Signatures of inhomogeneous dark matter annihilation on 21-cm

TL;DR

This paper investigates how inhomogeneous dark matter annihilation, amplified by structure formation, can significantly increase fluctuations in the 21-cm signal during cosmic dawn, offering potential observational signatures.

Contribution

It introduces a model for the inhomogeneous enhancement of dark matter annihilation effects on the 21-cm signal, highlighting its impact on temperature and ionization fluctuations.

Findings

Inhomogeneous DM annihilation can boost 21-cm power spectrum by up to 130 times.

Effects are significant at redshifts 11-16 and scales 0.05-3 Mpc^{-1}.

Potential detectability with upcoming radio telescopes like SKA.

Abstract

The energy released from dark matter (DM) annihilation leads to additional ionization and heating of the intergalactic gas, impacting the hydrogen 21-cm signal during the cosmic dawn. The dark matter annihilation rate scales with its density squared and becomes inhomogeneously boosted with structure formation. This paper examines the inhomogeneity in DM annihilation rate induced by the growth of DM halo structures, and we show that this effect can significantly amplify the spatial fluctuations in temperature and ionization fraction of the gas. Consequently, the fluctuations in the 21-cm brightness temperature may also be enhanced. We showcase these effects for a DM mass of 100 MeV annihilating into $\rm{e}^-\rm{e}^+$ at a rate of $\left<\sigma v\right>/m_\chi \sim 10^{-27} {\rm cm^3 s^{-1} GeV^{-1}}$, which is consistent with current constraints set by the cosmic microwave background. We find that, compared to the homogeneous calculations, inhomogeneous annihilation can enhance the 21-cm power spectrum by up to a factor of 130 over the scales of $k \in [0.05, 3]\ {\rm{Mpc^{-1}}}$ at redshifts $11-16$. Such signatures could potentially be detected by upcoming radio observatories such as the Square Kilometer Array telescope.