Testing the Standard Cosmological Model: Late-Universe Constraints on the Clustering of Matter with Early-Universe Priors

The Standard Cosmological Model (ΛCDM) successfully predicts a series of observations, but it has tensions when the model parameters are constrained using different observational probes. The s8 tension is a disagreement in the level of clustering of matter ("clumpiness" of the universe) between early-time, Cosmic Microwave Background (CMB) and late-time galactic surveys; the latter measure less clustering today than suggested by CMB surveys at the 2-3σ level, making it a significant puzzle in cosmology. Here, this tension is addressed using the final data release of the Dark Energy Survey. Bayesian parameter inference with CosmoSIS is employed but enforcing informative CMB priors. We ask: does feeding early-universe informed priors in our inference with late universe data worsen or alleviate the s8 tension? The answer will help discern whether the tension originates from systematics in the data or if physics beyond ΛCDM is needed.