2,818 research outputs found
Is there evidence for additional neutrino species from cosmology?
It has been suggested that recent cosmological and flavor-oscillation data
favor the existence of additional neutrino species beyond the three predicted
by the Standard Model of particle physics. We apply Bayesian model selection to
determine whether there is indeed any evidence from current cosmological
datasets for the standard cosmological model to be extended to include
additional neutrino flavors. The datasets employed include cosmic microwave
background temperature, polarization and lensing power spectra, and
measurements of the baryon acoustic oscillation scale and the Hubble constant.
We also consider other extensions to the standard neutrino model, such as
massive neutrinos, and possible degeneracies with other cosmological
parameters. The Bayesian evidence indicates that current cosmological data do
not require any non-standard neutrino properties.Comment: 17 pages, 7 figures. v3: replaced with version published in JCAP
(typo fixes, including Figure 1 units
Avoiding bias in reconstructing the largest observable scales from partial-sky data
Obscuration due to Galactic emission complicates the extraction of
information from cosmological surveys, and requires some combination of the
(typically imperfect) modeling and subtraction of foregrounds, or the removal
of part of the sky. This particularly affects the extraction of information
from the largest observable scales. Maximum-likelihood estimators for
reconstructing the full-sky spherical harmonic coefficients from partial-sky
maps have recently been shown to be susceptible to contamination from within
the sky cut, arising due to the necessity to band-limit the data by smoothing
prior to reconstruction. Using the WMAP 7-year data, we investigate modified
implementations of such estimators which are robust to the leakage of
contaminants from within masked regions. We provide a measure, based on the
expected amplitude of residual foregrounds, for selecting the most appropriate
estimator for the task at hand. We explain why the related quadratic
maximum-likelihood estimator of the angular power spectrum does not suffer from
smoothing-induced bias.Comment: 8 pages, 8 figures. v2: replaced with version accepted by PRD (minor
amendments to text only
Robust forecasts on fundamental physics from the foreground-obscured, gravitationally-lensed CMB polarization
[Abridged] Recent results from the BICEP, Keck Array and Planck
Collaborations demonstrate that Galactic foregrounds are an unavoidable
obstacle in the search for evidence of inflationary gravitational waves in the
cosmic microwave background (CMB) polarization. Beyond the foregrounds, the
effect of lensing by intervening large-scale structure further obscures all but
the strongest inflationary signals permitted by current data. With a plethora
of ongoing and upcoming experiments aiming to measure these signatures, careful
and self-consistent consideration of experiments' foreground- and
lensing-removal capabilities is critical in obtaining credible forecasts of
their performance. We investigate the capabilities of instruments such as
Advanced ACTPol, BICEP3 and Keck Array, CLASS, EBEX10K, PIPER, Simons Array,
SPT-3G and SPIDER, and projects as COrE+, LiteBIRD-ext, PIXIE and Stage IV, to
clean contamination due to polarized synchrotron and dust from raw
multi-frequency data, and remove lensing from the resulting co-added CMB maps
(either using iterative CMB-only techniques or through cross-correlation with
external data). Incorporating these effects, we present forecasts for the
constraining power of these experiments in terms of inflationary physics, the
neutrino sector, and dark energy parameters. Made publicly available through an
online interface, this tool enables the next generation of CMB experiments to
foreground-proof their designs, optimize their frequency coverage to maximize
scientific output, and determine where cross-experimental collaboration would
be most beneficial. We find that analyzing data from ground, balloon and space
instruments in complementary combinations can significantly improve component
separation performance, delensing, and cosmological constraints over individual
datasets.Comment: 37 pages plus appendices, 15 figures; first two authors contributed
equally to this work; forecasting tool available at http://turkey.lbl.gov.
