Day 1009

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1511.05969
Parameter inference with estimated covariance matrices
Sellentin, Heavens

When inferring parameters from a Gaussian-distributed data set by computing a likelihood, a covariance matrix is needed that describes the data errors and their correlations.  If the covariance matrix is not known a priori, it may be estimated and thereby becomes a random object with some intrinsic uncertainty itself.  Show how to infer parameters in the presence of such an estimated covariance matrix, by marginalizing over the true covariance matrix, conditioned on its estimated value.  This leads to a likelihood function that is no longer Gaussian, but rather an adapted version of a multivariate t-distribution, which has the same numerical complexity as the multivariate Gaussian.  As expected, marginalization over the true covariance matrix improves inference when compared with Hartlap+'s method, which uses an unbiased estimate of the inverse covariance matrix but still assumes that the likelihood is Gaussian.


1511.05983
Neutrino mass limits: robust information from the power spectrum of galaxy surveys
Cuesta, Niro, Verde

Present cosmo upper limits on the sum of active neutrino masses using large-scale power spectrum data from the WiggleZ DarkEnergy Survey and from SDSS-DR7 sample of LRGs.  Combining measurements on the CMB temperature and polarization anisotropies by the Planck satellite together with WiggleZ power spectrum results in a neutrino mass bound of 0.43 eV at 95% C.L., while replacing WiggleZ by the SDSS-DR7 LRG PS, the 95% C.L. bound on the sum of neutrino masses improves to 0.17 eV.  Adding BAO distance scale measurements, the neutrino mass upper limits greatly improve, since BAO data break degeneracies in parameter space.  Within a LCDM model, find an upper limit of 0.11 eV (0.15 eV) at 95% C.L., when using SDSS-DR7 LRG (WiggleZ) together with BAO and Planck.  The addition of BAO data makes the neutrino mass upper limit robust, showing only a weak dependence on the PS used.  Also quantify the dependence of neutrino mass limit reported here on the CMB lensing information.  The tighter upper limit (0.11 eV) obtained with SDSS-DR7 LRG is very close to that recently obtained using Lyman-alpha clustering data, yet uses a completely different probe and redshift range, further supporting the robustness of the constraint.  This constraint puts under some pressure the inverted mass hierarchy and favors the normal hierarchy.


1511.05994
Gravitational-wave cosmology across 29 decades in frequency
Lanky et al

Quantum fluctuations of the gravitational field in the early Universe, amplified by inflation, produce a primordial gravitational-wave background across a broad frequency band.  Derive constraints on the spectrum of this gravitational radiation, and hence on theories of the early Universe, by combining experiments that cover 29 orders of magnitude in frequency.  These include Planck observations of cosmic microwave background temperature and polarization power spectra and lensing, together with BAO and BBN measurements, as well as new pulsar timing array and ground-based interferometer limits.  While individual experiment constrain the gravitational-wave energy density in specific frequency bands, the combination of experiments allows to constrain cosmological parameters, including the inflationary spectral index, n_t, and the tensor-to-scalar ratio, r.  Results from individual experiments include the most stringent nanohertz limit of the primordial background to date from the Parkes Pulsar Timing Array, Omega_gw(f) < 2.3e-10.  Observations of the CMB alone limit the gravitational-wave spectral index at 95% confidence to n_t<~5 for a r=0.11.  However, the combination of all the above experiments limits n_t<0.36.  Further Advanced LIGO observations are expected to further constraint n_t<0.34 by 2020.  When CMB experiments detect a non-zero r, the results will imply even more stringent constraints on n_t and hence theories of the early Universe.


1511.06741
The sparkling Universe: a scenario for cosmic void motions
Ceccarelli, et al

Perform a statistical study of the global motion of cosmic voids using both a numerical sim and observational data.  Analyze their relation to LS mass flows and the physical effects that drive those motions.  Analyze the bulk motions of voids, defined by the mean velocity of haloes in the surrounding shells in the numerical simulation, and by galaxies in SDSS DR7.  Find void mean bulk velocities close to 400 km/s, comparable to those of haloes (~500-600 km/s), depending on void size and the LS environment.  Statistically, small voids move faster than large ones, and voids in relatively higher density environments have higher bulk velocities than those placed in large underdense regions.  Analyze the mean mass density around voids finding LS over densities (under densities) along (opposite to) the void motion direction, suggesting that void motions respond to a pull-push mechanism.   This contrasts with massive cluster motions who are mainly governed by the pull of the LS overdense regions.  The analysis of void pairwise velocities shows how their relative motions are generated by LS density fluctuations.  In agreement with linear theory, voids embedded in low (high) density regions mutually recede (attract) each other, providing the general mechanism to understand the bimodal behavior of void motions.  In order to compare the theoretical results and the observations, infer void motions in the SDSS using near theory, finding that the estimated observational void motions are in statistical agreement with the results of the simulation.  Regarding LS flows, results suggest a scenario of galaxies and galaxy systems flowing away from void centers with the additional, and more relevant, contribution of the void bulk motion to the total velocity.