Date: **May 3rd 2018
**

Speaker:** Alessio Spurio Mancini
**

Title: **Weak gravitational lensing as a (3D) probe of gravity
**

**Abstract**

Cosmic shear, the weak gravitational lensing effect 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 ΛCDM with one scalar degree of freedom

in addition to the metric, which are still in agreement with current

observations.

In this talk I will discuss some aspects concerning the constraining

power of current and future cosmic shear datasets on this broad class of

theories. I will compare in particular 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. Due to its increased

amount of redshift information, a future 3D analysis can constrain both

standard gravity and Horndeski theories better than a tomographic one,

in particular with a decrease in the errors on the Horndeski parameters

of the order of 20%.