Day 719

Monday.

1408.1744
The impact of super-survey modes on cosmological constraints from cosmic shear fields
Carron, Szapudi

Owing to the mass-sheet degeneracy, cosmic shear maps do not probe directly the Fourier modes of the underlying mass distribution on scales comparable to the survey size and larger. To assess the corresponding effect on attainable cosmological parameter constraints, quantify the information on surper-survey modes in a lognormal model and, when interpreted as nuisance parameters, their degeneracies to cosmological parameters.  The analytical and numerical calculations clarify the central role of super-sample covariance (SSC) in shaping the statistical power of cosmological observables.  Reconstructing the background modes from their non-Gaussian statistical dependence to small scales modes yields the renormalized convergence.  The diagonalizes the spectrum covariance matrix, and the information content of the corresponding PS is increased by a factor of 2 over standard methods.  Unfortunately, careful calculation of the Cramer-Rao bound shows that the information recovery can never be made complete.  Any observable built from shear fields, including optimal sufficient statistics, are subject to severe information loss, typically 80 to 90% below ell~3000 for generic cosmological parameters.  The lost information can only be recovered from additional, non-shear based data.  Predictions hold just as well for tomographic analysis, and/or full sky surveys.

1408.1872
Probing spatial homogeneity with LTB models: a detailed discussion
Redlich, ... Bartelmann, et al

To address the question of any statistical evidence for deviations from spatial homogeneity on large scales, developed a flexible framework based on spherically symmetric, but radial inhomogeneous LTB models with synchronous Big Bang.  A Monte Carlo Technique in combination with recent observational data was used to systematically vary the shape of the profiles.  (i) Reconsider giant LTB voids without DE to investigate whether extremely fine-tuned mass profiles can reconcile models with current data.  It can, but requires a Hubble rate which is too low compared to observations.  (ii) explain why it seems natural to extend the framework by a non-zero cosmological constant, which then allows general tests of the cosmological principle.  These extended models facilitate explorating whether fluctuations in the local matter density profile might potentially alleviate the tension between local and global measurements of the Hubble rate, as derived from Cepheid-calibrated type Ia SNe and CMB experiments, respectively.  Show that current data provide no evidence for deviations from spatial homogeneity on large scales.  More accurate constraints are required to ultimately confirm the validity of the cosmological principle, however.