the CMB-lensing effect. It will however require
a thorough control of many systematics effects upon which progress has been
made recently.Comment: Invited Talk at Identification of Dark Matter 2010-IDM2010, July
26-30, 2010, Montpellier France. This paper has been temporarily withdrawn
until it receives approval from the Planck Editorial Boar
DIRC for a Higher Luminosity B Factory
The DIRC, a novel type of Cherenkov ring imaging device, is the primary
hadronic particle identification system for the BaBar detector at the
asymmetric B-factory Pep-II at SLAC. It is based on total internal reflection
and uses long, rectangular bars made from synthetic fused silica as Cherenkov
radiators and light guides. BaBar began taking data with colliding beams in
late spring 1999. This paper describes the challenges for the DIRC in a higher
luminosity environment and shows solutions to these challenges.Comment: 16 page
A hybrid approach to CMB lensing reconstruction on all-sky intensity maps
Based on realistic simulations, we propose an hybrid method to reconstruct
the lensing potential power spectrum, directly on PLANCK-like CMB frequency
maps. It implies using a large galactic mask and dealing with a strong
inhomogeneous noise. For l < 100, we show that a full-sky inpainting method,
already described in a previous work, still allows a minimal variance
reconstruction, with a bias that must be accounted for by a Monte-Carlo method,
but that does not couple to the deflection field. For l>100 we develop a method
based on tiling the cut-sky with local 10x10 degrees overlapping tangent planes
(referred to in the following as "patches"). It requires to solve various
issues concerning their size/position, non-periodic boundaries and irregularly
sampled data after the sphere-to-plane projection. We show how the leading
noise term of the quadratic lensing estimator applied onto an apodized patch
can still be taken directly from the data. To not loose spatial accuracy, we
developed a tool that allows the fast determination of the complex Fourier
series coefficients from a bi-dimensional irregularly sampled dataset, without
performing an interpolation. We show that the multi-patch approach allows the
lensing power spectrum reconstruction with a very small bias, thanks to
avoiding the galactic mask and lowering the noise inhomogeneities, while still
having almost a minimal variance. The data quality can be assessed at each
stage and simple bi-dimensional spectra build, which allows the control of
local systematic errors.Comment: A&A version. Mostly english correction
Impact of Bottom-Quark Measurements on our Knowledge of the Standard Model
In this decade, B-decay experiments will allow stringent tests of the
Standard-Model description of CP violation. After a classification of the main
strategies and a discussion of the most recent results on benchmark decay modes
of and mesons, we focus on the "El Dorado" for hadron colliders,
the -meson system, discussing the differences between the and
systems, as well as prominent modes. First access to these decays is
already provided by run II of the Tevatron. In the LHC era, it will be possible
to fully exploit their physics potential, in particular at LHCb and BTeV.Comment: 19 pages, 4 figures. Invited talk at the 14th Topical Conference on
Hadron Collider Physics, Karlsruhe, Germany, 29 September - 4 October 2002.
To appear in the Proceeding
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