48 research outputs found
Cosmological parameters from large scale structure - geometric versus shape information
The matter power spectrum as derived from large scale structure (LSS) surveys
contains two important and distinct pieces of information: an overall smooth
shape and the imprint of baryon acoustic oscillations (BAO). We investigate the
separate impact of these two types of information on cosmological parameter
estimation, and show that for the simplest cosmological models, the broad-band
shape information currently contained in the SDSS DR7 halo power spectrum (HPS)
is by far superseded by geometric information derived from the baryonic
features. An immediate corollary is that contrary to popular beliefs, the upper
limit on the neutrino mass m_\nu presently derived from LSS combined with
cosmic microwave background (CMB) data does not in fact arise from the possible
small-scale power suppression due to neutrino free-streaming, if we limit the
model framework to minimal LambdaCDM+m_\nu. However, in more complicated
models, such as those extended with extra light degrees of freedom and a dark
energy equation of state parameter w differing from -1, shape information
becomes crucial for the resolution of parameter degeneracies. This conclusion
will remain true even when data from the Planck surveyor become available. In
the course of our analysis, we introduce a new dewiggling procedure that allows
us to extend consistently the use of the SDSS HPS to models with an arbitrary
sound horizon at decoupling. All the cases considered here are compatible with
the conservative 95%-bounds \sum m_\nu < 1.16 eV, N_eff = 4.8 \pm 2.0.Comment: 18 pages, 4 figures; v2: references added, matches published versio
Sterile neutrinos with eV masses in cosmology -- how disfavoured exactly?
We study cosmological models that contain sterile neutrinos with eV-range
masses as suggested by reactor and short-baseline oscillation data. We confront
these models with both precision cosmological data (probing the CMB decoupling
epoch) and light-element abundances (probing the BBN epoch). In the minimal
LambdaCDM model, such sterile neutrinos are strongly disfavoured by current
data because they contribute too much hot dark matter. However, if the
cosmological framework is extended to include also additional relativistic
degrees of freedom -- beyond the three standard neutrinos and the putative
sterile neutrinos, then the hot dark matter constraint on the sterile states is
considerably relaxed. A further improvement is achieved by allowing a dark
energy equation of state parameter w<-1. While BBN strongly disfavours extra
radiation beyond the assumed eV-mass sterile neutrino, this constraint can be
circumvented by a small nu_e degeneracy. Any model containing eV-mass sterile
neutrinos implies also strong modifications of other cosmological parameters.
Notably, the inferred cold dark matter density can shift up by 20 to 75%
relative to the standard LambdaCDM value.Comment: 14 pages, 6 figures, v2: minor changes, matches version accepted for
publication in JCA
Measuring neutrino masses with a future galaxy survey
We perform a detailed forecast on how well a Euclid-like photometric galaxy
and cosmic shear survey will be able to constrain the absolute neutrino mass
scale. Adopting conservative assumptions about the survey specifications and
assuming complete ignorance of the galaxy bias, we estimate that the minimum
mass sum of sum m_nu ~ 0.06 eV in the normal hierarchy can be detected at 1.5
sigma to 2.5 sigma significance, depending on the model complexity, using a
combination of galaxy and cosmic shear power spectrum measurements in
conjunction with CMB temperature and polarisation observations from Planck.
With better knowledge of the galaxy bias, the significance of the detection
could potentially reach 5.4 sigma. Interestingly, neither Planck+shear nor
Planck+galaxy alone can achieve this level of sensitivity; it is the combined
effect of galaxy and cosmic shear power spectrum measurements that breaks the
persistent degeneracies between the neutrino mass, the physical matter density,
and the Hubble parameter. Notwithstanding this remarkable sensitivity to sum
m_nu, Euclid-like shear and galaxy data will not be sensitive to the exact mass
spectrum of the neutrino sector; no significant bias (< 1 sigma) in the
parameter estimation is induced by fitting inaccurate models of the neutrino
mass splittings to the mock data, nor does the goodness-of-fit of these models
suffer any significant degradation relative to the true one (Delta chi_eff ^2<
1).Comment: v1: 29 pages, 10 figures. v2: 33 pages, 12 figures; added sections on
shape evolution and constraints in more complex models, accepted for
publication in JCA
A Bayesian view of the current status of dark matter direct searches
Bayesian statistical methods offer a simple and consistent framework for
incorporating uncertainties into a multi-parameter inference problem. In this
work we apply these methods to a selection of current direct dark matter
searches. We consider the simplest scenario of spin-independent elastic WIMP
scattering, and infer the WIMP mass and cross-section from the experimental
data with the essential systematic uncertainties folded into the analysis. We
find that when uncertainties in the scintillation efficiency of Xenon100 have
been accounted for, the resulting exclusion limit is not sufficiently
constraining to rule out the CoGeNT preferred parameter region, contrary to
previous claims. In the same vein, we also investigate the impact of
astrophysical uncertainties on the preferred WIMP parameters. We find that
within the class of smooth and isotropic WIMP velocity distributions, it is
difficult to reconcile the DAMA and the CoGeNT preferred regions by tweaking
the astrophysics parameters alone. If we demand compatibility between these
experiments, then the inference process naturally concludes that a high value
for the sodium quenching factor for DAMA is preferred.Comment: 37 pages, 14 figures and 7 tables. Replacement for matching the
version accepted for publicatio
The Parallel Magnetoconductance of Interacting Electrons in a Two Dimensional Disordered System
The transport properties of interacting electrons for which the spin degree
of freedom is taken into account are numerically studied for small two
dimensional diffusive clusters. On-site electron-electron interactions tend to
delocalize the electrons, while long-range interactions enhance localization.
