41 research outputs found
The effect of neutrinos on the matter distribution as probed by the Intergalactic Medium
We present a suite of full hydrodynamical cosmological simulations that
quantitatively address the impact of neutrinos on the (mildly non-linear)
spatial distribution of matter and in particular on the neutral hydrogen
distribution in the Intergalactic Medium (IGM), which is responsible for the
intervening Lyman-alpha absorption in quasar spectra. The free-streaming of
neutrinos results in a (non-linear) scale-dependent suppression of power
spectrum of the total matter distribution at scales probed by Lyman-alpha
forest data which is larger than the linear theory prediction by about 25% and
strongly redshift dependent. By extracting a set of realistic mock quasar
spectra, we quantify the effect of neutrinos on the flux probability
distribution function and flux power spectrum. The differences in the matter
power spectra translate into a ~2.5% (5%) difference in the flux power spectrum
for neutrino masses with Sigma m_{\nu} = 0.3 eV (0.6 eV). This rather small
effect is difficult to detect from present Lyman-alpha forest data and nearly
perfectly degenerate with the overall amplitude of the matter power spectrum as
characterised by sigma_8. If the results of the numerical simulations are
normalized to have the same sigma_8 in the initial conditions, then neutrinos
produce a smaller suppression in the flux power of about 3% (5%) for Sigma
m_{\nu} = 0.6 eV (2
sigma C.L.), comparable to constraints obtained from the cosmic microwave
background data or other large scale structure probes.Comment: 38 pages, 21 figures. One section and references added. JCAP in pres
Semi-empirical catalog of early-type galaxy-halo systems: dark matter density profiles, halo contraction and dark matter annihilation strength
With SDSS galaxy data and halo data from up-to-date N-body simulations we
construct a semi-empirical catalog (SEC) of early-type systems by making a
self-consistent bivariate statistical match of stellar mass (M_star) and
velocity dispersion (sigma) with halo virial mass (M_vir). We then assign
stellar mass profile and velocity dispersion profile parameters to each system
in the SEC using their observed correlations with M_star and sigma.
Simultaneously, we solve for dark matter density profile of each halo using the
spherical Jeans equation. The resulting dark matter density profiles deviate in
general from the dissipationless profile of NFW or Einasto and their mean inner
density slope and concentration vary systematically with M_vir. Statistical
tests of the distribution of profiles at fixed M_vir rule out the null
hypothesis that it follows the distribution predicted by N-body simulations for
M_vir ~< 10^{13.5-14.5} M_solar. These dark matter profiles imply that dark
matter density is, on average, enhanced significantly in the inner region of
halos with M_vir ~< 10^{13.5-14.5} M_solar supporting halo contraction. The
main characteristics of halo contraction are: (1) the mean dark matter density
within the effective radius has increased by a factor varying systematically up
to ~ 3-4 at M_vir = 10^{12} M_solar, and (2) the inner density slope has a mean
of ~ 1.3 with rho(r) ~ r^{-alpha} and a halo-to-halo rms scatter of
rms(alpha) ~ 0.4-0.5 for 10^{12} M_solar ~< M_vir ~< 10^{13-14} M_solar steeper
than the NFW profile (alpha=1). Based on our results we predict that halos of
nearby elliptical and lenticular galaxies can, in principle, be promising
targets for gamma-ray emission from dark matter annihilation.Comment: 43 pages, 20 figures, JCAP, revised and accepted versio
Constraining primordial non-Gaussianity with cosmological weak lensing: shear and flexion
We examine the cosmological constraining power of future large-scale weak
lensing surveys on the model of \emph{Euclid}, with particular reference to
primordial non-Gaussianity. Our analysis considers several different estimators
of the projected matter power spectrum, based on both shear and flexion, for
which we review the covariances and Fisher matrices. The bounds provided by
cosmic shear alone for the local bispectrum shape, marginalized over
, are at the level of . We consider
three additional bispectrum shapes, for which the cosmic shear constraints
range from (equilateral shape) up to (orthogonal shape). The competitiveness of cosmic
flexion constraints against cosmic shear ones depends on the galaxy intrinsic
flexion noise, that is still virtually unconstrained. Adopting the very high
value that has been occasionally used in the literature results in the flexion
contribution being basically negligible with respect to the shear one, and for
realistic configurations the former does not improve significantly the
constraining power of the latter. Since the flexion noise decreases with
decreasing scale, by extending the analysis up to
