Early dark energy effects on the 21-cm signal

Early dark energy (EDE) is one of the leading models proposed to resolve the perplexing Hubble tension. Despite extensive scrutiny and testing against various observables, conclusive constraints remain elusive as we await new data. In this paper, we study the impact of EDE on the 21-cm signal, a powerful probe of cosmic dawn, and the epoch of reionization. First, we examine the signatures of the shift in cosmological parameters and the new EDE parameters on the evolution of the 21-cm signal compared to $\mathrm{\ensuremath{\Lambda}}$ cold dark matter ($\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$). We then focus on the implications of these signatures for upcoming radio interferometer telescopes, such as the Hydrogen Epoch of Reionization Array (HERA), and their ability to differentiate between EDE and $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$. Finally, we forecast HERA's sensitivity to the fractional energy density of EDE, ${f}_{\mathrm{EDE}}$, assuming a fiducial EDE model. We find significant modifications to the 21-cm signal due to the presence of EDE. Furthermore, our analysis suggests that HERA, operating in its designed configuration, is poised to differentiate between the models and be sensitive to ${f}_{\mathrm{EDE}}$ within $2\ensuremath{\sigma}$ after $\mathcal{O}(100)\text{ }\text{ }\mathrm{days}$ of observation and $5\ensuremath{\sigma}$ after two years.