4,648 research outputs found
Parity Violation and the Nucleon-Nucleon System
The status of the field of nuclear parity violation---both experimental and
theoretical---is reviewed, with special emphasis on those results which have
been obtained since the 1985 review article by Adelberger and Haxton.Comment: 52 page standard Latex file, contribution to the volume "Symmetries
in Nuclear Physics," ed. W.C. Haxton and E. Henle
POLOCALC: a Novel Method to Measure the Absolute Polarization Orientation of the Cosmic Microwave Background
We describe a novel method to measure the absolute orientation of the
polarization plane of the CMB with arcsecond accuracy, enabling unprecedented
measurements for cosmology and fundamental physics. Existing and planned CMB
polarization instruments looking for primordial B-mode signals need an
independent, experimental method for systematics control on the absolute
polarization orientation. The lack of such a method limits the accuracy of the
detection of inflationary gravitational waves, the constraining power on the
neutrino sector through measurements of gravitational lensing of the CMB, the
possibility of detecting Cosmic Birefringence, and the ability to measure
primordial magnetic fields. Sky signals used for calibration and direct
measurements of the detector orientation cannot provide an accuracy better than
1 deg. Self-calibration methods provide better accuracy, but may be affected by
foreground signals and rely heavily on model assumptions. The POLarization
Orientation CALibrator for Cosmology, POLOCALC, will dramatically improve
instrumental accuracy by means of an artificial calibration source flying on
balloons and aerial drones. A balloon-borne calibrator will provide far-field
source for larger telescopes, while a drone will be used for tests and smaller
polarimeters. POLOCALC will also allow a unique method to measure the
telescopes' polarized beam. It will use microwave emitters between 40 and 150
GHz coupled to precise polarizing filters. The orientation of the source
polarization plane will be registered to sky coordinates by star cameras and
gyroscopes with arcsecond accuracy. This project can become a rung in the
calibration ladder for the field: any existing or future CMB polarization
experiment observing our polarization calibrator will enable measurements of
the polarization angle for each detector with respect to absolute sky
coordinates.Comment: 15 pages, 5 figures, Accepted by Journal of Astronomical
Instrumentatio
The binned bispectrum estimator: template-based and non-parametric CMB non-Gaussianity searches
We describe the details of the binned bispectrum estimator as used for the
official 2013 and 2015 analyses of the temperature and polarization CMB maps
from the ESA Planck satellite. The defining aspect of this estimator is the
determination of a map bispectrum (3-point correlator) that has been binned in
harmonic space. For a parametric determination of the non-Gaussianity in the
map (the so-called fNL parameters), one takes the inner product of this binned
bispectrum with theoretically motivated templates. However, as a complementary
approach one can also smooth the binned bispectrum using a variable smoothing
scale in order to suppress noise and make coherent features stand out above the
noise. This allows one to look in a model-independent way for any statistically
significant bispectral signal. This approach is useful for characterizing the
bispectral shape of the galactic foreground emission, for which a theoretical
prediction of the bispectral anisotropy is lacking, and for detecting a
serendipitous primordial signal, for which a theoretical template has not yet
been put forth. Both the template-based and the non-parametric approaches are
described in this paper.Comment: Latex 42 pages with 10 figures and JCAP macros. v2: corrected small
mistake in section 5.3, changed colour scale of slice figures, other minor
changes and additions, matches published versio
Optimally coherent sets in geophysical flows: A new approach to delimiting the stratospheric polar vortex
The "edge" of the Antarctic polar vortex is known to behave as a barrier to
the meridional (poleward) transport of ozone during the austral winter. This
chemical isolation of the polar vortex from the middle and low latitudes
produces an ozone minimum in the vortex region, intensifying the ozone hole
relative to that which would be produced by photochemical processes alone.
