Fundamental physics from galaxy shapes

The Lambda Cold Dark Matter model continues to provide a good fit to a wide range of cosmological data, and extensions to the model are almost all disfavoured observationally. This is troubling since neither CDM nor Lambda, together constituting 95% of the cosmic energy budget, are understood. These dark components are invisible, but their presence may be revealed by using galaxy shape alignments to probe weak gravitational lensing by large-scale structure. Weak lensing is quickly maturing into a competitive probe of cosmology, and is expected to become increasingly influential in the next decade with the surveys of Euclid and the Vera C. Rubin Observatory. Tight constraints on dark energy, modified gravity, and neutrino mass are achievable from these large facilities, but with the increase in data volume comes new challenges for dealing with systematics and accurately modelling the signal. In the talk I will discuss the main challenges for weak lensing analyses in the era of Euclid and LSST, including some that have been hitherto overlooked. I will explain the origin of cosmological information from lensing with reference to the current “tensions”, and highlight some of the exciting results that could come out of upcoming surveys such as Euclid.

Speaker will be presenting in-person from the Higgs Centre.