1,046 research outputs found
Can sterile neutrinos be the dark matter?
We use the Ly-alpha forest power spectrum measured by the SDSS and
high-resolution spectroscopy observations in combination with cosmic microwave
background and galaxy clustering constraints to place limits on a sterile
neutrino as a dark matter candidate in the warm dark matter (WDM) scenario.
Such a neutrino would be created in the early universe through mixing with an
active neutrino and would suppress structure on scales smaller than its free
streaming scale. We ran a series of high-resolution hydrodynamic simulations
with varying neutrino mass to describe the effect of a sterile neutrino on the
Ly-alpha forest power spectrum. We find that the mass limit is m_s >14 keV at
95% c.l. (10keV at 99.9%), which is nearly an order of magnitude tighter
constraint than previously published limits and is above the upper limit
allowed by X-ray constraints, excluding this candidate as dark matter in this
model. The corresponding limit for a neutrino that decoupled early while in
thermal equilibrium is 2.5keV (95% c.l.).Comment: 4 pages, 2 figures, submitted to PR
Dependence of the non-linear mass power spectrum on the equation of state of dark energy
We present N-body simulation calculations of the dependence of the power
spectrum of non-linear cosmological mass density fluctuations on the equation
of state of the dark energy, w=p/rho. At fixed linear theory power, increasing
w leads to an increase in non-linear power, with the effect increasing with k.
By k=10 h/Mpc, a model with w=-0.75 has ~12% more power than a standard
cosmological constant model (w=-1), while a model with w=-0.5 has ~33% extra
power (at z=0). The size of the effect increases with increasing dark energy
fraction, and to a lesser extent increasing power spectrum normalization, but
is insensitive to the power spectrum shape (the numbers above are for
Omega_m=0.281 and sigma_8=0.897). A code quantifying the non-linear effect of
varying w, as a function of k, z, and other cosmological parameters, which
should be accurate to a few percent for k<10 h/Mpc for models that fit the
current observations, is available at
http://www.cita.utoronto.ca/~pmcdonal/code.html. This paper also serves as an
example of a detailed exploration of the numerical convergence properties of
ratios of power spectra for different models, which can be useful because some
kinds of numerical error cancel in a ratio. When precision calculations based
on numerical simulations are needed for many different models, efficiency may
be gained by breaking the problem into a calculation of the absolute prediction
at a central point, and calculations of the relative change in the prediction
with model parameters.Comment: accepted by MNRAS, code at
http://www.cita.utoronto.ca/~pmcdonal/code.html, corrected error in plotting
Smith et al. prediction - now agree perfectly when w=-
Radiative Transfer Modeling of Lyman Alpha Emitters. II. New Effects in Galaxy Clustering
We study the clustering properties of z~5.7 Lyman-alpha emitters (LAEs) in a
cosmological reionization simulation with a full Lya radiative transfer
calculation. Lya radiative transfer substantially modifies the intrinsic Lya
emission properties, compared to observed ones, depending on the density and
velocity structure environment around the Lya emitting galaxy. This
environment-dependent Lya selection introduces new features in LAE clustering,
suppressing (enhancing) the line-of-sight (transverse) density fluctuations and
giving rise to scale-dependent galaxy bias. In real space, the contours of the
three-dimensional two-point correlation function of LAEs appear to be
prominently elongated along the line of sight on large scales, an effect that
is opposite to and much stronger than the linear redshift-space distortion
effect. The projected two-point correlation function is greatly enhanced in
amplitude by a factor of up to a few, compared to the case without the
environment dependent selection effect. The new features in LAE clustering can
be understood with a simple, physically motivated model, where Lya selection
depends on matter density, velocity, and their gradients. We discuss the
implications and consequences of the effects on galaxy clustering from Lya
selection in interpreting clustering measurements and in constraining cosmology
and reionization from LAEs.Comment: 31 pages, 26 figures, revised according to the referee's comments,
more discussions and tests, published in Ap
Imprint of Inhomogeneous Hydrogen Reionization on the Temperature Distribution of the Intergalactic Medium
We study the impact of inhomogeneous hydrogen reionization on the thermal
evolution of the intergalactic medium (IGM) using hydrodynamic + radiative
transfer simulations where reionization is completed either early (z ~ 9) or
late (z ~ 6). In general, we find that low-density gas near large-scale
overdensities is ionized and heated earlier than gas in the large-scale,
underdense voids. Furthermore, at a later time the IGM temperature is inversely
related to the reionization redshift because gas that is heated earlier has
more time to cool through adiabatic expansion and Compton scattering. Thus, at
the end of reionization the median temperature-density relation is an inverted
power-law with slope gamma-1 ~ -0.2, in both models. However, at fixed density,
there is up to order unity scatter in the temperature due to the distribution
of reionization redshifts. Because of the complex equation-of-state, the
evolved IGM temperature-density relations for the redshift range 4 < z < 6 can
still have significant curvature and scatter. These features must be taken into
account when interpreting the Lyman alpha absorption in high redshift quasar
spectra.Comment: 4 pages, 5 figures, accepted by ApJ Letter
Expression of chemokine receptors on peripheral blood lymphocytes in multiple sclerosis and neuromyelitis optica
