Intensity mapping of post-reionization 21-cm signal and its cross-correlations as a probe of $f(R)$ gravity

TL;DR

This paper explores using 21-cm intensity mapping after reionization as a new way to test $f(R)$ gravity models, showing it can effectively distinguish these models from standard cosmology.

Contribution

It introduces a novel application of 21-cm intensity mapping to constrain $f(R)$ gravity, including cross-correlations with other cosmological probes.

Findings

Radio observations can differentiate $f(R)$ models from $LCDM$ with high precision.

Cross-correlations improve the ability to distinguish gravity models.

The method is competitive with existing $f(R)$ gravity tests.

Abstract

We propose the intensity mapping of the redshifted HI 21-cm signal from the post-reionization epoch as a cosmological probe of $f(R)$ gravity. We consider the Hu-Sawicki class of $f(R)$ gravity models characterized by a single parameter $f_{,R0}$. The $f(R)$ modification to gravity affects the post-reionization $21$-cm power spectrum through the change in the growth rate of density fluctuations. We find that a radio interferometric observation with a SKA1-Mid like radio telescope in both auto-correlation and cross-correlation with galaxy weak-lensing and Ly-$\alpha$ forest may distinguish $f(R)$ models from $LCDM$ cosmology at a precision which is competitive with other probes of $f(R)$ gravity.