30 research outputs found
Separate Constraints on Early and Late Cosmology
Since the public release of Planck data, several attempts have been made to
explain the observed small tensions with other data-sets, most of them
involving an extension of the {\Lambda}CDM Model. We try here an alternative
approach to the data analysis, based on separating the constraints coming from
the different epochs in cosmology, in order to assess which part of the
Standard Model generates the tension with the data. To this end, we perform a
particular analysis of Planck data probing only the early cosmological
evolution, until the time of photon decoupling. Then, we utilise this result to
see if the {\Lambda}CDM model can fit all observational constraints probing
only the late cosmological background evolution, discarding any information
concerning the late perturbation evolution. We find that all tensions between
the datasets are removed, suggesting that our standard assumptions on the
perturbed late-time history, as well as on reionisation, could sufficiently
bias our parameter extraction and be the source of the alleged tensions.Comment: 6 pages, 3 figure
Strongest model-independent bound on the lifetime of Dark Matter
Dark Matter is essential for structure formation in the late Universe so it
must be stable on cosmological time scales. But how stable exactly? Only
assuming decays into relativistic particles, we report an otherwise model
independent bound on the lifetime of Dark Matter using current cosmological
data. Since these decays affect only the low- multipoles of the CMB, the
Dark Matter lifetime is expected to correlate with the tensor-to-scalar ratio
as well as curvature . We consider two models, including and
respectively, versus data from Planck, WMAP, WiggleZ and Baryon
Acoustic Oscillations, with or without the BICEP2 data (if interpreted in terms
of primordial gravitational waves). This results in a lower bound on the
lifetime of CDM given by 160Gyr (without BICEP2) or 200Gyr (with BICEP2) at 95%
confidence level.Comment: 15 pages, 5 figures. Prepared for submission to JCA
Neutrino and Dark Matter Properties from Cosmological Observations
We apply the principles of Bayesian statistics to the main probes of cosmology, in order to refine our knowledge of the Standard Model and possibly extend it. Notably, we investigate the basic elements of the model in detail in order to reinforce this basic foundation of the field, and lay down a systematic way of obtaining model-independent constraints on parts of the Standard Model. We further try to constrain some of the unknown properties of Dark Matter, namely its decay or annihilation rates, to help reducing the range of possibilities for model builders. By using recent cosmological probes and making as little assumptions as possible, we are able to meaningfully constrain these properties in the prospect of narrowing down a particle physics search. Eventually, we show how future experiments will be able to put strong bounds on the neutrino total mass, as long as the theoretical uncertainty is handled carefully. Despite being cautiously pessimistic, we prove how EUCLID will be able to detect even the lowest possible allowed neutrino mass, by simply using properly the linear scales. We also show the target precision for the theoretical prediction in order to make full use of the forthcoming wealth of data at mildly non-linear scales
Non-linear matter power spectrum from Time Renormalisation Group: efficient computation and comparison with one-loop
We address the issue of computing the non-linear matter power spectrum on
mildly non-linear scales with efficient semi-analytic methods. We implemented
M. Pietroni's Time Renormalization Group (TRG) method and its Dynamical 1-Loop
(D1L) limit in a numerical module for the new Boltzmann code CLASS. Our
publicly released module is valid for LCDM models, and optimized in such a way
to run in less than a minute for D1L, or in one hour (divided by number of
nodes) for TRG. A careful comparison of the D1L, TRG and Standard 1-Loop
approaches reveals that results depend crucially on the assumed initial
bispectrum at high redshift. When starting from a common assumption, the three
methods give roughly the same results, showing that the partial resumation of
diagrams beyond one loop in the TRG method improves one-loop results by a
negligible amount. A comparison with highly accurate simulations by M. Sato &
T. Matsubara shows that all three methods tend to over-predict non-linear
corrections by the same amount on small wavelengths. Percent precision is
achieved until k~0.2 h/Mpc for z>2, or until k~0.14 h/Mpc at z=1.Comment: 24 pages, 7 figures, revised title and conclusions, version accepted
in JCAP, code available at http://class-code.ne
CMB photons shedding light on dark matter
The annihilation or decay of Dark Matter (DM) particles could affect the
thermal history of the universe and leave an observable signature in Cosmic
Microwave Background (CMB) anisotropies. We update constraints on the
annihilation rate of DM particles in the smooth cosmological background, using
WMAP7 and recent small-scale CMB data. With a systematic analysis based on the
Press-Schechter formalism, we also show that DM annihilation in halos at small
redshift may explain entirely the reionization patterns observed in the CMB,
under reasonable assumptions concerning the concentration and formation
redshift of halos. We find that a mixed reionization model based on DM
annihilation in halos as well as star formation at a redshift z~6.5 could
simultaneously account for CMB observations and satisfy constraints inferred
from the Gunn-Peterson effect. However, these models tend to reheat the
inter-galactic medium (IGM) well above observational bounds: by including a
realistic prior on the IGM temperature at low redshift, we find stronger
cosmological bounds on the annihilation cross-section than with the CMB alone.Comment: 35 pages, 14 figures; version accepted in JCAP after minor revision
Robustness of cosmic neutrino background detection in the cosmic microwave background
The existence of a cosmic neutrino background can be probed indirectly by CMB experiments, not only by measuring the background density of radiation in the universe, but also by searching for the typical signatures of the fluctuations of free-streaming species in the temperature and polarisation power spectrum. Previous studies have already proposed a rather generic parametrisation of these fluctuations, that could help to discriminate between the signature of ordinary free-streaming neutrinos, or of more exotic dark radiation models. Current data are compatible with standard values of these parameters, which seems to bring further evidence for the existence of a cosmic neutrino background. In this work, we investigate the robustness of this conclusion under various assumptions. We generalise the definition of an effective sound speed and viscosity speed to the case of massive neutrinos or other dark radiation components experiencing a non-relativistic transition. We show that current bounds on these effective parameters do not vary significantly when considering an arbitrary value of the particle mass, or extended cosmological models with a free effective neutrino number, dynamical dark energy or a running of the primordial spectrum tilt. We conclude that it is possible to make a robust statement about the detection of the cosmic neutrino background by CMB experiments
KiDS-450: the tomographic weak lensing power spectrum and constraints on cosmological parameters
We present measurements of the weak gravitational lensing shear power
spectrum based on sq. deg. of imaging data from the Kilo Degree Survey.
