308 research outputs found
The promising future of a robust cosmological neutrino mass measurement
We forecast the sensitivity of thirty-five different combinations of future
Cosmic Microwave Background and Large Scale Structure data sets to cosmological
parameters and to the total neutrino mass. We work under conservative
assumptions accounting for uncertainties in the modelling of systematics. In
particular, for galaxy redshift surveys, we remove the information coming from
non-linear scales. We use Bayesian parameter extraction from mock likelihoods
to avoid Fisher matrix uncertainties. Our grid of results allows for a direct
comparison between the sensitivity of different data sets. We find that future
surveys will measure the neutrino mass with high significance and will not be
substantially affected by potential parameter degeneracies between neutrino
masses, the density of relativistic relics, and a possible time-varying
equation of state of Dark Energy.Comment: 27 pages, 4 figures, 8 tables. v2: updated Euclid sensitivity
settings, matches published versio
Cosmology in the era of Euclid and the Square Kilometre Array
Theoretical uncertainties on non-linear scales are among the main obstacles
to exploit the sensitivity of forthcoming galaxy and hydrogen surveys like
Euclid or the Square Kilometre Array (SKA). Here, we devise a new method to
model the theoretical error that goes beyond the usual cut-off on small scales.
The advantage of this more efficient implementation of the non-linear
uncertainties is tested through a Markov-Chain-Monte-Carlo (MCMC) forecast of
the sensitivity of Euclid and SKA to the parameters of the standard
CDM model, including massive neutrinos with total mass , and to
3 extended scenarios, including 1) additional relativistic degrees of freedom
(CDM + + ), 2) a deviation from the
cosmological constant (CDM + + ), and 3) a time-varying
dark energy equation of state parameter (CDM + +
). We compare the sensitivity of 14 different
combinations of cosmological probes and experimental configurations. For Euclid
combined with Planck, assuming a plain cosmological constant, our method gives
robust predictions for a high sensitivity to the primordial spectral index
(), the Hubble constant
(), the total neutrino mass
(). Assuming dynamical dark energy we get
for the mass and for the equation of state parameters. The predicted
sensitivity to is mostly stable against the extensions of the
cosmological model considered here. Interestingly, a significant improvement of
the constraints on the extended model parameters is also obtained when
combining Euclid with a low redshift HI intensity mapping survey by SKA1,
demonstrating the importance of the synergy of Euclid and SKA.Comment: 50 pages, 11 figures, 8 tables. v2: improved treatment of neutrino.
v3: updated Euclid sensitivity settings, matches accepted versio
The - Diagram: Transforming pulsar scintillation spectra to coordinates on highly anisotropic interstellar scattering screens
We introduce a novel analysis technique for pulsar secondary spectra. The
power spectrum of pulsar scintillation (referred to as the "secondary
spectrum") shows differential delays and Doppler shifts due to interference
from multi-path propagation through the interstellar medium. We develop a
transformation which maps these observables to angular coordinates on a single
thin screen of phase-changing material. This transformation is possible without
degeneracies in the case of a one-dimensional distribution of images on this
screen, which is often a successful description of the phenomenon. The double
parabolic features of secondary spectra are transformed into parallel linear
features, whose properties we describe in detail. Furthermore, we introduce
methods to measure the curvature parameter and the field amplitude distribution
of images by applying them to observations of PSR B0834+06. Finally, we extend
this formalism to two-dimensional distributions of images on the interstellar
screen.Comment: 11 pages, 14 figures, 1 table, v2: matches accepted versio
Bias due to neutrinos must not uncorrect'd go
In cosmologies with massive neutrinos, the galaxy bias defined with respect
to the total matter field (cold dark matter, baryons, and non-relativistic
neutrinos) depends on the sum of the neutrino masses , and becomes
scale-dependent even on large scales. This effect has been usually neglected
given the sensitivity of current surveys, but becomes a severe systematic for
future surveys aiming to provide the first detection of non-zero . The
effect can be corrected for by defining the bias with respect to the density
field of cold dark matter and baryons instead of the total matter field. In
this work, we provide a simple prescription for correctly mitigating the
neutrino-induced scale-dependent bias effect in a practical way. We clarify a
number of subtleties regarding how to properly implement this correction in the
presence of redshift-space distortions and non-linear evolution of
perturbations. We perform a MCMC analysis on simulated galaxy clustering data
that match the expected sensitivity of the \textit{Euclid} survey. We find that
the neutrino-induced scale-dependent bias can lead to important shifts in both
the inferred mean value of , as well as its uncertainty. We show how
these shifts propagate to other cosmological parameters correlated with
, such as the cold dark matter physical density and
the scalar spectral index . In conclusion, we find that correctly
accounting for the neutrino-induced scale-dependent bias will be of crucial
importance for future galaxy clustering analyses. We encourage the cosmology
community to correctly account for this effect using the simple prescription we
present in our work. The tools necessary to easily correct for the
neutrino-induced scale-dependent bias will be made publicly available in an
upcoming release of the Boltzmann solver \texttt{CLASS}.Comment: 12 pages, 2 figures, abstract abridged. Version accepted for
publication in JCAP. The busy reader should skip to Sec. IID, V, and the
figures. A "Note added" between conclusions and acknowledgements explains our
choice of titl
Digital reality: a model-based approach to supervised learning from synthetic data