cosmic flexion, while being still subdominant, improves the shear constraints
by when added. However on such small scales the highly non-linear
clustering of matter and the impact of baryonic physics make any error
estimation uncertain. By considering lower, and possibly more realistic, values
of the flexion intrinsic shape noise results in flexion constraining power
being a factor of better than that of shear, and the bounds on
and being improved by a factor of upon
their combination. (abridged)Comment: 30 pages, 4 figures, 4 tables. To appear on JCA
Weak lensing, dark matter and dark energy
Weak gravitational lensing is rapidly becoming one of the principal probes of
dark matter and dark energy in the universe. In this brief review we outline
how weak lensing helps determine the structure of dark matter halos, measure
the expansion rate of the universe, and distinguish between modified gravity
and dark energy explanations for the acceleration of the universe. We also
discuss requirements on the control of systematic errors so that the
systematics do not appreciably degrade the power of weak lensing as a
cosmological probe.Comment: Invited review article for the GRG special issue on gravitational
lensing (P. Jetzer, Y. Mellier and V. Perlick Eds.). V3: subsection on
three-point function and some references added. Matches the published versio
General Requirements on Matter Power Spectrum Predictions for Cosmology with Weak Lensing Tomography
Forthcoming projects such as DES, LSST, WFIRST, and Euclid aim to measure
weak lensing shear correlations with unprecedented precision, constraining the
dark energy equation of state at the percent level. Reliance on
photometrically-determined redshifts constitutes a major source of uncertainty
for these surveys. Additionally, interpreting the weak lensing signal requires
a detailed understanding of the nonlinear physics of gravitational collapse. We
present a new analysis of the stringent calibration requirements for weak
lensing analyses of future imaging surveys that addresses both photo-z
uncertainty and errors in the calibration of the matter power spectrum. We find
that when photo-z uncertainty is taken into account the requirements on the
level of precision in the prediction for the matter power spectrum are more
stringent than previously thought. Including degree-scale galaxy clustering
statistics in a joint analysis with weak lensing not only strengthens the
survey's constraining power by ~20%, but can also have a profound impact on the
calibration demands, decreasing the degradation in dark energy constraints with
matter power spectrum uncertainty by a factor of 2-5. Similarly, using galaxy
clustering information significantly relaxes the demands on photo-z
calibration. We compare these calibration requirements to the contemporary
state-of-the-art in photometric redshift estimation and predictions of the
power spectrum and suggest strategies to utilize forthcoming data optimally.Comment: 3 new figures; new section added on multipole-dependence of
calibration requirements; references added; version accepted by JCA
Enid Blyton and the mystery of children's literature
SIGLEAvailable from British Library Document Supply Centre-DSC:DXN011280 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
British Society of Gastroenterology guidelines on the management of functional dyspepsia
Functional dyspepsia (FD) is a common disorder of gut–brain interaction, affecting approximately 7% of individuals in the community, with most patients managed in primary care. The last British Society of Gastroenterology (BSG) guideline for the management of dyspepsia was published in 1996. In the interim, substantial advances have been made in understanding the complex pathophysiology of FD, and there has been a considerable amount of new evidence published concerning its diagnosis and classification, with the advent of the Rome IV criteria, and management. The primary aim of this guideline, commissioned by the BSG, is to review and summarise the current evidence to inform and guide clinical practice, by providing a practical framework for evidence-based diagnosis and treatment of patients. The approach to investigating the patient presenting with dyspepsia is discussed, and efficacy of drugs in FD summarised based on evidence derived from a comprehensive search of the medical literature, which was used to inform an update of a series of pairwise and network meta-analyses. Specific recommendations have been made according to the Grading of Recommendations Assessment, Development and Evaluation system. These provide both the strength of the recommendations and the overall quality of evidence. Finally, in this guideline, we consider novel treatments that are in development, as well as highlighting areas of unmet need and priorities for future research