# Dawn of the dark: unified dark sectors and the EDGES Cosmic Dawn 21-cm signal

## TL;DR

This paper investigates how the EDGES Cosmic Dawn 21-cm signal can constrain unified dark sector models, specifically generalized Chaplygin gas, reducing parameter uncertainties and alleviating Hubble tension.

## Contribution

It demonstrates that incorporating the EDGES 21-cm data significantly tightens constraints on unified dark sector models and reduces the Hubble constant tension.

## Key findings

- Uncertainties on Chaplygin gas parameters are reduced by a factor of 1.5 to 10.
- The Hubble tension decreases from 4σ to 1.3σ within the generalized Chaplygin gas model.
- The 21-cm signal provides a new probe for testing dark sector physics.

## Abstract

While the origin and composition of dark matter and dark energy remains unknown, it is possible that they might represent two manifestations of a single entity, as occurring in unified dark sector models. On the other hand, advances in our understanding of the dark sector of the Universe might arise from Cosmic Dawn, the epoch when the first stars formed. In particular, the first detection of the global 21-cm absorption signal at Cosmic Dawn from the EDGES experiment opens up a new arena wherein to test models of dark matter and dark energy. Here, we consider generalized and modified Chaplygin gas models as candidate unified dark sector models. We first constrain these models against Cosmic Microwave Background data from the \textit{Planck} satellite, before exploring how the inclusion of the global 21-cm signal measured by EDGES can improve limits on the model parameters, finding that the uncertainties on the parameters of the Chaplygin gas models can be reduced by a factor between $1.5$ and $10$. We also find that within the generalized Chaplygin gas model, the tension between the CMB and local determinations of the Hubble constant $H_0$ is reduced from $\approx 4\sigma$ to $\approx 1.3\sigma$. In conclusion, we find that the global 21-cm signal at Cosmic Dawn can provide an extraordinary window onto the physics of unified dark sectors.