211 research outputs found
Constraints on neutrino and dark radiation interactions using cosmological observations
Observations of the cosmic microwave background (CMB) and large-scale
structure (LSS) provide a unique opportunity to explore the fundamental
properties of the constituents that compose the cosmic dark radiation
background (CDRB), of which the three standard neutrinos are thought to be the
dominant component. We report on the first constraint to the CDRB rest-frame
sound speed, ceff^2, using the most recent CMB and LSS data. Additionally, we
report improved constraints to the CDRB viscosity parameter, cvis^2. For a
non-interacting species, these parameters both equal 1/3. Using current data we
find that a standard CDRB, composed entirely of three non-interacting neutrino
species, is ruled out at the 99% confidence level (C.L.) with ceff^2 = 0.30
+0.027 -0.026 and cvis^2 = 0.44 +0.27 -0.21 (95% C.L.). We also discuss how
constraints to these parameters from current and future observations (such as
the Planck satellite) allow us to explore the fundamental properties of any
anomalous radiative energy density beyond the standard three neutrinos.Comment: 6 pages, 3 figures, comments welcome; v2: updated with SPT data,
corrected minor typos; v3: version accepted for publication in PR
CMB Lensing Constraints on Neutrinos and Dark Energy
Signatures of lensing of the cosmic microwave background radiation by
gravitational potentials along the line of sight carry with them information on
the matter distribution, neutrino masses, and dark energy properties. We
examine the constraints that Planck, PolarBear, and CMBpol future data,
including from the B-mode polarization or the lensing potential, will be able
to place on these quantities. We simultaneously fit for neutrino mass and dark
energy equation of state including time variation and early dark energy
density, and compare the use of polarization power spectra with an optimal
quadratic estimator of the lensing. Results are given as a function of
systematics level from residual foreground contamination. A realistic CMBpol
experiment can effectively constrain the sum of neutrino masses to within 0.05
eV and the fraction of early dark energy to 0.002. We also present a
surprisingly simple prescription for calculating dark energy equation of state
constraints in combination with supernova distances from JDEM.Comment: 18 pages, 14 figures. Small changes made to match version to be
published in Phys. Rev.
Reconstruction of Gravitational Lensing Using WMAP 7-Year Data
Gravitational lensing by large scale structure introduces non-Gaussianity
into the Cosmic Microwave Background and imprints a new observable, which can
be used as a cosmological probe. We apply a four-point estimator to the
Wilkinson Microwave Anisotropy Probe (WMAP) 7-year coadded temperature maps
alone to reconstruct the gravitational lensing signal. The Gaussian bias is
simulated and subtracted, and the higher order bias is investigated. We measure
a gravitational lensing signal with a statistical amplitude of =
using all the correlations of the W- and V-band Differencing
Assemblies (DAs). We therefore conclude that WMAP 7-year data alone, can not
detect lensing.Comment: 10 pages, 10 figure
From Cavendish to PLANCK: Constraining Newton's Gravitational Constant with CMB Temperature and Polarization Anisotropy
We present new constraints on cosmic variations of Newton's gravitational
constant by making use of the latest CMB data from WMAP, BOOMERANG, CBI and
ACBAR experiments and independent constraints coming from Big Bang
Nucleosynthesis. We found that current CMB data provide constraints at the 10%
level, that can be improved to 3% by including BBN data. We show that future
data expected from the Planck satellite could constrain G at the 1.5% level
while an ultimate, cosmic variance limited, CMB experiment could reach a
precision of about 0.4%, competitive with current laboratory measurements.Comment: 6 pages, 8 figures, corrected typos, added reference
Probing the Friedmann equation during recombination with future CMB experiments
We show that by combining measurements of the temperature and polarization
anisotropies of the Cosmic Microwave Background (CMB), future experiments will
tightly constrain the expansion rate of the universe during recombination. A
change in the expansion rate modifies the way in which the recombination of
hydrogen proceeds, altering the shape of the acoustic peaks and the level of
CMB polarization. The proposed test is similar in spirit to the examination of
abundances of light elements produced during Big Bang Nucleosynthesis and it
constitutes a way to study possible departures from standard recombination. For
simplicity we parametrize the change in the Friedmann equation by changing the
gravitational constant . The main effect on the temperature power spectrum
is a change in the degree of damping of the acoustic peaks on small angular
scales. The effect can be compensated by a change in the shape of the
primordial power spectrum. We show that this degeneracy between the expansion
rate and the primordial spectrum can be broken by measuring CMB polarization.
