Cosmological bounds on dark matter annihilation using dark ages 21-cm signal

TL;DR

This paper uses the dark ages 21-cm signal to set new constraints on dark matter annihilation, providing bounds that surpass previous limits for dark matter masses below 10 GeV.

Contribution

It introduces a method to constrain dark matter annihilation using the dark ages 21-cm signal, reducing astrophysical uncertainties compared to other approaches.

Findings

Derived an upper bound of $f_\chi^2\langle\sigma v\rangle/M_\chi \lesssim 10^{-27}$ cm$^3$ s$^{-1}$ GeV$^{-1}$.

Stronger constraints than Planck data for dark matter masses below 10 GeV.

Constraints are robust against future experimental and cosmological uncertainties.

Abstract

We investigate the impact of dark matter (DM) annihilation on the global 21-cm signal during the dark ages and cosmic dawn eras. The 21-cm line provides a complementary probe for studying the nature of dark matter beyond standard cosmological observables. In the standard $\Lambda$CDM framework, the expected absorption amplitude of the dark ages global 21-cm signal is approximately $-42\, \rm mK$. However, energy injection from DM annihilation can significantly heat and ionize the intergalactic medium, potentially altering or even erasing this absorption feature. We evaluate the thermal and ionization history of the gas to derive an upper bound on $f_\chi^2 \langle \sigma v \rangle / M_\chi$ using the dark ages signal, which is free from astrophysical uncertainties. After incorporating observational and theoretical uncertainties arising from future lunar-based experiments and variations in cosmological parameters, respectively -- we obtain a conservative upper limit of $f_\chi^2\langle\sigma v\rangle/M_\chi \lesssim 10^{-27}~\rm cm^3\,s^{-1}\,\rm GeV^{-1}$. This constraint is stronger than the bounds derived from Planck (2018) data for mass $\lesssim 10~\rm GeV$.