22 research outputs found
Nonlinear Stochastic Biasing of Peaks and Halos: Scale-Dependence, Time-Evolution, and Redshift-Space Distortion from Cosmological N-body Simulations
We quantify the degree of nonlinearity and stochasticity of the clustering of
biased objects, using cosmological N-body simulations. Adopting the peaks and
the halos as representative biasing models, we focus on the two-point
correlation of the biased objects, dark matter and their cross-correlation.
Especially, we take account of the effect of redshift-space distortion and
attempt to clarify the scale-dependence and the time-dependence by analyzing
the biasing factor and the cross-correlation factor. On small scales,
stochasticity and nonlinearity become appreciable and strongly
object-dependent, especially in redshift space due to the pair-wise velocity
dispersion of the biased objects. Nevertheless, an approximation of
deterministic linear biasing works reasonably well even in the quasi-linear regime
Mpc, and linear redshift-space distortion explains the clustering amplitudes in
redshift space in this regime.Comment: 17 pages, 9 figures, accepted for publication in PAS
Measuring our universe from galaxy redshift surveys
Galaxy redshift surveys have achieved significant progress over the last
couple of decades. Those surveys tell us in the most straightforward way what
our local universe looks like. While the galaxy distribution traces the bright
side of the universe, detailed quantitative analyses of the data have even
revealed the dark side of the universe dominated by non-baryonic dark matter as
well as more mysterious dark energy (or Einstein's cosmological constant). We
describe several methodologies of using galaxy redshift surveys as cosmological
probes, and then summarize the recent results from the existing surveys.
Finally we present our views on the future of redshift surveys in the era of
Precision Cosmology.Comment: 82 pages, 31 figures, invited review article published in Living
Reviews in Relativity, http://www.livingreviews.org/lrr-2004-
Anti-SARS-CoV-2 antibodies in the CSF, blood-brain barrier dysfunction, and neurological outcome: Studies in 8 stuporous and comatose patients
OBJECTIVE: To investigate the pathophysiologic mechanism of encephalopathy and prolonged comatose or stuporous state in severally ill patients with coronavirus disease 2019 (COVID-19). METHODS: Eight COVID-19 patients with signs of encephalopathy were tested for antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the serum and CSF using a Food and Drug Administration-approved and independently validated ELISA. Blood-brain barrier (BBB) integrity and immunoglobulin G (IgG) intrathecal synthesis were further tested using albumin and IgG indices. The CSF was also tested for autoimmune encephalitis antibodies and 14-3-3, a marker of ongoing neurodegeneration. RESULTS: All patients had anti-SARS-CoV-2 antibodies in their CSF, and 4 of 8 patients had high titers, comparable to high serum values. One patient had anti-SARS-CoV-2 IgG intrathecal synthesis, and 3 others had disruption of the blood-brain barrier. The CSF in 4 patients was positive for 14-3-3-protein suggesting ongoing neurodegeneration. In all patients, the CSF was negative for autoimmune encephalitis antibodies and SARS-CoV-2 by PCR. None of the patients, apart from persistent encephalopathic signs, had any focal neurologic signs or history or specific neurologic disease. CONCLUSIONS: High-titer anti-SARS-CoV-2 antibodies were detected in the CSF of comatose or encephalopathic patients demonstrating intrathecal IgG synthesis or BBB disruption. A disrupted BBB may facilitate the entry of cytokines and inflammatory mediators into the CNS enhancing neuroinflammation and neurodegeneration. The observations highlight the need for prospective CSF studies to determine the pathogenic role of anti-SARS-CoV-2 antibodies and identify early therapeutic interventions. Copyright © 2020 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology
Modelling non-linear effects of dark energy
We investigate the capabilities of perturbation theory in capturing
non-linear effects of dark energy. We test constant and evolving
models, as well as models involving momentum exchange between dark energy and
dark matter. Specifically, we compare perturbative predictions at 1-loop level
against N-body results for four non-standard equations of state as well as
varying degrees of momentum exchange between dark energy and dark matter. The
interaction is modelled phenomenologically using a time dependent drag term in
the Euler equation. We make comparisons at the level of the matter power
spectrum and the redshift space monopole and quadrupole. The multipoles are
modelled using the Taruya, Nishimichi and Saito (TNS) redshift space spectrum.
We find perturbation theory does very well in capturing non-linear effects
coming from dark sector interaction. We isolate and quantify the 1-loop
contribution coming from the interaction and from the non-standard equation of
state. We find the interaction parameter amplifies scale dependent
signatures in the range of scales considered. Non-standard equations of state
also give scale dependent signatures within this same regime. In redshift space
the match with N-body is improved at smaller scales by the addition of the TNS
free parameter . To quantify the importance of modelling the
interaction, we create mock data sets for varying values of using
perturbation theory. This data is given errors typical of Stage IV surveys. We
then perform a likelihood analysis using the first two multipoles on these sets
and a modelling, ignoring the interaction. We find the fiducial growth
parameter is generally recovered even for very large values of both
at and . The modelling is most biased in its estimation of
for the phantom case.Comment: 22 pages, 15 figures. Added text elucidating method and results.
Included new Fig. 12. Accepted for publication in JCA