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

Chunlong Li,Xin Ren,Martiros Khurshudyan,Yi-Fu Cai

doi:10.1016/j.physletb.2019.135141

Abstract

In this Letter 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 of them is the change in 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 influence of linear IDE models on 21-cm line signals and find that under the current observational constraints, it is difficult to yield a sufficiently strong 21-cm line signal to be consistent with the results of Experiment to Detect the Global Epoch of reionization Signature (EDGES) since only the optical depth could be effectively changed in these models. Accordingly, this implies us to construct a background evolution which could fulfill the reasonable change of optical depth and Compton heating decoupling time at the same moment by introducing an early dark energy dominated stage into the evolution governed by the IDE models. The comparison with astronomical observations indicate that this scenario could only alleviate, but not complete eliminate, the tension between EDGES and other cosmological surveys.

Highlights

The underlying physics of the 21-cm line signal in the early Universe has become a hot topic since the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) reported an excess of the 21-cm absorption line around the epoch of cosmic dawn
We investigate the influence of linear interacting dark energy (IDE) models on 21-cm line signals and find that under the current observational constraints, it is difficult to yield a sufficiently strong 21-cm line signal to be consistent with the results of Experiment to Detect the Global Epoch of reionization Signature (EDGES) since only the optical depth could be effectively changed in these models
In this Letter, we studied the implications of the possible excess of the 21-cm global signal around cosmic dawn on the cosmological expansion of the early Universe

Summary

INTRODUCTION

The underlying physics of the 21-cm line signal in the early Universe has become a hot topic since the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) reported an excess of the 21-cm absorption line around the epoch of cosmic dawn. We point out that a specific background evolution would directly yield an impact on the optical depth of the hydrogen cloud and the decoupling time of the Compton-heating process [46] Both could have considerable influence on the final strength of the 21-cm line signal at the epoch of cosmic dawn. There exists the severe tension between the limits of EDGES and other experiments, the analysis of what degree could the optical depth and Compton heating decoupling time be affected leads us to a more suitable form of the evolution for the Hubble parameter to be consistent with an anomalously strong 21-cm absorption feature We fulfill this scenario by introducing a cosmological phase dominated by dynamical dark energy at early time and discuss the feasibility of this scenario under current observational constraints on the paradigm of IDE. Around the corresponding redshift (z 17) during the cosmic dawn, the recombination process had already finished, and this mechanism can hardly produce a signature of observable interest

THE IDE MODELS AND AN EXCESS OF 21-CM LINE SIGNAL

Mechanisms of affecting the global 21-cm lines

AN EARLY DARK ENERGY DOMINATED STAGE

CONCLUSIONS