650 research outputs found
A new life for sterile neutrinos: resolving inconsistencies using hot dark matter
Within the standard LCDM model of cosmology, the recent Planck measurements
have shown discrepancies with other observations, e.g., measurements of the
current expansion rate H_0, the galaxy shear power spectrum and counts of
galaxy clusters. We show that if LCDM is extended by a hot dark matter
component, which could be interpreted as a sterile neutrino, the data sets can
be combined consistently. A combination of Planck data, WMAP-9 polarisation
data, measurements of the BAO scale, the HST measurement of H_0, Planck galaxy
cluster counts and galaxy shear data from the CFHTLens survey yields Delta
N_eff = 0.61 pm 0.30 and m_s^eff = (0.41 pm 0.13) eV at 1 sigma. The former is
driven mainly by the large H_0 of the HST measurement, while the latter is
driven by cluster data. CFHTLens galaxy shear data prefer Delta N_eff >0 and a
non-zero mass. Taken together, we find hints for the presence of a hot dark
matter component at 3 sigma. A sterile neutrino motivated by the reactor and
gallium anomalies appears rejected at even higher significance and an
accelerator anomaly sterile neutrino is found in tension at 2 sigma.Comment: 11 pages, 2 figures; v2: 12 pages, 3 figures, references added and
discussion slightly expanded, matches version published in JCA
How to constrain inflationary parameter space with minimal priors
We update constraints on the Hubble function H(phi) during inflation, using
the most recent cosmic microwave background (CMB) and large scale structure
(LSS) data. Our main focus is on a comparison between various commonly used
methods of calculating the primordial power spectrum via analytical
approximations and the results obtained by integrating the exact equations
numerically. In each case, we impose naive, minimally restrictive priors on the
duration of inflation. We find that the choice of priors has an impact on the
results: the bounds on inflationary parameters can vary by up to a factor two.
Nevertheless, it should be noted that within the region allowed by the minimal
prior of the exact method, the accuracy of the approximations is sufficient for
current data. We caution however that a careless minimal implementation of the
approximative methods allows models for which the assumptions behind the
analytical approximations fail, and recommend using the exact numerical method
for a self-consistent analysis of cosmological data.Comment: 16 pages, 3 figure
Precise measurements of inflationary features with 21 cm observations
Future observations of 21~cm emission using HI intensity mapping will enable
us to probe the large scale structure of the Universe over very large survey
volumes within a reasonable observation time. We demonstrate that the
three-dimensional information contained in such surveys will be an extremely
powerful tool in searching for features that were imprinted in the primordial
power spectrum and bispectrum during inflation. Here we focus on the "resonant"
and "step" inflation models, and forecast the potential of upcoming 21~cm
experiments to detect these inflationary features in the observable power- and
bispectrum. We find that the full scale Tianlai experiment and the Square
Kilometre Array (SKA) have the potential to improve on the sensitivity of
current Cosmic Microwave Background (CMB) experiments by several orders of
magnitude.Comment: 7 pages, 3 figures, replaced with revised versio
Features in the primordial power spectrum? A frequentist analysis
Features in the primordial power spectrum have been suggested as an
explanation for glitches in the angular power spectrum of temperature
anisotropies measured by the WMAP satellite. However, these glitches might just
as well be artifacts of noise or cosmic variance. Using the effective Delta
chi^2 between the best-fit power-law spectrum and a deconvolved primordial
spectrum as a measure of "featureness" of the data, we perform a full
Monte-Carlo analysis to address the question of how significant the recovered
features are. We find that in 26% of the simulated data sets the reconstructed
spectrum yields a greater improvement in the likelihood than for the actually
observed data. While features cannot be categorically ruled out by this
analysis, and the possibility remains that simple theoretical models which
predict some of the observed features might stand up to rigorous statistical
testing, our results suggest that WMAP data are consistent with the assumption
of a featureless power-law primordial spectrum.Comment: 17 pages, 3 figures; v2: minor changes, matches published versio
The Impact of Prior Assumptions on Bayesian Estimates of Inflation Parameters and the Expected Gravitational Waves Signal from Inflation
There has been much recent discussion, and some confusion, regarding the use
of existing observational data to estimate the likelihood that next-generation
cosmic microwave background (CMB) polarization experiments might detect a
nonzero tensor signal, possibly associated with inflation. We examine this
issue in detail here in two different ways: (1) first we explore the effect of
choice of different parameter priors on the estimation of the tensor-to-scalar
ratio r and other parameters describing inflation, and (2) we examine the
Bayesian complexity in order to determine how effectively existing data can
constrain inflationary parameters. We demonstrate that existing data are not
strong enough to render full inflationary parameter estimates in a
parametrization- and prior-independent way and that the predicted tensor signal
is particularly sensitive to different priors. For parametrizations where the
Bayesian complexity is comparable to the number of free parameters we find that
a flat prior on the scale of inflation (which is to be distinguished from a