Observational determination of the vortex edge remains an active field of
research. In this letter, we obtain objective estimates of the structure of the
polar vortex by introducing a new technique based on transfer operators that
aims to find regions with minimal external transport. Applying this new
technique to European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-40
three-dimensional velocity data we produce an improved three-dimensional
estimate of the vortex location in the upper stratosphere where the vortex is
most pronounced. This novel computational approach has wide potential
application in detecting and analysing mixing structures in a variety of
atmospheric, oceanographic, and general fluid dynamical settings
Performance of a CsI(Tl) calorimeter in an experiment with stopped K+'s
The performance of the photon detector constructed for the search of
T-violation in the decay K^+ -> pi^0 mu^+ nu is presented. The specific
features of this detector consisting of 768 CsI(Tl) crystals with PIN
photodiode readout for high precision measurement of T-odd correlations in the
decays of positive kaons are considered.Comment: 11 pages, 10 figures, talk at the INSTR02 Conference, Novosibirsk,
Russia, February 28 - March 6, 200
Primordial B-mode Diagnostics and Self Calibrating the CMB Polarization
Distortions in the primordial cosmic microwave background (CMB) along the
line-of-sight can be modeled and described using 11 fields. These distortion
fields correspond to various cosmological signals such as weak gravitational
lensing of the CMB by large-scale structure, screening from patchy
reionization, rotation of the plane of polarization due to magnetic fields or
parity violating physics. Various instrumental systematics such as gain
fluctuations, pixel rotation, differential gain, pointing, differential
ellipticity are also described by the same distortion model. All these
distortions produce B-mode that contaminate the primordial tensor B-modes
signal. In this paper we show that apart from generating B-modes, each
distortion uniquely couples different modes (\bfl_1\ne \bfl_2) of the CMB
anisotropies, generating correlations which for the primordial CMB are
zero. We describe and implement unbiased minimum variance quadratic estimators
which using the off diagonal correlations in the CMB can extract the map of
distortions. We perform Monte-Carlo simulations to characterize the estimators
and illustrate the level of distortions that can be detected with current and
future experiments. The estimators can be used to look for cosmological
signals, or to check for any residual systematics in the data. As a specific
example of primordial tensor B-mode diagnostics we compare the level of minimum
detectable distortions using our method with maximum allowed distortion level
for the B-modes detection. We show that for any experiment, the distortions
will be detected at high significance using correlations before they would show
up as spurious B-modes in the power spectrum.Comment: 14 pages, 4 figure
Director Field Model of the Primary Visual Cortex for Contour Detection
We aim to build the simplest possible model capable of detecting long, noisy
contours in a cluttered visual scene. For this, we model the neural dynamics in
the primate primary visual cortex in terms of a continuous director field that
describes the average rate and the average orientational preference of active
neurons at a particular point in the cortex. We then use a linear-nonlinear
dynamical model with long range connectivity patterns to enforce long-range
statistical context present in the analyzed images. The resulting model has
substantially fewer degrees of freedom than traditional models, and yet it can
distinguish large contiguous objects from the background clutter by suppressing
the clutter and by filling-in occluded elements of object contours. This
results in high-precision, high-recall detection of large objects in cluttered
scenes. Parenthetically, our model has a direct correspondence with the Landau
- de Gennes theory of nematic liquid crystal in two dimensions.Comment: 9 pages, 7 figure
Launch of the Space experiment PAMELA
PAMELA is a satellite borne experiment designed to study with great accuracy
cosmic rays of galactic, solar, and trapped nature in a wide energy range
protons: 80 MeV-700 GeV, electrons 50 MeV-400 GeV). Main objective is the study
of the antimatter component: antiprotons (80 MeV-190 GeV), positrons (50
MeV-270 GeV) and search for antimatter with a precision of the order of 10^-8).
The experiment, housed on board the Russian Resurs-DK1 satellite, was launched
on June, 15, 2006 in a 350*600 km orbit with an inclination of 70 degrees. The
detector is composed of a series of scintillator counters arranged at the
extremities of a permanent magnet spectrometer to provide charge,
Time-of-Flight and rigidity information. Lepton/hadron identification is
performed by a Silicon-Tungsten calorimeter and a Neutron detector placed at
the bottom of the device. An Anticounter system is used offline to reject false
triggers coming from the satellite. In self-trigger mode the Calorimeter, the
neutron detector and a shower tail catcher are capable of an independent
measure of the lepton component up to 2 TeV. In this work we describe the
experiment, its scientific objectives and the performance in the first months
after launch.Comment: Accepted for publication on Advances in Space Researc
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