Prospects for probing dark matter particles and primordial black holes with the Square Kilometre Array using the 21 cm power spectrum at cosmic dawn

TL;DR

This work investigates how the Square Kilometre Array (SKA) can probe dark matter (DM) annihilation, DM decay, and primordial black hole (PBH) Hawking radiation via the 21 cm power spectrum during cosmic dawn. The authors simulate the 21 cm signal with exotic energy injection using a modified 21cmFAST pipeline informed by DarkHistory deposition efficiencies and forecast SKA sensitivities using the Fisher information matrix across DM and PBH parameters. They find that with 10,000 hours of integration, SKA could reach $\langle \sigma v \rangle \lesssim 10^{-28}$ cm$^{3}$ s$^{-1}$ for $m_\chi \sim 10$ GeV and $\tau \gtrsim 10^{28}$ s for certain DM channels, and could constrain PBH abundances to $f_{\rm PBH} \lesssim 10^{-6}$ for $M_{\rm PBH} \sim 10^{16}$ g, improving current limits by 2–4 orders of magnitude and opening sensitivity to higher PBH masses. The results emphasize the power of the 21 cm power spectrum as a multi-scale, early-universe probe of DM physics and PBHs, while noting limitations such as instrument stability for long integrations and the omission of coexisting DM processes in this study. The work points to valuable future directions, including the use of higher-order statistics and exploration of the dark ages as a cleaner laboratory for these fundamental questions.

Abstract

Probing the nature of dark matter (DM) remains an outstanding problem in modern cosmology. The 21 cm signal, as a sensitive tracer of neutral hydrogen during cosmic dawn, provides a unique means to investigate DM nature during this critical epoch. Annihilation and decay of DM particles, as well as Hawking radiation of primordial black holes (PBHs), can modify the thermal and ionization histories of the early universe, leaving distinctive imprints on the 21 cm power spectrum. Therefore, the redshifted 21 cm power spectrum serves as a powerful tool to investigate such DM processes. In this work, we systematically assess the potential of the upcoming Square Kilometre Array (SKA) to constrain DM and PBH parameters using the 21 cm power spectrum. Assuming $10,000$ hours of integration time, the SKA is projected to reach sensitivities of $\langleσv\rangle \leq 10^{-28}\,{\rm cm}^{3}\,{\rm s}^{-1}$ and $τ\geq 10^{28}\,{\rm seconds}$, for $10\,{\rm GeV}$ DM particles. It can also probe PBHs with masses of $10^{16}\,\mathrm{g}$ and abundances $f_{\mathrm{PBH}} \leq 10^{-6}$. These results indicate that the SKA could place constraints on DM annihilation, decay, and PBH Hawking radiation that are up to two to three orders of magnitude stronger than current limits. Furthermore, the SKA is expected to exceed existing bounds on sub-GeV DM and to probe Hawking radiation from PBHs with masses above $10^{17}\,{\rm g}$, which are otherwise inaccessible by conventional cosmological probes. Overall, the SKA holds great promise for advancing our understanding of both DM particles and PBHs, potentially offering new insights into the fundamental nature of DM.

Figures (12)

• Figure 1: Lightcone slices of the differential brightness temperature in our $(250~{\rm Mpc})^{3}$ large simulation box. The fiducial model are shown on the upper panel. The bottom panel show the slice with DM particle annihilation through $\chi\rightarrow e^{+}e^{-}$ channel with $m_{\chi} = 10 ~\rm{GeV}$ and $\tau = 10^{27}\, s$.
• Figure 2: The 21 cm power spectrum under different energy injection scenarios. Left panels: The 21 cm power spectrum as a function of redshift $z$ at fixed scales $k = 0.2 \,\rm Mpc^{-1}$ and $k = 0.73\,\rm Mpc^{-1}$. Right panels: The 21 cm power spectrum as a function of the scale at redshift $z = 8.2$ and $z = 10.6$. In each panel, the instrumental noise is shown by the shaded region. Black curves show the 21 cm power spectrum of the fiducial model. Red curves show 21 cm power spectrum with DM particle annihilation through $\chi\chi\rightarrow e^{+}e^{-}$ channel with $m_{\chi} = 10 ~\rm{GeV}$ and $\langle \sigma v \rangle = 10^{-26}\, \rm{cm}^{3}\,s^{-1}$. Blue curves show 21 cm power spectrum with DM particle decay through $\chi\rightarrow e^{+}e^{-}$ channel with $m_{\chi} = 10 ~\rm{GeV}$ and $\tau = 10^{27}\,\rm{s}$. Green curves show 21 cm power spectrum with PBH Hawking radiation, with $M_{\rm PBH} = 10^{16} ~\rm{g}$ and $f_{\rm PBH} = 10^{-5}$.
• Figure 3: Fisher forecast for probing DM annihilation through the $\chi \chi \rightarrow e^{+} e^{-}$ channel using the 21 cm power spectrum by the SKA. $1\sigma$ and $2\sigma$ confidence intervals are represented by dark and light shaded areas, respectively, with solid curves indicating the marginalized posteriors. Fiducial model used is consistent with that shown in Fig. \ref{['fig:measurement error power']}. The assumed DM particle mass is $m_{\chi} = 100$ MeV, integrated over $10,000$ hours.
• Figure 4: Prospective sensitivity of the SKA for probing the annihilation of DM particles through three channels. The $1\sigma$ confidence-level sensitivity of the SKA to the thermally averaged annihilation cross section of DM particles (mass range $10^{6}$-$10^{12}\,\text{eV}$) are shown by the red curves. Existing $2\sigma$ upper limits from observations of CMB distortion (black curve) Zhang:2023usm, gamma-ray observations (gray curves) Cirelli:2020bpcHESS:2018komHESS:2014zqaVERITAS:2017tifMAGIC:2017avyAleksic:2013xeaFermi-LAT:2015att, and electron-positron pairs (gray dashed curve) Cohen:2016uygBoudaud:2018oya are included for comparison. Prospective sensitivity of the 21 cm global spectrum (blue curve) Zhao:2024jad is also included for comparison.
• Figure 5: Fisher forecast for probing DM decay through the $\chi \rightarrow e^{+} e^{-}$ channel using the 21 cm power spectrum by the SKA. $1\sigma$ and $2\sigma$ confidence intervals are represented by dark and light shaded areas, respectively, with solid curves indicating the marginalized posteriors. Fiducial model used is consistent with that shown in Fig. \ref{['fig:measurement error power']}. The assumed DM particle mass is $m_{\chi} = 100$ MeV, integrated over $10,000$ hours.