# Forecasting 21-cm power spectrum sensitivity to dark Matter-baryon scattering

## TL;DR

Upcoming 21-cm observations can greatly enhance constraints on dark matter-baryon interactions, especially for velocity-dependent cross-sections, surpassing current bounds and emphasizing the importance of astrophysical uncertainty modeling.

## Contribution

This study provides detailed forecasts of 21-cm power spectrum sensitivity to dark matter-baryon scattering, including velocity dependence and astrophysical uncertainties, using simulations and Fisher analysis.

## Key findings

- 21-cm power spectrum can improve dark matter-baryon scattering constraints by over an order of magnitude.
- Sensitivity varies with velocity dependence of the cross-section, with stronger improvements for Coulomb-like interactions.
- Dark matter-baryon cross-section shows no correlation with star formation parameters but correlates with X-ray luminosity.

## Abstract

We explore the potential of upcoming 21-cm interferometric observations to probe interacting dark matter (IDM). We focus on scenarios where the dark matter-baryon scattering cross-section scales as $\sigma(v) =\sigma_{0} v^n$, with $\sigma_{0}$ being the normalization constant, $v$ the relative velocity between dark matter and baryons, and $n$ characterizing the velocity dependence. Specifically, we emphasize two cases: Coulomb-like interaction ($n = -4$) and velocity-independent interaction ($n = 0$). Using detailed simulations of the 21-cm power spectrum and the Fisher matrix formalism, we forecast the sensitivity of the Hydrogen Epoch of Reionization Array (HERA), which targets the frequency range 50-225 MHz, to both IDM and astrophysical parameters. We marginalize over key astrophysical uncertainties, including star formation efficiency, ionizing photon escape fraction, and X-ray luminosity. Our results demonstrate that 21-cm power spectrum measurements can significantly improve sensitivity to IDM cross-section, with at least a factor of five improvement over global signal forecasts for the $n=0$ case, and more than an order of magnitude enhancement for the $n=-4$ scenario. These forecasts also significantly improve upon the existing bounds from cosmic microwave background and Milky Way satellite abundance observations. Our analysis also shows that the IDM cross-section exhibits no correlation with the parameters associated with star formation efficiency and ionizing photon escape fraction of Population-II stars. However, we find that the Coulomb-like cross-section is positively correlated with X-ray luminosity. Our results highlight the critical role of accounting for astrophysical uncertainties in obtaining robust inferences of dark matter-baryon interactions from future 21-cm power spectrum observations.