Unveiling the nature of dark matter with high redshift 21 cm line experiments

TL;DR

This paper investigates how annihilating dark matter influences the 21 cm signal from the early Universe, revealing distinctive signatures in the signal's evolution that can be detected with upcoming experiments.

Contribution

It models the impact of 10 GeV WIMP dark matter annihilations on the 21 cm signal using 21cmFAST, identifying unique, robust signatures in the signal's evolution.

Findings

Dark matter annihilations heat the IGM earlier and more uniformly.

Distinctive signatures in the 21 cm power spectrum are identified.

Decaying warm dark matter has negligible heating effects.

Abstract

Observations of the redshifted 21 cm line from neutral hydrogen will open a new window on the early Universe. By influencing the thermal and ionization history of the intergalactic medium (IGM), annihilating dark matter (DM) can leave a detectable imprint in the 21 cm signal. Building on the publicly available 21cmFAST code, we compute the 21 cm signal for a 10 GeV WIMP DM candidate. The most pronounced role of DM annihilations is in heating the IGM earlier and more uniformly than astrophysical sources of X-rays. This leaves several unambiguous, qualitative signatures in the redshift evolution of the large-scale ($k\approx0.1$ Mpc$^{-1}$) 21 cm power amplitude: (i) the local maximum (peak) associated with IGM heating can be lower than the other maxima; (ii) the heating peak can occur while the IGM is in emission against the cosmic microwave background (CMB); (iii) there can be a dramatic drop in power (a global minimum) corresponding to the epoch when the IGM temperature is comparable to the CMB temperature. These signatures are robust to astrophysical uncertainties, and will be easily detectable with second generation interferometers. We also briefly show that decaying warm dark matter has a negligible role in heating the IGM.