Effective bias expansion for 21-cm cosmology in redshift space

A near-future detection of the 21-cm signal from the epoch of reionization will provide unique opportunities to probe the underlying cosmology, provided that such cosmological information can be extracted with precision. To this end, we further develop effective field theory (EFT) inspired techniques for the 21-cm brightness temperature field during the epoch of reionization, incorporating renormalized bias and a treatment of redshift space distortions. Notably, we confirm that in redshift space, measures of the 21-cm brightness, e.g., the power spectrum, should have irreducible contributions that lack a bias coefficient and therefore contain direct, astrophysics-free information about the cosmological density field; in this work, we study this effect beyond linear order. To validate our theoretical treatment, we fit the predicted EFT Fourier-space shapes to the THESAN suite of hydrodynamical simulations of reionization at the field level, where the considerable number of modes prevents overfitting. We find agreement at the level of a few percent between the 21-cm power spectrum from the EFT fits and simulations over the wave number range k less than or similar to 0.8 h/Mpc and neutral fraction xHI greater than or similar to 0.4, which is imminently measurable by the Hydrogen Epoch of Reionization Array and future experiments. The ability of the EFT to describe the 21 -cm signal extends to simulations that have different astrophysical prescriptions for reionization as well as simulations with interacting dark matter.

Automated summary

This study develops effective field theory techniques for the 21-cm brightness temperature field during the epoch of reionization, incorporating renormalized bias and a treatment of redshift space distortions. The results show that the 21-cm brightness temperature contains direct, astrophysics-free information about the cosmological density field in redshift space, providing unique opportunities for cosmological studies. Theoretical predictions based on EFT agree well with hydrodynamical simulations and can be used in future experiments.