In particular we show that the MAP satellite could obtain a constraint for the
expansion rate during recombination of or after observing for four years, whereas Planck could obtain
or within two years, even after
allowing for further freedom in the shape of the power spectrum of primordial
fluctuations.Comment: Replaced to match published PRD version. ACBAR and new Boomerang data
included in analysis. References added. 13 pages, 11 figure
The morphology of HII regions during reionization
It is possible that the properties of HII regions during reionization depend
sensitively on many poorly constrained quantities (the nature of the ionizing
sources, the clumpiness of the gas in the IGM, the degree to which
photo-ionizing feedback suppresses the abundance of low mass galaxies, etc.),
making it extremely difficult to interpret upcoming observations of this epoch.
We demonstrate that the actual situation is more encouraging, using a suite of
radiative transfer simulations, post-processed on outputs from a 1024^3, 94 Mpc
N-body simulation. Analytic prescriptions are used to incorporate small-scale
structures that affect reionization, yet remain unresolved in the N-body
simulation. We show that the morphology of the HII regions is most dependent on
the global ionization fraction x_i. This is not to say that the bubble
morphology is completely independent of all parameters besides x_i. The next
most important dependence is that of the nature of the ionizing sources. The
rarer the sources, the larger and more spherical the HII regions become. The
typical bubble size can vary by as much as a factor of 4 at fixed x_i between
different possible source prescriptions. The final relevant factor is the
abundance of minihalos or of Lyman-limit systems. These systems suppress the
largest bubbles from growing, and the magnitude of this suppression depends on
the thermal history of the gas as well as the rate at which minihalos are
photo-evaporated. We find that neither source suppression owing to
photo-heating nor gas clumping significantly affect the large-scale structure
of the HII regions. We discuss how observations of the 21cm line with MWA and
LOFAR can constrain properties of reionization, and we study the effect patchy
reionization has on the statistics of Lyman-alpha emitting galaxies. [abridged]Comment: 23 pages, 18 figure
Delensing CMB Polarization with External Datasets
One of the primary scientific targets of current and future CMB polarization
experiments is the search for a stochastic background of gravity waves in the
early universe. As instrumental sensitivity improves, the limiting factor will
eventually be B-mode power generated by gravitational lensing, which can be
removed through use of so-called delensing algorithms. We forecast prospects
for delensing using lensing maps which are obtained externally to CMB
polarization: either from large-scale structure observations, or from
high-resolution maps of CMB temperature. We conclude that the forecasts in
either case are not encouraging, and that significantly delensing large-scale
CMB polarization requires high-resolution polarization maps with sufficient
sensitivity to measure the lensing B-mode. We also present a simple formalism
for including delensing in CMB forecasts which is computationally fast and
agrees well with Monte Carlos.Comment: typos correcte
Illuminating the Universe : New Probes of Reionization and Cosmology
We model the epoch of hydrogen reionisation of the universe, using analytic as well as numerical methods. In a detailed statistical analysis of our results, we find good agreement in the alternative descriptions of the morphology of ionized regions. We use the simulations to make predictions for reionisation observables that should be accessible within a few years years: the kinetic Sunyaev-Zel'dovich effect and fluctuations in the 21 cm spin flip transition of neutral hydrogen. We also propose to use the 21 cm signal to constrain cosmological parameters by probing the matter power spectrum. We also make use of the observable as s source screen for gravitational lensing by large scale structure, and develop a formalism to extract the lens distribution from the characteristics of the lensed 21 cm field
Locating disparities in machine learning
Machine learning can provide predictions with disparate outcomes, in which
subgroups of the population (e.g., defined by age, gender, or other sensitive
attributes) are systematically disadvantaged. In order to comply with upcoming
legislation, practitioners need to locate such disparate outcomes. However,
previous literature typically detects disparities through statistical
procedures for when the sensitive attribute is specified a priori. This limits
applicability in real-world settings where datasets are high dimensional and,
on top of that, sensitive attributes may be unknown. As a remedy, we propose a
data-driven framework called Automatic Location of Disparities (ALD) which aims
at locating disparities in machine learning. ALD meets several demands from
industry: ALD (1) is applicable to arbitrary machine learning classifiers; (2)
operates on different definitions of disparities (e.g., statistical parity or
equalized odds); and (3) deals with both categorical and continuous predictors
even if disparities arise from complex and multi-way interactions known as
intersectionality (e. g., age above 60 and female). ALD produces interpretable
audit reports as output. We demonstrate the effectiveness of ALD based on both
synthetic and real-world datasets. As a result, we empower practitioners to
effectively locate and mitigate disparities in machine learning algorithms,
conduct algorithmic audits, and protect individuals from discrimination
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