The recently announced result by EDGES points an unexpected excess in the 21-cm global brightness temperature from cosmic dawn at $z\sim 17$, potentially indicating new phenomena beyond the $\mathrm{<ruby><rb>\Lambda </rb><rt>らむだ</rt></ruby>}\mathrm{CDM}$ model. A generic cosmological model which allows conformal and disformal couplings between dark matter and dark energy is employed to investigate the impact on the 21-cm absorption signal and understand the EDGES anomaly. After exploring a wide range of parameter space for couplings, we find that the coupling effects can lead to a moderate change in the Hubble parameter while a negligible change in the spin temperature in the early Universe. Consequently, the decrease of the Hubble parameter from the mixed conformal and disformal couplings can reproduce the 21-cm absorption approximately in consistent with the EDGES result at $z=17.5$. However, there is still tension in corresponding parameter space between EDGES and other cosmological observations for this model.

• Received 16 July 2018

DOI:https://doi.org/10.1103/PhysRevD.99.023528