flat prior on the tensor-to-scalar ratio) leads us to infer a larger, and in
fact slightly nonzero tensor contribution at 68% confidence level. However, no
detection is claimed. Our results demonstrate that all that is statistically
relevant at the current time is the (slightly enhanced) upper bound on r, and
we stress that the data remain consistent with r = 0.Comment: 9 pages, 5 figures. Section added on Bayesian complexity. Matches
published versio
Features and New Physical Scales in Primordial Observables: Theory and Observation
All cosmological observations to date are consistent with adiabatic, Gaussian
and nearly scale invariant initial conditions. These findings provide strong
evidence for a particular symmetry breaking pattern in the very early universe
(with a close to vanishing order parameter, ), widely accepted as
conforming to the predictions of the simplest realizations of the inflationary
paradigm. However, given that our observations are only privy to perturbations,
in inferring something about the background that gave rise to them, it should
be clear that many different underlying constructions project onto the same set
of cosmological observables. Features in the primordial correlation functions,
if present, would offer a unique and discriminating window onto the parent
theory in which the mechanism that generated the initial conditions is
embedded. In certain contexts, simple linear response theory allows us to infer
new characteristic scales from the presence of features that can break the
aforementioned degeneracies among different background models, and in some
cases can even offer a limited spectroscopy of the heavier degrees of freedom
that couple to the inflaton. In this review, we offer a pedagogical survey of
the diverse, theoretically well grounded mechanisms which can imprint features
into primordial correlation functions in addition to reviewing the techniques
one can employ to probe observations. These observations include cosmic
microwave background anisotropies and spectral distortions as well as the
matter two and three point functions as inferred from large-scale structure and
potentially, 21 cm surveys.Comment: Invited review to IJMPD, 101 pages + 2 appendices, 29 figures,
references added, matches journal versio
Getting leverage on inflation with a large photometric redshift survey
We assess the potential of a future large-volume photometric redshift survey
to constrain observational inflationary parameters using three large-scale
structure observables: the angular shear and galaxy power spectra, and the
cluster mass function measured through weak lensing. When used in combination
with Planck-like CMB measurements, we find that the spectral index n_s can be
constrained to a 1 sigma precision of up to 0.0025. The sensitivity to the
running of the spectral index can potentially improve to 0.0017, roughly a
factor of five better than the present 1 sigma~constraint from Planck and
auxiliary CMB data, allowing us to test the assumptions of the slow-roll
scenario with unprecedented accuracy. Interestingly, neither CMB+shear nor
CMB+galaxy nor CMB+clusters alone can achieve this level of sensitivity; it is
the combined power of all three probes that conspires to break the different
parameter degeneracies inherent in each type of observations. We make our
forecast software publicly available via download or upon request from the
authors.Comment: 22 pages, 6 figures; the forecast software can be downloaded from
http://jhamann.web.cern.ch/jhamann/simdata/simdata.tar.g
Constraining primordial tensor features with the anisotropies of the Cosmic Microwave Background
It is commonly assumed that the stochastic background of gravitational waves
on cosmological scales follows an almost scale-independent power spectrum, as
generically predicted by the inflationary paradigm. However, it is not
inconceivable that the spectrum could have strongly scale-dependent features,
generated, e.g., via transient dynamics of spectator axion-gauge fields during
inflation. Using the temperature and polarisation maps from the \textit{Planck}
and BICEP/Keck datasets, we search for such features, taking the example of a
log-normal bump in the primordial tensor spectrum at CMB scales. We do not find
any evidence for the existence of bump-like tensor features at present, but
demonstrate that future CMB experiments such as LiteBIRD and CMB-S4 will
greatly improve our prospects of determining the amplitude, location and width
of such a bump. We also highlight the role of delensing in constraining these
features at angular scales .Comment: 16 pages, 7 figure
A Minkowski Functional Analysis of the Cosmic Microwave Background Weak Lensing Convergence
Minkowski functionals are summary statistics that capture the geometric and
morphological properties of fields. They are sensitive to all higher order
correlations of the fields and can be used to complement more conventional
statistics, such as the power spectrum of the field. We develop a Minkowski
functional-based approach for a full likelihood analysis of mildly non-Gaussian
sky maps with partial sky coverage. Applying this to the inference of
cosmological parameters from the Planck mission's map of the Cosmic Microwave
Background's lensing convergence, we find an excellent agreement with results
from the power spectrum-based lensing likelihood. While the non-Gaussianity of
current CMB lensing maps is dominated by reconstruction noise, a Minkowski
functional-based analysis may be able to extract cosmological information from
the non-Gaussianity of future lensing maps and thus go beyond what is
accessible with a power spectrum-based analysis. We make the numerical code for
the calculation of a map's Minkowski functionals, skewness and kurtosis
parameters available for download from GitHub.Comment: 22 pages, 13 figure
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