1,157 research outputs found
Quantifying Tensions between CMB and Distance Datasets in Models with Free Curvature or Lensing Amplitude
Recent measurements of the Cosmic Microwave Background (CMB) by the Planck
Collaboration have produced arguably the most powerful observational evidence
in support of the standard model of cosmology, i.e. the spatially flat
CDM paradigm. In this work, we perform model selection tests to
examine whether the base CMB temperature and large scale polarization
anisotropy data from Planck 2015 (P15) prefer any of eight commonly used
one-parameter model extensions with respect to flat CDM. We find a
clear preference for models with free curvature, , or free
amplitude of the CMB lensing potential, . We also further develop
statistical tools to measure tension between datasets. We use a Gaussianization
scheme to compute tensions directly from the posterior samples using an
entropy-based method, the surprise, as well as a calibrated evidence ratio
presented here for the first time. We then proceed to investigate the
consistency between the base P15~CMB data and six other CMB and distance
datasets. In flat CDM we find a tension between the base
P15~CMB data and a distance ladder measurement, whereas the former are
consistent with the other datasets. In the curved CDM model we find
significant tensions in most of the cases, arising from the well-known low
power of the low- multipoles of the CMB data. In the flat CDM
model, however, all datasets are consistent with the base
P15~CMB observations except for the CMB lensing measurement, which remains in
significant tension. This tension is driven by the increased power of the CMB
lensing potential derived from the base P15~CMB constraints in both models,
pointing at either potentially unresolved systematic effects or the need for
new physics beyond the standard flat CDM model.Comment: 16 pages, 8 figures, 6 table
Reconstructing the Local Potential of Inflation with BICEP2 data
We locally reconstruct the inflationary potential by using the current
constraints on and from BICEP2 data. Assuming small and
negligible , the inflationary potential is approximately linear
in range but becomes non-linear in range. However if we vary the value of within
the range given by constraints from {\it Planck} measurement, the local
reconstruction is only valid in the range of ,
which challenges the inflationary background from the point of view of
effective field theory. We show that, within the range of , the inflation potential can be precisely reconstructed. With the
current reconstruction, we show that and are
consistent, while model is ruled out by confidence level of the
reconstructed range of potential. This sets up a strong limit of large-field
inflation models.Comment: 11 pages, 10 figure
Statistical anisotropy as a consequence of inflation
Cosmological inflation remains to be a unique mechanism of generation of
plausible initial conditions in the early universe. In particular, it generates
the primordial quasiclassical perturbations with power spectrum determined by
the fundamental principles of quantum field theory. In this work, we pay
attention to the fact that the quasiclassical perturbations permanently
generated at early stages of inflation break homogeneity and isotropy of the
cosmological background. The evolution of the small-scale quantum vacuum modes
on this inhomogeneous background results in statistical anisotropy of the
primordial power spectrum, which can manifest itself in the observable
large-scale structure and cosmic microwave background. The effect is predicted
to have almost scale-invariant form dominated by a quadrupole and may serve as
a non-trivial test of the inflationary scenario. Theoretical expectation of the
magnitude of this statistical anisotropy depends on the assumptions about the
physics in the trans-Planckian region of wavenumbers.Comment: 7 pages, Proceedings of the Grassmannian Conference in Fundamental
Cosmology, September 14--19, 2009, Szczecin, Polan
Inhomogeneity-induced variance of cosmological parameters
Modern cosmology relies on the assumption of large-scale isotropy and
homogeneity of the Universe. However, locally the Universe is inhomogeneous and
anisotropic. So, how can local measurements (at the 100 Mpc scale) be used to
determine global cosmological parameters (defined at the 10 Gpc scale)? We use
Buchert's averaging formalism and determine a set of locally averaged
cosmological parameters in the context of the flat Lambda cold dark matter
model. We calculate their ensemble means (i.e. their global values) and
variances (i.e. their cosmic variances). We apply our results to typical survey
geometries and focus on the study of the effects of local fluctuations of the
curvature parameter. By this means we show, that in the linear regime
cosmological backreaction and averaging can be reformulated as the issue of
cosmic variance. The cosmic variance is found largest for the curvature
parameter and discuss some of its consequences. We further propose to use the
observed variance of cosmological parameters to measure the growth factor.
