Sacha Guerrini

Weak gravitational lensing refers to the slight distortion of galaxy shapes as light travels across the Universe's large-scale structures. Sensitive to the projected mass density, cosmic shear is a powerful probe to constrain the growth of structures and the dynamics of dark energy. The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is a photometric survey covering 4800 square degrees in the u, g, r, i and z bands, with the Canada-France Imaging Survey (CFIS) component providing deep u- and r-band imaging. UNIONS is the last so-called "Stage III" survey before the avenue of LSST, Euclid, Roman and others. Those new generation surveys will push the statistical precision to an unprecedented level, and will require exquisite control of systematic uncertainties. In this talk, I will describe my contribution to UNIONS, from the data processing to the cosmological analysis. I will present the lessons learned from processing the CFIS ground-based data emphasising validation and mitigation of PSF systematics. Finally, I will introduce efforts invested in forward modelling weak lensing survey for Simulation-Based Inference, a promising Bayesian inference technique to extract more cosmological information from the data.