110 research outputs found
A close examination of cosmic microwave background mirror-parity after Planck
Previous claims of significant evidence for mirror-parity in the large-scale
cosmic microwave background (CMB) data from the Wilkinson Microwave Anisotropy
Probe (WMAP) experiment have been recently echoed in the first study of
isotropy and statistics of CMB data from Planck. We revisit these claims with a
careful analysis of the latest data available. We construct statistical
estimators in both harmonic and pixel space, test them on simulated data with
and without mirror-parity symmetry, apply different Galactic masks, and study
the dependence of the results on arbitrary choices of free parameters. We
confirm that the data exhibit evidence for odd mirror-parity at a significance
which reaches as high as ~ 99 per cent C.L., under some circumstances. However,
given the inherent biases in the pixel-based statistic and the dependence of
both pixel and harmonic space statistics on the particular form of Galactic
masking and other a-posteriori choices, we conclude that these results are not
in significant tension with the predictions of the concordance cosmological
model.Comment: 9 pages, 5 figures, minor changes, as published in MNRA
The Kullback-Leibler Divergence as an Estimator of the Statistical Properties of CMB Maps
The identification of unsubtracted foreground residuals in the cosmic
microwave background maps on large scales is of crucial importance for the
analysis of polarization signals. These residuals add a non-Gaussian
contribution to the data. We propose the Kullback-Leibler (KL) divergence as an
effective, non-parametric test on the one-point probability distribution
function of the data. With motivation in information theory, the KL divergence
takes into account the entire range of the distribution and is highly
non-local. We demonstrate its use by analyzing the large scales of the Planck
2013 SMICA temperature fluctuation map and find it consistent with the expected
distribution at a level of 6%. Comparing the results to those obtained using
the more popular Kolmogorov-Smirnov test, we find the two methods to be in
general agreement.Comment: 12 pages, 5 figures, minor change, as published in JCA
Skewness and Kurtosis as Indicators of Non-Gaussianity in Galactic Foreground Maps
Observational cosmology is entering an era in which high precision will be
required in both measurement and data analysis. Accuracy, however, can only be
achieved with a thorough understanding of potential sources of contamination
from foreground effects. Our primary focus will be on non- Gaussian effects in
foregrounds. This issue will be crucial for coming experiments to determine
B-mode polarization. We propose a novel method for investigating a data set in
terms of skewness and kurtosis in locally defined regions that collectively
cover the entire sky. The method is demonstrated on two sky maps: (i) the SMICA
map of Cosmic Microwave Background fluctuations provided by the Planck
Collaboration and (ii) a version of the Haslam map at 408 MHz that describes
synchrotron radiation. We find that skewness and kurtosis can be evaluated in
combination to reveal local physical information. In the present case, we
demonstrate that the local properties of both maps are predominantly Gaussian.
This result was expected for the SMICA map; that it also applies for the Haslam
map is surprising. The approach described here has a generality and flexibility
that should make it useful in a variety of astrophysical and cosmological
contexts.Comment: 15 pages, 7 figures, minor change, as published in JCA
Parity in the CMB: Space Oddity
We search for a direction in the sky that exhibits parity symmetry under
reflections through a plane. We use the natural estimator, which compares the
power in even and odd multipoles, and apply minimal blind masking of
outliers to the ILC map in order to avoid large errors in the reconstruction of
multipoles. The multipoles of the cut sky are calculated both naively and by
using the covariance inversion method and we estimate the significance of our
results using CDM simulations. Focusing on low multipoles, with or even 7, we find two perpendicular
directions of even and odd parity in the map. While the even parity direction
does not appear significant, the odd direction is quite significant -- at least
a effect.Comment: 6 pages, 7 figures. Accepted for publication in The Astrophysical
Journa
Understanding the Scope of Business Law Clinics: Perspectives from the United Kingdom, Israel and the United States
The impetus for the emergence of business law clinics across jurisdictions is remarkably similar: commercially orientated education and development of students combined with a reconceptualised social justice agenda which embraces entrepreneurial activity in all forms. Business law clinics face the challenge of balancing the interests of students and clients,of service provision versus learning environment, within a distinctly entrepreneurial environment. To achieve this, we must enter into a dialogue and embrace a common mission. This article addresses the gap in the literature with a comparative analysis of the Business and Commercial Law Clinic at Northumbria Law School, England; The Interdisciplinary Center Herzliya Legal Clinic for Start-Ups at Radzyner Law School, Israel; and BrooklynLaw Incubator & Policy Clinic at Brooklyn Law School, United States. We posit that business law clinics should be valued for their rich educational experience, the important assistance they provide and the wider benefits they bestow on teaching institutions
Giant Rings in the CMB Sky
We find a unique direction in the CMB sky around which giant rings have an
anomalous mean temperature profile. This direction is in very close alignment
with the afore measured anomalously large bulk flow direction. Using Monte
Carlo simulations, we estimate the significance of the giant rings at the
level and the alignment with the bulk flow at . We argue
that a cosmic defect seeded by a pre-inflationary particle could explain the
giant rings, the large bulk flow and their alignment.Comment: 6 pages, 7 figures, accepted for publication in The Astrophysical
Journa
Experimental Study of Parametric Autoresonance in Faraday Waves
The excitation of large amplitude nonlinear waves is achieved via parametric
autoresonance of Faraday waves. We experimentally demonstrate that phase
locking to low amplitude driving can generate persistent high-amplitude growth
of nonlinear waves in a dissipative system. The experiments presented are in
excellent agreement with theory.Comment: 4 pages, 4 eps figures, to appear in Phys. Rev. Let
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