21cm fluctuations from primordial magnetic fields
  Recent observations of magnetic fields in intergalactic void regions and in
high redshift galaxies may indicate that large scale magnetic fields have a
primordial origin. If primordial magnetic fields were present soon after the
recombination epoch, they would have induced density fluctuations on the one
hand and dissipated their energy into the primordial gas on the other, and
thereby significantly alter the thermal history of the Universe. Here we
consider both the effects and calculate the brightness temperature fluctuations
of the 21cm line using simple Monte Carlo simulations. We find that the
fluctuations of the 21cm line from the energy dissipation appear only on very
small scales and those from the density fluctuations always dominate on
observationally relevant angular scales.
