1508.00895
Performance of internal covariance estimators for cosmic shear correlation functions
Friedrich, Seitz, Eifler, Gruen
Data re-sampling methods such as the delete-one jackknife are a common tool for estimating the covariance of LSS probes. In this paper, investigate the concepts of internal covariance estimation in the context of cosmic shear two-point statistics. Demonstrate how to use log-normal simulations of the convergence field and the corresponding shear field to carry out realistic tests of internal covariance estimators and find that most estimators such as jackknife or sub-sample covariance can reach a satisfactory compromise between bias and variance of the estimated covariance. In a forecast for the complete, 5-year DES survey, show that internally estimated covariance matrices can provide a large fraction of the true uncertainties on cosmological parameters in a 2d cosmic shear analysis. The volume inside contours of constant likelihood in the Omega_m-sigma8 plane as measured with internally estimated covariance matrices is on average >85% of the volume derived from the true covariance matrix. The uncertainty on the parameter combination Sigma8~sigma8Omega_m^0.5 derived from internally estimated covariances is ~90% of the true uncertainty.
1508.01034
Cosmic explotions, life in the universe and the cosmological constant
Piran, Jiminez, Cuesta, Simpson, Verde
Find that Lambda-dominated universes favor the survival of life against GRBs.
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