# The Hubble constant tension with next-generation galaxy surveys

## TL;DR

Next-generation galaxy surveys like Euclid and SKA can measure the Hubble parameter across a wide redshift range with high precision, potentially resolving the current tension in Hubble constant measurements by providing independent constraints.

## Contribution

This paper demonstrates how upcoming spectroscopic galaxy surveys can precisely measure H(z) and extrapolate to H0, offering a new method to address the Hubble tension.

## Key findings

- Euclid-like surveys can achieve ~3% precision on H0
- SKA-like surveys can reach ~2% precision on H0
- Combining multiple surveys can improve precision to ~1% and resolve the tension

## Abstract

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, $H_0$, show a significant tension ($\sim 4-6\sigma$) 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 $H_0$ using a non-parametric regression. To this end we deploy Gaussian processes and we find that Euclid-like surveys can reach $\sim$3\% precision on $H_0$, with SKA-like intensity mapping surveys reaching $\sim$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-Universe measurements at a $\sim$5$\sigma$ level.