The Hubble constant tension with next-generation galaxy surveys

The rate at which the universe is expanding today is a fundamental parameter in cosmology which governs our understanding of structure formation and dark energy. However, current measurements of the Hubble constant, H₀, show a significant tension (∼ 4 − 6σ) between early- and late-Universe observations. There are ongoing efforts to check the diverse observational results and also to investigate possible theoretical ways to resolve the tension – which could point to radical extensions of the standard model. Here we demonstrate the potential of next-generation spectroscopic galaxy surveys to shed light on the Hubble constant tension. Surveys such as those with Euclid and the Square Kilometre Array (SKA) are expected to reach sub-percent precision on Baryon Acoustic Oscillation (BAO) measurements of the Hubble parameter, with a combined redshift coverage of 0.1 < z < 3. This wide redshift range, together with the high precision and low level of systematics in BAO measurements, mean that these surveys will provide independent and tight constraints on H(z). These H(z) measurements can be extrapolated to z = 0 to provide constraints on H₀ using a non-parametric regression. To this end we deploy Gaussian processes and we find that Euclid-like surveys can reach ∼3% precision on H₀, with SKA-like intensity mapping surveys reaching ∼2%. When we combine the low-redshift SKA-like Band 2 survey with either its high-redshift Band 1 counterpart, or with the non-overlapping Euclid-like survey, the precision is predicted to be close to 1% with 40 H(z) data points. This would be sufficient to rule out the current early- or late-Universemeasurements at a ∼5σ level.