We employ a quadratic estimator in two and three redshift bins and extract band
powers of redshift auto-correlation and cross-correlation spectra in the
multipole range . The cosmological interpretation of
the measured shear power spectra is performed in a Bayesian framework assuming
a CDM model with spatially flat geometry, while accounting for small
residual uncertainties in the shear calibration and redshift distributions as
well as marginalising over intrinsic alignments, baryon feedback and an
excess-noise power model. Moreover, massive neutrinos are included in the
modelling. The cosmological main result is expressed in terms of the parameter
combination yielding $S_8 = \
0.651 \pm 0.0583.2\sigma$ (3 z-bins). We
cross-check the results of the 3 z-bin analysis with the weaker constraints
from the 2 z-bin analysis and find them to be consistent. The high-level data
products of this analysis, such as the band power measurements, covariance
matrices, redshift distributions, and likelihood evaluation chains are
available at http://kids.strw.leidenuniv.nl/Comment: 23 pages, 18 figures, 5 tables; results unchanged, version accepted
for publication by MNRAS. Data products available at
http://kids.strw.leidenuniv.nl
Peri-operative red blood cell transfusion in neonates and infants: NEonate and Children audiT of Anaesthesia pRactice IN Europe: A prospective European multicentre observational study
BACKGROUND: Little is known about current clinical practice concerning peri-operative red blood cell transfusion in neonates and small infants. Guidelines suggest transfusions based on haemoglobin thresholds ranging from 8.5 to 12âgâdl-1, distinguishing between children from birth to day 7 (week 1), from day 8 to day 14 (week 2) or from day 15 (â„week 3) onwards. OBJECTIVE: To observe peri-operative red blood cell transfusion practice according to guidelines in relation to patient outcome. DESIGN: A multicentre observational study. SETTING: The NEonate-Children sTudy of Anaesthesia pRactice IN Europe (NECTARINE) trial recruited patients up to 60 weeks' postmenstrual age undergoing anaesthesia for surgical or diagnostic procedures from 165 centres in 31 European countries between March 2016 and January 2017. PATIENTS: The data included 5609 patients undergoing 6542 procedures. Inclusion criteria was a peri-operative red blood cell transfusion. MAIN OUTCOME MEASURES: The primary endpoint was the haemoglobin level triggering a transfusion for neonates in week 1, week 2 and week 3. Secondary endpoints were transfusion volumes, 'delta haemoglobin' (preprocedure - transfusion-triggering) and 30-day and 90-day morbidity and mortality. RESULTS: Peri-operative red blood cell transfusions were recorded during 447 procedures (6.9%). The median haemoglobin levels triggering a transfusion were 9.6 [IQR 8.7 to 10.9] gâdl-1 for neonates in week 1, 9.6 [7.7 to 10.4] gâdl-1 in week 2 and 8.0 [7.3 to 9.0] gâdl-1 in week 3. The median transfusion volume was 17.1 [11.1 to 26.4] mlâkg-1 with a median delta haemoglobin of 1.8 [0.0 to 3.6] gâdl-1. Thirty-day morbidity was 47.8% with an overall mortality of 11.3%. CONCLUSIONS: Results indicate lower transfusion-triggering haemoglobin thresholds in clinical practice than suggested by current guidelines. The high morbidity and mortality of this NECTARINE sub-cohort calls for investigative action and evidence-based guidelines addressing peri-operative red blood cell transfusions strategies. TRIAL REGISTRATION: ClinicalTrials.gov, identifier: NCT02350348
Robustness of cosmic neutrino background detection in the cosmic microwave background
The existence of a cosmic neutrino background can be probed indirectly by CMB
experiments, not only by measuring the background density of radiation in the
universe, but also by searching for the typical signatures of the fluctuations
of free-streaming species in the temperature and polarisation power spectrum.
Previous studies have already proposed a rather generic parametrisation of
these fluctuations, that could help to discriminate between the signature of
ordinary free-streaming neutrinos, or of more exotic dark radiation models.
Current data are compatible with standard values of these parameters, which
seems to bring further evidence for the existence of a cosmic neutrino
background. In this work, we investigate the robustness of this conclusion
under various assumptions. We generalise the definition of an effective sound
speed and viscosity speed to the case of massive neutrinos or other dark
radiation components experiencing a non-relativistic transition. We show that
current bounds on these effective parameters do not vary significantly when
considering an arbitrary value of the particle mass, or extended cosmological
models with a free effective neutrino number, dynamical dark energy or a
running of the primordial spectrum tilt. We conclude that it is possible to
make a robust statement about the detection of the cosmic neutrino background
by CMB experiments.Comment: version accepted for publication in JCAP. 19 pages, 7 figures, 3
tables. Minor changes. References adde