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

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 family 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 Lyman-α forest may distinguish f(R) models from ΛCDM cosmology at a precision, which is competitive with other probes of f(R) gravity.