v4: matches version published in JCAP (with extended dark energy constraints
Forecasting constraints from the cosmic microwave background on eternal inflation
We forecast the ability of cosmic microwave background (CMB) temperature and
polarization datasets to constrain theories of eternal inflation using cosmic
bubble collisions. Using the Fisher matrix formalism, we determine both the
overall detectability of bubble collisions and the constraints achievable on
the fundamental parameters describing the underlying theory. The CMB signatures
considered are based on state-of-the-art numerical relativistic simulations of
the bubble collision spacetime, evolved using the full temperature and
polarization transfer functions. Comparing a theoretical
cosmic-variance-limited experiment to the WMAP and Planck satellites, we find
that there is no improvement to be gained from future temperature data, that
adding polarization improves detectability by approximately 30%, and that
cosmic-variance-limited polarization data offer only marginal improvements over
Planck. The fundamental parameter constraints achievable depend on the precise
values of the tensor-to-scalar ratio and energy density in (negative) spatial
curvature. For a tensor-to-scalar ratio of and spatial curvature at the
level of , using cosmic-variance-limited data it is possible to
measure the width of the potential barrier separating the inflating false
vacuum from the true vacuum down to , and the initial proper
distance between colliding bubbles to a factor of the false vacuum
horizon size (at three sigma). We conclude that very near-future data will have
the final word on bubble collisions in the CMB.Comment: 14 pages, 6 figure
Mucosal neuroimmune mechanisms in gastro-oesophageal reflux disease (GORD) pathogenesis.
Gastro-oesophageal reflux disease (GORD) is a chronic condition characterised by visceral pain in the distal oesophagus. The current first-line treatment for GORD is proton pump inhibitors (PPIs), however, PPIs are ineffective in a large cohort of patients and long-term use may have adverse effects. Emerging evidence suggests that nerve fibre number and location are likely to play interrelated roles in nociception in the oesophagus of GORD patients. Simultaneously, alterations in cells of the oesophageal mucosa, namely epithelial cells, mast cells, dendritic cells, and T lymphocytes, have been a focus of GORD research for several years. The oesophagus of GORD patients exhibits both macro- and micro-inflammation as a response to chronic acidic reflux at the epithelium. In other conditions of the GI tract, such as IBS and IBD, well-characterised bidirectional processes between immune cells and mucosal nerve fibres contribute to pathogenesis and symptom generation. Sensory alterations in these conditions such as nerve fibre outgrowth and hypersensitivity can be driven by inflammatory processes, which promote visceral pain signalling. This review will examine what is currently known of the molecular pathways linking inflammation and sensory perception leading to the development of GORD symptoms and explore potentially relevant mechanisms in other GI regions which may indicate new areas in GORD research
A novel sampling theorem on the rotation group
We develop a novel sampling theorem for functions defined on the
three-dimensional rotation group SO(3) by connecting the rotation group to the
three-torus through a periodic extension. Our sampling theorem requires
samples to capture all of the information content of a signal band-limited at
, reducing the number of required samples by a factor of two compared to
other equiangular sampling theorems. We present fast algorithms to compute the
associated Fourier transform on the rotation group, the so-called Wigner
transform, which scale as , compared to the naive scaling of .
For the common case of a low directional band-limit , complexity is reduced
to . Our fast algorithms will be of direct use in speeding up the
computation of directional wavelet transforms on the sphere. We make our SO3
code implementing these algorithms publicly available.Comment: 5 pages, 2 figures, minor changes to match version accepted for
publication. Code available at http://www.sothree.or
First Observational Tests of Eternal Inflation
The eternal inflation scenario predicts that our observable Universe resides inside a single bubble embedded in a vast inflating multiverse. We present the first observational tests of eternal inflation, performing a search for cosmological signatures of collisions with other bubble universes in cosmic microwave background data from the WMAP satellite. We conclude that the WMAP 7-year data do not warrant augmenting the cold dark matter model with a cosmological constant with bubble collisions, constraining the average number of detectable bubble collisions on the full sky N̅ _s<1.6 at 68% C.L. Data from the Planck satellite can be used to more definitively test the bubble-collision hypothesis
A robust constraint on cosmic textures from the cosmic microwave background
Fluctuations in the cosmic microwave background (CMB) contain information
which has been pivotal in establishing the current cosmological model. These
data can also be used to test well-motivated additions to this model, such as
cosmic textures. Textures are a type of topological defect that can be produced
during a cosmological phase transition in the early universe, and which leave
characteristic hot and cold spots in the CMB. We apply Bayesian methods to
carry out a rigorous test of the texture hypothesis, using full-sky data from
the Wilkinson Microwave Anisotropy Probe. We conclude that current data do not
warrant augmenting the standard cosmological model with textures. We rule out
at 95% confidence models that predict more than 6 detectable cosmic textures on
the full sky.Comment: 5 pages, 2 figures. v2: replaced with version accepted by PRL (minor
amendments to reduce length and address referee comments
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