Fuzzy Dark Matter and the 21 cm Power Spectrum

We model the 21 cm power spectrum across the Cosmic Dawn and the Epoch of Reionization (EoR) in fuzzy dark matter (FDM) cosmologies. The suppression of low-mass halos in FDM models leads to a delay in the onset redshift of these epochs relative to cold dark matter (CDM) scenarios. This strongly impacts the 21 cm power spectrum and its redshift evolution. The 21 cm power spectrum at a given stage—i.e., compared at fixed average brightness temperature but varying redshift—of the EoR/Cosmic Dawn process is also modified: in general, the amplitude of 21 cm fluctuations is boosted by the enhanced bias factor of galaxy-hosting halos in FDM. We forecast the prospects for discriminating between CDM and FDM with upcoming power spectrum measurements from HERA, accounting for degeneracies between astrophysical parameters and dark matter properties. If FDM constitutes the entirety of the dark matter and the FDM particle mass is 10⁻²¹ eV, HERA can determine the mass to within 20% at 2σ confidence.