61 research outputs found
DEMNUni: Massive neutrinos and the bispectrum of large scale structures
The main effect of massive neutrinos on the large-scale structure consists in
a few percent suppression of matter perturbations on all scales below their
free-streaming scale. Such effect is of particular importance as it allows to
constraint the value of the sum of neutrino masses from measurements of the
galaxy power spectrum. In this work, we present the first measurements of the
next higher-order correlation function, the bispectrum, from N-body simulations
that include massive neutrinos as particles. This is the simplest statistics
characterising the non-Gaussian properties of the matter and dark matter halos
distributions. We investigate, in the first place, the suppression due to
massive neutrinos on the matter bispectrum, comparing our measurements with the
simplest perturbation theory predictions, finding the approximation of
neutrinos contributing at quadratic order in perturbation theory to provide a
good fit to the measurements in the simulations. On the other hand, as
expected, a linear approximation for neutrino perturbations would lead to
O() errors on the total matter bispectrum at large scales. We then
attempt an extension of previous results on the universality of linear halo
bias in neutrino cosmologies, to non-linear and non-local corrections finding
consistent results with the power spectrum analysis.Comment: 22 pages, 11 figure
Optimal Redshift Weighting For Redshift Space Distortions
The low statistical errors on cosmological parameters promised by future
galaxy surveys will only be realised with the development of new, fast,
analysis methods that reduce potential systematic problems to low levels. We
present an efficient method for measuring the evolution of the growth of
structure using Redshift Space Distortions (RSD), that removes the need to make
measurements in redshift shells. We provide sets of galaxy-weights that cover a
wide range in redshift, but are optimised to provide differential information
about cosmological evolution. These are derived to optimally measure the
coefficients of a parameterisation of the redshift-dependent matter density,
which provides a framework to measure deviations from the concordance
CDM cosmology, allowing for deviations in both geometric and/or
growth. We test the robustness of the weights by comparing with alternative
schemes and investigate the impact of galaxy bias. We extend the results to
measure the combined anisotropic Baryon Acoustic Oscillation (BAO) and RSD
signals.Comment: 10 pages, 5 figures, submitted to MNRA
Testing modified gravity scenarios with direct peculiar velocities
The theoretical basis of dark energy remains unknown and could signify a need
to modify the laws of gravity on cosmological scales. In this study we
investigate how the clustering and motions of galaxies can be used as probes of
modified gravity theories, using galaxy and direct peculiar velocity auto- and
cross-correlation functions. We measure and fit these correlation functions in
simulations of CDM, DGP, and cosmologies and, by extracting the
characteristic parameters of each model, we show that these theories can be
distinguished from General Relativity using these measurements. We present
forecasts showing that with sufficiently large data samples, this analysis
technique is a competitive probe that can help place limits on allowed
deviations from GR. For example, a peculiar velocity survey reaching to
with distance accuracy would constrain model parameters to 3-
confidence limits for nDGP, assuming a fiducial GR model.Comment: 13 pages, 12 figures, 3 tables, accepted for publication in MNRA
Cross-correlating radial peculiar velocities and CMB lensing convergence
We study, for the first time, the cross correlation between the angular
distribution of radial peculiar velocities (PV) and the lensing convergence of
cosmic microwave background (CMB) photons. We derive theoretical expectations
for the signal and its covariance and assess its detectability with existing
and forthcoming surveys. We find that such cross-correlations are expected to
improve constraints on different gravitational models by partially breaking
degeneracies with the matter density. We identify in the distance-scaling
dispersion of the peculiar velocities the most relevant source of noise in the
cross correlation. For this reason, we also study how the above picture changes
assuming a redshift-independent scatter for the PV, obtained for example using
a reconstruction technique. Our results show that the cross correlation might
be detected in the near future combining PV measurements from DESI and the
convergence map from CMB-S4. Using realistic direct PV measurements we predict
a cumulative signal-to-noise ratio of approximately using data on
angular scales . For an idealized reconstructed peculiar
velocity map extending up to redshift and a smoothing scale of Mpc
we predict a cumulative signal-to-noise ratio of approximately from angular scales . We conclude that currently
reconstructed peculiar velocities have more constraining power than directly
observed ones, even though they are more cosmological-model dependent.Comment: 20 pages plus references, 5 figures. Comments are welcom
Redshift-weighted constraints on primordial non-Gaussianity from the clustering of the eBOSS DR14 quasars in Fourier space
We present constraints on local primordial non-Gaussianity (PNG),
parametrized through , using the Sloan Digital Sky Survey
IV extended Baryon Oscillation Spectroscopic Survey Data Release 14 quasar
sample. We measure and analyze the anisotropic clustering of the quasars in
Fourier space, testing for the scale-dependent bias introduced by primordial
non-Gaussianity on large scales. We derive and employ a power spectrum
estimator using optimal weights that account for the redshift evolution of the
PNG signal. We find constraints of at 95%
confidence level. These are amont the tightest constraints from Large Scale
Structure (LSS) data. Our redshift weighting improves the error bar by 15% in
comparison to the unweighted case. If quasars have lower response to PNG, the
constraint degrades to , with a 40% improvement
over the standard approach. We forecast that the full eBOSS dataset could reach
using optimal methods and full
range of scales.Comment: 28 pages, 12 figures. Comments welcome
The extended Baryon Oscillation Spectroscopic Survey (eBOSS):testing a new approach to measure the evolution of the structure growth
International audienceThe extended Baryon Oscillation Spectroscopic Survey (eBOSS) is one of the first of a new generation of galaxy redshift surveys that will cover a large range in redshift with sufficient resolution to measure the baryon acoustic oscillations signal. For surveys covering a large redshift range we can no longer ignore cosmological evolution, meaning that either the redshift shells analysed have to be significantly narrower than the survey, or we have to allow for the averaging over evolving quantities. Both of these have the potential to remove signal: analysing small volumes increases the size of the Fourier window function, reducing the large-scale information, while averaging over evolving quantities can, if not performed carefully, remove differential information. It will be important to measure cosmological evolution from these surveys to explore and discriminate between models. We apply a method to optimally extract this differential information to mock catalogues designed to mimic the eBOSS quasar sample. By applying a set of weights to extract redshift-space distortion measurements as a function of redshift, we demonstrate an analysis that does not invoke the problems discussed above. We show that our estimator gives unbiased constraints
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