[abbreviated]Comment: 12 pages, 10 figures, references added, estimate of lightcone effects
added, matches version published in A&
The XMM Cluster Survey: Forecasting cosmological and cluster scaling-relation parameter constraints
We forecast the constraints on the values of sigma_8, Omega_m, and cluster
scaling relation parameters which we expect to obtain from the XMM Cluster
Survey (XCS). We assume a flat Lambda-CDM Universe and perform a Monte Carlo
Markov Chain analysis of the evolution of the number density of galaxy clusters
that takes into account a detailed simulated selection function. Comparing our
current observed number of clusters shows good agreement with predictions. We
determine the expected degradation of the constraints as a result of
self-calibrating the luminosity-temperature relation (with scatter), including
temperature measurement errors, and relying on photometric methods for the
estimation of galaxy cluster redshifts. We examine the effects of systematic
errors in scaling relation and measurement error assumptions. Using only (T,z)
self-calibration, we expect to measure Omega_m to +-0.03 (and Omega_Lambda to
the same accuracy assuming flatness), and sigma_8 to +-0.05, also constraining
the normalization and slope of the luminosity-temperature relation to +-6 and
+-13 per cent (at 1sigma) respectively in the process. Self-calibration fails
to jointly constrain the scatter and redshift evolution of the
luminosity-temperature relation significantly. Additional archival and/or
follow-up data will improve on this. We do not expect measurement errors or
imperfect knowledge of their distribution to degrade constraints significantly.
Scaling-relation systematics can easily lead to cosmological constraints 2sigma
or more away from the fiducial model. Our treatment is the first exact
treatment to this level of detail, and introduces a new `smoothed ML' estimate
of expected constraints.Comment: 28 pages, 17 figures. Revised version, as accepted for publication in
MNRAS. High-resolution figures available at http://xcs-home.org (under
"Publications"
Novel approaches to modelling and monitoring of heavy metal - contaminated sites
Soil contamination is becoming more prevalent, and with increasing global population, more people are being affected. Contaminated site assessment informs management of contaminant sources, affected soil and groundwater. Inaccuracy of assessment can lead to misclassification of sites, resulting in unnecessary remediation, or failing to remediate where it is required. The research presented in this thesis sought to reduce the risk of misclassification by addressing four key aspects of assessment; sampling, detection, mapping and monitoring. The study sought to refine sample size requirements by estimating the number of samples required to determine if the mean at a site exceeded Australian contamination thresholds. A large number of samples were required, yet this may be unrealistic due to time and cost. Portable X-ray Fluorescence spectroscopy (PXRF) provides real-time analysis of soil heavy metal concentrations, enabling more samples to be collected. There is room for improvement in the accuracy of PXRF measurements, so the study explored the potential of integrating these with spectra obtained from visible-near infrared spectroscopy (vis-NIR). Integration of the two spectral methods provided a measure of precision, yet only a marginal increase in accuracy. To improve mapping methods this study obtained measurements from within the Sydney estuary catchment and integrated these, alongside freely available covariates, into linear mixed models to predict lead and zinc concentrations in soil across the catchment. The final chapter of the thesis combined linear mixed models from two time points to predict change in heavy metal concentrations over time at a remediated Sydney parkland. The models provided a detailed snapshot of heavy metal distributions and factors influencing these distributions over time. It is evident in this thesis that much can be done to improve contaminated site assessment and help ensure land is safe and secured for future generations
Resonance fluorescence from an artificial atom in squeezed vacuum
We present an experimental realization of resonance fluorescence in squeezed
vacuum. We strongly couple microwave-frequency squeezed light to a
superconducting artificial atom and detect the resulting fluorescence with high
resolution enabled by a broadband traveling-wave parametric amplifier. We
investigate the fluorescence spectra in the weak and strong driving regimes,
observing up to 3.1 dB of reduction of the fluorescence linewidth below the
ordinary vacuum level and a dramatic dependence of the Mollow triplet spectrum
on the relative phase of the driving and squeezed vacuum fields. Our results
are in excellent agreement with predictions for spectra produced by a two-level
atom in squeezed vacuum [Phys. Rev. Lett. \textbf{58}, 2539-2542 (1987)],
demonstrating that resonance fluorescence offers a resource-efficient means to
characterize squeezing in cryogenic environments
Fluctuating pressures measured beneath a high-temperature, turbulent boundary layer on a flat plate at Mach number of 5
Fluctuating pressures were measured beneath a Mach 5, turbulent boundary layer on a flat plate with an array of piezoresistive sensors. The data were obtained with a digital signal acquisition system during a test run of 4 seconds. Data sampling rate was such that frequency analysis up to 62.5 kHz could be performed. To assess in situ frequency response of the sensors, a specially designed waveguide calibration system was employed to measure transfer functions of all sensors and related instrumentation. Pressure time histories were approximated well by a Gaussian prohibiting distribution. Pressure spectra were very repeatable over the array span of 76 mm. Total rms pressures ranged from 0.0017 to 0.0046 of the freestream dynamic pressure. Streamwise, space-time correlations exhibited expected decaying behavior of a turbulence generated pressure field. Average convection speed was 0.87 of freestream velocity. The trendless behavior with sensor separation indicated possible systematic errors
Spectral reflectivity of solid surfaces at low temperatures
Spectral reflectivity of solid surfaces at low temperature
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