535 research outputs found
Neutrino Signatures on the High Transmission Regions of the Lyman-alpha Forest
We quantify the impact of massive neutrinos on the statistics of low density
regions in the intergalactic medium (IGM) as probed by the Lyman-alpha forest
at redshifts z=2.2--4. Based on mock but realistic quasar (QSO) spectra
extracted from hydrodynamic simulations with cold dark matter, baryons and
neutrinos, we find that the probability distribution of weak Lyman-alpha
absorption features, as sampled by Lyman-alpha flux regions at high
transmissivity, is strongly affected by the presence of massive neutrinos. We
show that systematic errors affecting the Lyman-alpha forest reduce but do not
erase the neutrino signal. Using the Fisher matrix formalism, we conclude that
the sum of the neutrino masses can be measured, using the method proposed in
this paper, with a precision smaller than 0.4 eV using a catalog of 200 high
resolution (S/N~100) QSO spectra. This number reduces to 0.27 eV by making use
of reasonable priors in the other parameters that also affect the statistics of
the high transitivity regions of the Lyman-alpha forest. The constraints
obtained with this method can be combined with independent bounds from the CMB,
large scale structures and measurements of the matter power spectrum from the
Lyman-alpha forest to produce tighter upper limits on the sum of the masses of
the neutrinos.Comment: 9 pages, 6 figures. MNRAS Accepte
Constraints on the Proper Motion of the Andromeda Galaxy Based on the Survival of Its Satellite M33
A major uncertainty in the dynamical history of the local group of galaxies
originates from the unknown transverse speed of the Andromeda galaxy (M31)
relative to the Milky Way. We show that the recent VLBA measurement of the
proper motion of Andromeda's satellite, M33, severely constrains the possible
values of M31's proper motion. The condition that M33's stellar disk will not
be tidally disrupted by either M31 or the Milky Way over the past 10 billion
years, favors a proper motion amplitude of 100+-20km/s for M31 with the
quadrant of a negative velocity component along Right Ascension and a positive
component along Declination strongly ruled-out. This inference can be tested by
future astrometric measurements with SIM, GAIA, or the SKA. Our results imply
that the dark halos of Andromeda and the Milky Way will pass through each other
within the next 5-10 billion years.Comment: Accepted for publication in Ap
Inconsistency with De Sitter Spacetime of "Gravitational Pair Production and Black Hole Evaporation"
We study the recent Physical Review Letter [1] which presents a new mechanism
for black hole evaporation through a spatially dependent temperature. This new
temperature is comparable to the Hawking result near the black hole, but is
very small far away, and therefore could be a small correction. Here we apply
the proposed reasoning to the case of de Sitter space, finding that it over
predicts the de Sitter temperature of a minimally coupled scalar by factor of
and therefore cannot be ignored in any limit. This indicates an
inconsistency in the proposed formalism.Comment: 2 pages, 1 figure, in double column forma
Limits on the Position Wander of Sgr A*
We present measurements with the VLBA of the variability in the centroid
position of Sgr A* relative to a background quasar at 7-mm wavelength. We find
an average centroid wander of 71 +/- 45 micro-arcsec for time scales between 50
and 100 min and 113 +/- 50 micro-arcsec for timescales between 100 and 200 min,
with no secular trend. These are sufficient to begin constraining the viability
of the hot-spot model for the radio variability of Sgr A*. It is possible to
rule out hot spots with orbital radii above 15GM_SgrA*/c^2 that contribute more
than 30% of the total 7-mm flux. However, closer or less luminous hot spots
remain unconstrained. Since the fractional variability of Sgr A* during our
observations was ~20% on time scales of hours, the hot-spot model for Sgr A*'s
radio variability remains consistent with these limits. Improved monitoring of
Sgr A*'s centroid position has the potential to place significant constraints
upon the existence and morphology of inhomogeneities in a supermassive black
hole accretion flow.Comment: 14 pages, 3 figures submitted to Ap
Pregnancy as a risk factor for severe influenza infection: an individual participant data meta-analysis
BACKGROUND: WHO identifies pregnant women to be at increased risk for severe outcomes from influenza virus
infections and recommends that they be prioritized for influenza vaccination. The evidence supporting this,
however, is inconsistent. Ecologic studies in particular suggest more severe outcomes from influenza infection
during pregnancy than studies based on individual patient data. Individual studies however may be underpowered
and, as reported in a previous systematic review, confounding factors could not be adjusted for. We therefore
conducted an individual participant data meta-analysis to assess the risk for severe outcomes of influenza infection
in pregnant women while adjusting for other prognostic factors.
METHODS: We contacted authors of studies included in a recently published systematic review. We pooled the
individual participant data of women of reproductive age and laboratory confirmation of influenza virus infection.
We used a generalized linear mixed model and reported odds ratios (OR) and 95% confidence intervals (CI).
RESULTS: A total of 33 datasets with data on 186,656 individuals were available, including 36,498 eligible women of
reproductive age and known pregnancy status. In the multivariable model, pregnancy was associated with a 7
times higher risk of hospital admission (OR 6.80, 95%CI 6.02–7.68), among patients receiving medical care as in- or
outpatients, pregnancy was associated with a lower risk of admission to intensive care units (ICU; OR 0.57, 95%CI
0.48–0.69), and was not significantly associated with death (OR 1.00, 95%CI 0.75–1.34).
CONCLUSIONS: Our study found a higher risk of influenza associated hospitalization among pregnant women as
compared to non-pregnant women. We did not find a higher mortality rate or higher likelihood of ICU admission
among pregnant women who sought medical care. However, this study did not address whether a true
community based cohort of pregnant women is at higher risk of influenza associated complications
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