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Journal-club Univers / Journal-club Universe

« Weak gravitational lensing as a (3D) probe of gravity »

Alessio Spurio Mancini
Institut für Theoretische Physik, Ruprecht-Karls-Universität Heidelberg (Heidelberg, Allemagne)

Cosmic shear, the weak gravitational lensing caused by the large-scale structure, is one of the primary probes to test gravity on cosmological scales with current and future surveys. In particular, cosmic shear is sensitive to both standard GR cosmological parameters and those that describe modified theories of gravity, such as those belonging to the Horndeski class. These models include the majority of universally coupled extensions to ?CDM with one scalar degree of freedom in addition to the metric, which are still in agreement with current observations. There are two main techniques to analyse a cosmic shear survey; a tomographic method, where correlations between the lensing signal in different redshift bins are used to recover redshift information, and a 3D approach, where the full redshift information is carried through the entire analysis. In this talk, I will start presenting the first constraints on Horndeski gravity obtained from the analysis of tomographic cosmic shear data from the KiDS survey, in cross-correlation with the galaxy- matter cross-correlation function and the two-point clustering auto-correlation function of galaxies from the GAMA survey. I will then compare the constraining power of the tomographic and the 3D approach on Horndeski gravity and on standard cosmological parameters, presenting Fisher matrix forecasts for future surveys like Euclid. Due to its increased amount of redshift information, a future 3D analysis has the power to constrain both standard gravity and Horndeski theories better than a tomographic one, producing in particular a decrease in the errors on the Horndeski parameters of the order of 20 - 30% and an error on the sum of the neutrino masses three times smaller than in tomography. Finally, I will show how to use the 3D cosmic shear covariance matrices to generate in spherical coordinates spin-2 Gaussian random fields. This opens up the possibility of a future Bayesian Hierarchical Model for 3D cosmic shear power spectra estimation, as a principled approach to cosmological inference, correctly and completely propagating different sources of systematics.
vendredi 4 mai 2018 - 14:00
Salle 281, Institut d'Astrophysique
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