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Interacting Dark Energy: Possible Explanation for 21-cm Absorption at Cosmic Dawn

Andre A. Costa, Ricardo C. G. Landim, Bin Wang, E. Abdalla

TL;DR

The paper investigates whether an interaction between dark matter and dark energy can explain the anomalously deep 21-cm absorption detected by EDGES at cosmic dawn. By adopting two simple phenomenological couplings, $Q = 3 H (\xi_1 \rho_c + \xi_2 \rho_d)$, and solving the modified continuity equations, the authors show that the DM–DE interaction modifies the background expansion, notably $H(z)$, thereby increasing the optical depth and the brightness temperature $T_{21}$ without altering the gas or radiation temperatures. They provide analytic solutions for the energy densities, discuss stability constraints, and compute $T_{21}$ for representative couplings, showing that larger positive couplings can raise the absorption signal but may clash with other cosmological constraints; negative couplings can reduce or reverse the effect. They conclude that while the model can somewhat reconcile EDGES within current bounds, achieving the exact observed amplitude would require strong couplings, and future 21-cm observations can constrain the DM–DE coupling and break degeneracies with $\omega$.

Abstract

A recent observation points to an excess in the expected 21-cm brightness temperature from cosmic dawn. In this paper, we present an alternative explanation of this phenomenon, an interaction in the dark sector. Interacting dark energy models have been extensively studied recently and there is a whole variety of such in the literature. Here we particularize to a specific model in order to make explicit the effect of an interaction.

Interacting Dark Energy: Possible Explanation for 21-cm Absorption at Cosmic Dawn

TL;DR

The paper investigates whether an interaction between dark matter and dark energy can explain the anomalously deep 21-cm absorption detected by EDGES at cosmic dawn. By adopting two simple phenomenological couplings, , and solving the modified continuity equations, the authors show that the DM–DE interaction modifies the background expansion, notably , thereby increasing the optical depth and the brightness temperature without altering the gas or radiation temperatures. They provide analytic solutions for the energy densities, discuss stability constraints, and compute for representative couplings, showing that larger positive couplings can raise the absorption signal but may clash with other cosmological constraints; negative couplings can reduce or reverse the effect. They conclude that while the model can somewhat reconcile EDGES within current bounds, achieving the exact observed amplitude would require strong couplings, and future 21-cm observations can constrain the DM–DE coupling and break degeneracies with .

Abstract

A recent observation points to an excess in the expected 21-cm brightness temperature from cosmic dawn. In this paper, we present an alternative explanation of this phenomenon, an interaction in the dark sector. Interacting dark energy models have been extensively studied recently and there is a whole variety of such in the literature. Here we particularize to a specific model in order to make explicit the effect of an interaction.

Paper Structure

This paper contains 5 sections, 6 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Brightness Temperature
  3. Interacting Model
  4. Results
  5. Conclusions

Figures (2)

  • Figure 1: Hubble parameter as a function of redshift for different values of the interaction. (a) Model proportional to the energy density of DE, $Q = 3H\xi_2\rho_d$. (b) Model proportional to the energy density of DM, $Q = 3H\xi_1\rho_c$.
  • Figure 2: 21-cm brightness temperature as a function of the interaction parameter and the equation of state at $z = 20$. (a) Model proportional to the energy density of DE, $Q = 3H\xi_2\rho_d$. (b) Model proportional to the energy density of DM, $Q = 3H\xi_1\rho_c$.