Can Conformal and Disformal Couplings Between Dark Sectors Explain the
  EDGES 21cm Anomaly?
  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 $\Lambda$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 21cm 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
21cm 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.
