Stronger 21cm absorption from charge sequestration

The unexpectedly strong 21cm absorption signal detected by the EDGES experiment suggests that the baryonic gas at the end of the dark ages was colder than predicted within the standard cosmological scenario. I will introduce one novel mechanism to lower the baryon temperature after recombination. The model includes a stable, negatively-charged particle with a significant cosmological abundance, such that the universe remains charge-neutral but the electron and proton numbers are no longer equal. The deficit of electrons after recombination results in an earlier decoupling of the baryon and CMB temperatures, and thus in a colder gas at the cosmic dawn. I will discuss the phenomenological constraints and possible smoking guns of this scenario.