Constraining exotic dark matter models with the dark ages 21-cm signal

Abstract

The dark ages 21-cm signal is a powerful tool for precision cosmology and probing new physics. We study two non-standard models: an excess radio background (ERB) model (possibly generated by dark matter decay) and the millicharged dark matter (mDM) model. These models were inspired by the possible EDGES detection of a strong global 21-cm absorption during cosmic dawn, but more generally they provide a way to anticipate the potential discovery space. During the dark ages the 21-cm global signal in the ERB model reaches a saturated form for an amplitude $A_{\mathrm{r}}=0.4$, where $A_{\mathrm{r}}$ is the radio background intensity at cosmic dawn relative to the cosmic microwave background. This amplitude is one-fifth of the minimum required to explain the EDGES signal, and corresponds to just 0.1% of the observed extragalactic background; it would give a signal that can be detected at 5.9$\sigma$ significance (compared to $4.1\sigma$ for the standard signal) and can be distinguished from the standard (no ERB) signal at $8.5\sigma$, all with a 1,000 hr global signal measurement. The 21-cm power spectrum has potentially more information, but far greater resources would be required for comparable constraints. For the mDM model, over a range of viable parameters, the global signal detection significance would be $4.7-7.2\sigma$, and it could be distinguished from the standard at $2.2-9.3\sigma$. With an array of global signal antennas achieving an effective 100,000 hr integration, the significance would be $10\times$ better. Our analysis helps motivate the development of lunar and space-based dark ages experiments.

Published in Monthly Notices of the Royal Astronomical Society

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• A Bayesian approach to modelling spectrometer data chromaticity corrected using beam factors -- II. Model priors and posterior odds
• Probing self-interacting ultrahigh-energy neutrinos with the cosmic 21-cm signal
• The impact of lunar topography on the 21-cm power spectrum for grid-based arrays : Insights for the Dark-ages EXplorer (DEX)
• The magnitude of the dark ages 21-cm signal in the context of existing early and late time constraints on $\Lambda$CDM