Orateur
Description
In this talk, I will present constraints on modified gravity using the latest weak lensing data from the Kilo-Degree Survey (KiDS-Legacy), in combination with DESI measurements of baryon acoustic oscillations, eBOSS observations of redshift space distortions, and cosmic microwave background anisotropies from Planck. This analysis explores the Horndeski class of modified gravity models within an effective field theory framework that satisfies stability conditions by construction. We find that cosmic shear provides significant constraints on the Horndeski parameter space, matching or surpassing the CMB contribution, and thus highlighting the role of weak lensing as a powerful probe of gravity on cosmological scales. The results show that although modified gravity provides a slightly improved fit to the data, a model comparison indicates only a weak preference over $\Lambda$CDM, while key observables, such as the structure growth parameter S_8, remain consistent with $\Lambda$CDM constraints.