Imprints of fermionic and bosonic mixed dark matter on the 21-cm signal at cosmic dawn

Abstract

The 21-cm signal from the epoch of cosmic dawn prior to reionization consists of a promising observable to gain new insights into the dark matter (DM) sector. In this paper, we investigate its potential to constrain mixed (cold + non-cold) dark matter scenarios that are characterised by the non-cold DM fraction ($f_{\mathrm{nCDM}}$) and particle mass ($m_{\mathrm{nCDM}}$). As non-cold DM species, we investigate both a fermionic (sterile neutrino) and a bosonic (ultra-light axion) particle. We show how these scenarios affect the global signal and the power spectrum using a halo-model implementation of the 21-cm signal at cosmic dawn. Next to this study, we perform an inference-based forecast study based on realistic mock power spectra from the Square Kilometre Array (SKA) telescope. Assuming inefficient, yet non-zero star-formation in minihaloes (i.e. haloes with mass below $10^8$ M${}_{\odot }$), we obtain stringent constraints on both $m_{\mathrm{nCDM}}$ and $f_{\mathrm{nCDM}}$ that go well beyond current limits. Regarding the special case of $f_{\mathrm{nCDM}}\sim 1$, for example, we find a constraint of $m_{\mathrm{nCDM}}>15$ keV (thermal mass) for fermionic DM and $m_{\mathrm{nCDM}}>2\times 10^{-20}$ eV for bosonic DM. For the opposite case of dominating cold DM, we find that at most one percent of the total DM abundance can be made of a hot fermionic or bosonic relic. All constraints are provided at the 95 percent confidence level.

19 pages, 9 figures, similar to the version accepted for publication in PRD

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