# Implications of the possible 21-cm line excess at cosmic dawn on dynamics of interacting dark energy

## TL;DR

This study explores how interacting dark energy models affect the 21-cm line signal during cosmic dawn, proposing modifications to the Hubble parameter evolution to reconcile experimental tensions.

## Contribution

It introduces a new early dark energy stage within IDE models to address discrepancies in 21-cm line observations and other cosmological data.

## Key findings

- Optical depth significantly affected by IDE models.
- Early dark energy stage can reduce tension with EDGES data.
- Complete resolution of tension remains unachieved.

## Abstract

In this paper we study implications of the possible excess of 21-cm line global signal at the epoch of cosmic dawn on the evolutions of a class of dynamically interacting dark energy (IDE) models. We firstly summarize two dynamical mechanisms in which different background evolutions can exert considerable effects on the 21-cm line global signal. One is the decoupling time of Compton scattering heating, the other stems from the direct change of optical depth due to the different expansion rate of the Universe. After that, we investigate the IDE models to illustrate the tension between the results of Experiment to Detect the Global Epoch of reionization Signature (EDGES) and other experiments. To apply the analyses of these two mechanisms to IDE models, we find that only the optical depth can be significantly changed. Accordingly, in order to relieve the tension by including the effects of the decoupling time of Compton scattering heating, we deduce a possible evolution form for the Hubble parameter within IDE that begins at an early stage around $z\sim 100$ and then smoothly evolves to a value at $z\sim 17$ which is smaller than that obtained in the standard paradigm. Eventually, we fulfill this scenario by adding an early dark energy dominated stage to the cosmological paradigm described by IDE models, which can alleviate the tension between EDGES and other cosmological observations but cannot completely solve it.