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arXiv · 2310.15530

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

Rajesh Mondal·Rennan Barkana·Anastasia Fialkov
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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 $A_{\rm r}=0.4$, where $A_{\rm r}$ 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$σ$ significance (compared to $4.1\,σ$ for the standard signal) and can be distinguished from the standard (no ERB) signal at $8.5\,σ$, 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 $4.7-7.2\,σ$, and it could be distinguished from the standard at $2.2-9.3\,σ$. 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.

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Rajesh Mondal, Rennan Barkana, Anastasia Fialkov. 2023-11-08. Constraining exotic dark matter models with the dark ages 21-cm signal. https://doi.org/10.1093/mnras%2Fstad3317

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