Hierarchical neural networks with large numbers of layers are the state of the art for most computer vision problems including image classification, multi-object detection and semantic segmentation. While the computational demands of training such deep networks can be addressed using specialized hardware, the availability of training data in sufficient quantity and quality remains a limiting factor. Main reasons are that measurement or manual labelling are prohibitively expensive, ethical considerations can limit generating data, or a phenomenon in questions has been predicted, but not yet observed. In this position paper, we present the Digital Reality concept are a structured approach to generate training data synthetically. The central idea is to simulate measurements based on scenes that are generated by parametric models of the real world. By investigating the parameter space defined of such models, training data can be generated in a controlled way compared to data that was captured from real world situations. We propose the Digital Reality concept and demonstrate its potential in different application domains, including industrial inspection, autonomous driving, smart grid, and microscopy research in material science and engineering
Interstellar Interferometry: Precise Curvature Measurement from Pulsar Secondary Spectra
The parabolic structure of the secondary or conjugate spectra of pulsars is
often the result of isolated one-dimensional (or at least highly anisotropic)
lenses in the ISM. The curvature of these features contains information about
the velocities of the Earth, ISM, and pulsar along the primary axis of the
lens. As a result, measuring variations in the curvature over the course of a
year, or the orbital period for pulsars in binaries, can constrain properties
of the screen and pulsar. In particular the pulsar distance and orbital
inclination for binary systems can be found for multiple screens or systems
with prior information on . By mapping the conjugate spectra into a
space where the main arc and inverted arclets are straight lines, we are able
to make use of the full information content from the inverted arclet
curvatures, amplitudes, and phases using eigenvectors to uniquely and optimally
retrieve phase information. This allows for a higher precision measurement than
the standard Hough transform for systems where these features are available.
Our technique also directly yields the best fit 1D impulse response function
for the interstellar lens given in terms of the Doppler shift, time delay, and
magnification of images on the sky as seen from a single observatory. This can
be extended for use in holographic imaging of the lens by combining multiple
telescopes. We present examples of this new method for both simulated data and
actual observations of PSR B0834+06
Multi-shot Echo Planar Imaging for accelerated Cartesian MR Fingerprinting: An alternative to conventional spiral MR Fingerprinting.
PURPOSE: To develop an accelerated Cartesian MRF implementation using a multi-shot EPI sequence for rapid simultaneous quantification of T1 and T2 parameters. METHODS: The proposed Cartesian MRF method involved the acquisition of highly subsampled MR images using a 16-shot EPI readout. A linearly varying flip angle train was used for rapid, simultaneous T1 and T2 quantification. The results were compared to a conventional spiral MRF implementation. The acquisition time per slice was 8s and this method was validated on two different phantoms and three healthy volunteer brains in vivo. RESULTS: Joint T1 and T2 estimations using the 16-shot EPI readout are in good agreement with the spiral implementation using the same acquisition parameters (<4% deviation for T1 and <6% deviation for T2). The T1 and T2 values also agree with the conventional values previously reported in the literature. The visual qualities of fine brain structures in the multi-parametric maps generated by multi-shot EPI-MRF and Spiral-MRF implementations were comparable. CONCLUSION: The multi-shot EPI-MRF method generated accurate quantitative multi-parametric maps similar to conventional Spiral-MRF. This multi-shot approach achieved considerable k-space subsampling and comparatively short TRs in a similar manner to spirals and therefore provides an alternative for performing MRF using an accelerated Cartesian readout; thereby increasing the potential usability of MRF.The research leading to these results has received funding from the European Commission H2020 Framework Programme (H2020- MSCAITN- 2014), number 642685 MacSeNet, the Engineering and Physical Sciences Research Council (EPSRC) platform Compressed Quantitative MRI grant, number EP/M019802/1 and the Scottish Research Partnership in Engineering (SRPe) award, number SRPe PECRE1718/ 17
IMILAST: a community effort to intercompare extratropical cyclone detection and tracking algorithms
The variability of results from different automated methods of detection and tracking of extratropical cyclones is assessed in order to identify uncertainties related to the choice of method. Fifteen international teams applied their own algorithms to the same dataset—the period 1989–2009 of interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERAInterim) data. This experiment is part of the community project Intercomparison of Mid Latitude Storm Diagnostics (IMILAST; see www.proclim.ch/imilast/index.html). The spread of results for cyclone frequency, intensity, life cycle, and track location is presented to illustrate the impact of using different methods. Globally, methods agree well for geographical distribution in large oceanic regions, interannual variability of cyclone numbers, geographical patterns of strong trends, and distribution shape for many life cycle characteristics. In contrast, the largest disparities exist for the total numbers of cyclones, the detection of weak cyclones, and distribution in some densely populated regions. Consistency between methods is better for strong cyclones than for shallow ones. Two case studies of relatively large, intense cyclones reveal that the identification of the most intense part of the life cycle of these events is robust between methods, but considerable differences exist during the development and the dissolution phases
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