Cosmological forecast of the 21-cm power spectrum using the halo model of reionization

TL;DR

This paper introduces the halo model of reionization (HMreio), an analytical tool for forecasting the 21-cm power spectrum, enabling efficient cosmological parameter estimation and testing tensions like H0 and S8 with SKA data.

Contribution

The paper presents HMreio, a new analytical model validated against semi-numerical simulations, for fast and accurate cosmological forecasts using 21-cm observations.

Findings

HMreio agrees well with 21cmFAST for k<1 h/Mpc.

Forecasts show potential to resolve H0 and S8 tensions.

Neutrino mass hierarchy can be constrained to 90% confidence.

Abstract

The 21-cm power spectrum of reionization is a promising probe for cosmology and fundamental physics. Exploiting this new observable, however, requires fast predictors capable of efficiently scanning the very large parameter space of cosmological and astrophysical uncertainties. In this paper, we introduce the halo model of reionization (HMreio), a new analytical tool that combines the halo model of the cosmic dawn with the excursion-set bubble model for reionization, assuming an empirical correction factor to deal with overlapping ionization bubbles. First, HMreio is validated against results from the well-known semi-numerical code 21cmFAST, showing a good overall agreement for wave-modes of $k\lesssim 1$ h/Mpc. Based on this result, we perform a Monte-Carlo Markov-Chain (MCMC) forecast analysis assuming mock data from 1000-hour observations with the low-frequency part of the Square Kilometre Array (SKA) observatory. We simultaneously vary the six standard cosmological parameters together with seven astrophysical nuisance parameters quantifying the abundance and spectral properties of sources. Depending on the assumed theory error, we find very competitive constraints on cosmological parameters. In particular, it will be possible to conclusively test current cosmological tensions related to the Hubble parameter ($H_0$-tension) and the matter clustering amplitude ($S_8$-tension). Furthermore, the sum of the neutrino masses can be strongly constrained, making it possible to determine the neutrino mass hierarchy at the $\sim 90$ percent confidence level. However, these goals can only be achieved if the current modelling uncertainties are substantially reduced to below $\sim 3$ percent.