COLIBRI · Cosmic nOn-Linearities: Impact of BaRyons on cosmological Inference with modern galaxy surveys

Cosmology is entering a new era with revolutionary surveys aimed notably at mapping dark matter and constraining the nature of dark energy. However, the observables are always related to ""visible"" matter (baryons) which is a biased tracer of dark matter. Baryons do not passively follow the assembly of dark matter structures, but they also feedback on the distribution of dark matter, and therefore impact significatively the estimators probing cosmology. If these effects are not precisely taken into account, they induce biases and could potentially engender apparent tensions, some of which are already observed, between the various cosmological surveys and probes. The COLIBRI project proposes to robustly keep under control the effect of baryons on the joint analysis of galaxy lensing and clustering data through i) new theoretical frameworks to capture efficiently the cosmological information content on mildly non-linear scales affected by baryons and ii) novel hydrodynamical simulations accurately resolving baryonic physics inside unprecedentedly large volumes, enabled by innovative simulation techniques and the evolution of computing resources in Europe in the exascale era. These simulations and theoretical schemes will then allow for a robust characterisation of baryons on cosmological scales, in order to interpret current and future large galaxy surveys with enough precision and accuracy. This effort is crucial to make the most out of the rich datasets that will be observed, with in particular the upcoming Euclid’s data releases.""