EDGES signal in presence of magnetic fields
  We study the 21-cm differential brightness temperature in the presence of
primordial helical magnetic fields for redshift $z=10-30$. We argue that the
$\alpha$-effect that sets in at earlier time can be helpful in lowering the gas
temperature to 3.2 degrees Kelvin at $z=17$. This effect can arise in the early
Universe due to some parity violating high energy processes. Using the EDGES
(Experiment to Detect the Global Epoch of Reionization Signature) results, we
find the upper and lower limits on the primordial magnetic field to be $6\times
10^{-3}~{\rm nG} $ & $5\times 10^{-4}~{\rm nG}$ respectively. We also discuss
the effect of Ly$\alpha$ background on the bounds. Our results do not require
any new physics in terms of dark matter.