<p>Abstract</p> <p>Background</p> <p>The role of different chemokine receptors in the pathogenesis of multiple sclerosis (MS) has been extensively investigated; however, little is known about the difference in the role of chemokine receptors between the pathogenesis of neuromyelitis optica (NMO) and MS. Therefore, we examined the expression of chemokine receptors on peripheral blood lymphocytes (PBL) in MS and NMO.</p> <p>Methods</p> <p>We used flow cytometry to analyse lymphocyte subsets in 12 patients with relapsing NMO, 24 with relapsing-remitting MS during relapse, 3 with NMO and 5 with MS during remission.</p> <p>Results</p> <p>Compared with healthy controls (HC), the percentage of lymphocytes in white blood cells was significantly lower in NMO and MS patients. The percentage of T cells expressing CD4<sup>+</sup>CD25<sup>+ </sup>and CD4<sup>+</sup>CD45RO<sup>+ </sup>was higher, while that of CD4<sup>+</sup>CC chemokine receptor (CCR)3<sup>+ </sup>(T helper 2, Th2) was significantly lower in MS patients than in HC. The ratios of CD4<sup>+</sup>CXC chemokine receptors (CXCR)3<sup>+</sup>/CD4<sup>+</sup>CCR3<sup>+ </sup>(Th1/Th2) and CD8<sup>+</sup>CXCR3<sup>+</sup>/CD8<sup>+</sup>CCR4<sup>+ </sup>(T cytotoxic 1, Tc1/Tc2) were higher in MS patients than in HC. The percentage of CD8<sup>+</sup>CXCR3<sup>+ </sup>T cell (Tc1) and CD4<sup>+</sup>CXCR3<sup>+ </sup>T cell (Th1) decreased significantly during remission in MS patients (<it>P <</it>0.05). No significant differences were identified in the expression of the chemokine receptors on PBL in NMO patients compared with MS patients and HC.</p> <p>Conclusions</p> <p>Th1 dominance of chemokine receptors on blood T cells and the correlation between CXCR3<sup>+ </sup>T cell (Th1 and Tc1) and disease activity in MS patients were confirmed by analysing chemokines receptors on PBL. In contrast, deviation in the Th1/Th2 balance was not observed in NMO patients.</p
The influence of polygenic risk for bipolar disorder on neural activation assessed using fMRI
Genome-wide association studies (GWAS) have demonstrated a significant polygenic contribution to bipolar disorder (BD) where disease risk is determined by the summation of many alleles of small individual magnitude. Modelling polygenic risk scores may be a powerful way of identifying disrupted brain regions whose genetic architecture is related to that of BD. We determined the extent to which common genetic variation underlying risk to BD affected neural activation during an executive processing/language task in individuals at familial risk of BD and healthy controls. Polygenic risk scores were calculated for each individual based on GWAS data from the Psychiatric GWAS Consortium Bipolar Disorder Working Group (PGC-BD) of over 16 000 subjects. The familial group had a significantly higher polygene score than the control group (P=0.04). There were no significant group by polygene interaction effects in terms of association with brain activation. However, we did find that an increasing polygenic risk allele load for BD was associated with increased activation in limbic regions previously implicated in BD, including the anterior cingulate cortex and amygdala, across both groups. The findings suggest that this novel polygenic approach to examine brain-imaging data may be a useful means of identifying genetically mediated traits mechanistically linked to the aetiology of BD
Chronic OVA allergen challenged Siglec-F deficient mice have increased mucus, remodeling, and epithelial Siglec-F ligands which are up-regulated by IL-4 and IL-13
Abstract Background In this study we examined the role of Siglec-F, a receptor highly expressed on eosinophils, in contributing to mucus expression, airway remodeling, and Siglec-F ligand expression utilizing Siglec-F deficient mice exposed to chronic allergen challenge. Methods Wild type (WT) and Siglec-F deficient mice were sensitized and challenged chronically with OVA for one month. Levels of airway inflammation (eosinophils), Siglec-F ligand expresion and remodeling (mucus, fibrosis, smooth muscle thickness, extracellular matrix protein deposition) were assessed in lung sections by image analysis and immunohistology. Airway hyperreactivity to methacholine was assessed in intubated and ventilated mice. Results Siglec-F deficient mice challenged with OVA for one month had significantly increased numbers of BAL and peribronchial eosinophils compared to WT mice which was associated with a significant increase in mucus expression as assessed by the number of periodic acid Schiff positive airway epithelial cells. In addition, OVA challenged Siglec-F deficient mice had significantly increased levels of peribronchial fibrosis (total lung collagen, area of peribronchial trichrome staining), as well as increased numbers of peribronchial TGF-β1+ cells, and increased levels of expression of the extracellular matrix protein fibronectin compared to OVA challenged WT mice. Lung sections immunostained with a Siglec-Fc to detect Siglec-F ligand expression demonstrated higher levels of expression of the Siglec-F ligand in the peribronchial region in OVA challenged Siglec-F deficient mice compared to WT mice. WT and Siglec-F deficient mice challenged intranasally with IL-4 or IL-13 had significantly increased levels of airway epithelial Siglec-F ligand expression, whereas this was not observed in WT or Siglec-F deficient mice challenged with TNF-α. There was a significant increase in the thickness of the peribronchial smooth muscle layer in OVA challenged Siglec-F deficient mice, but this was not associated with significant increased airway hyperreactivity compared to WT mice. Conclusions Overall, this study demonstrates an important role for Siglec-F in modulating levels of chronic eosinophilic airway inflammation, peribronchial fibrosis, thickness of the smooth muscle layer, mucus expression, fibronectin, and levels of peribronchial Siglec-F ligands suggesting that Siglec-F may normally function to limit levels of chronic eosinophilic inflammation and remodeling. In addition, IL-4 and IL-13 are important regulators of Siglec-F ligand expression by airway epithelium
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
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