On careful examination of the transport properties, we reach the conclusion
that it does not show a two dimensional metal insulator transition driven by
interactions. A parallel magnetic field leads to enhanced resistivity, which
saturates once the electrons become fully spin polarized. The strength of the
magnetic field for which the resistivity saturates decreases as electron
density goes down. Thus, the numerical calculations capture some of the
features seen in recent experimental measurements of parallel
magnetoconductance.Comment: 10 pages, 6 figure
BOB CAT: a Large-Scale Review and Delphi Consensus for Management of Barrettâs Esophagus With No Dysplasia, Indefinite for, or Low-Grade Dysplasia
OBJECTIVES:
Barrettâs esophagus (BE) is a common premalignant lesion for which surveillance is recommended. This strategy is limited by considerable variations in clinical practice. We conducted an international, multidisciplinary, systematic search and evidence-based review of BE and provided consensus recommendations for clinical use in patients with nondysplastic, indefinite, and low-grade dysplasia (LGD).
METHODS:
We defined the scope, proposed statements, and searched electronic databases, yielding 20,558 publications that were screened, selected online, and formed the evidence base. We used a Delphi consensus process, with an 80% agreement threshold, using GRADE (Grading of Recommendations Assessment, Development and Evaluation) to categorize the quality of evidence and strength of recommendations.
RESULTS:
In total, 80% of respondents agreed with 55 of 127 statements in the final voting rounds. Population endoscopic screening is not recommended and screening should target only very high-risk cases of males aged over 60 years with chronic uncontrolled reflux. A new international definition of BE was agreed upon. For any degree of dysplasia, at least two specialist gastrointestinal (GI) pathologists are required. Risk factors for cancer include male gender, length of BE, and central obesity. Endoscopic resection should be used for visible, nodular areas. Surveillance is not recommended for <5 years of life expectancy. Management strategies for indefinite dysplasia (IND) and LGD were identified, including a de-escalation strategy for lower-risk patients and escalation to intervention with follow-up for higher-risk patients.
CONCLUSIONS:
In this uniquely large consensus process in gastroenterology, we made key clinical recommendations for the escalation/de-escalation of BE in clinical practice. We made strong recommendations for the prioritization of future research
Risk profiles and one-year outcomes of patients with newly diagnosed atrial fibrillation in India: Insights from the GARFIELD-AF Registry.
BACKGROUND: The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) is an ongoing prospective noninterventional registry, which is providing important information on the baseline characteristics, treatment patterns, and 1-year outcomes in patients with newly diagnosed non-valvular atrial fibrillation (NVAF). This report describes data from Indian patients recruited in this registry. METHODS AND RESULTS: A total of 52,014 patients with newly diagnosed AF were enrolled globally; of these, 1388 patients were recruited from 26 sites within India (2012-2016). In India, the mean age was 65.8 years at diagnosis of NVAF. Hypertension was the most prevalent risk factor for AF, present in 68.5% of patients from India and in 76.3% of patients globally (P < 0.001). Diabetes and coronary artery disease (CAD) were prevalent in 36.2% and 28.1% of patients as compared with global prevalence of 22.2% and 21.6%, respectively (P < 0.001 for both). Antiplatelet therapy was the most common antithrombotic treatment in India. With increasing stroke risk, however, patients were more likely to receive oral anticoagulant therapy [mainly vitamin K antagonist (VKA)], but average international normalized ratio (INR) was lower among Indian patients [median INR value 1.6 (interquartile range {IQR}: 1.3-2.3) versus 2.3 (IQR 1.8-2.8) (P < 0.001)]. Compared with other countries, patients from India had markedly higher rates of all-cause mortality [7.68 per 100 person-years (95% confidence interval 6.32-9.35) vs 4.34 (4.16-4.53), P < 0.0001], while rates of stroke/systemic embolism and major bleeding were lower after 1 year of follow-up. CONCLUSION: Compared to previously published registries from India, the GARFIELD-AF registry describes clinical profiles and outcomes in Indian patients with AF of a different etiology. The registry data show that compared to the rest of the world, Indian AF patients are younger in age and have more diabetes and CAD. Patients with a higher stroke risk are more likely to receive anticoagulation therapy with VKA but are underdosed compared with the global average in the GARFIELD-AF. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01090362
Partitioning the Heritability of Tourette Syndrome and Obsessive Compulsive Disorder Reveals Differences in Genetic Architecture
The direct estimation of heritability from genome-wide common variant data as implemented in the program Genome-wide Complex Trait Analysis (GCTA) has provided a means to quantify heritability attributable to all interrogated variants. We have quantified the variance in liability to disease explained