Primordial magnetogenesis before recombination
  The origin of large magnetic fields in the Universe remains currently
unknown. We investigate here a mechanism before recombination based on known
physics. The source of the vorticity is due to the changes in the photon
distribution function caused by the fluctuations in the background photons. We
show that the magnetic field generated in the MHD limit, due to the Coulomb
scattering, is of the order $10^{-49}$~G on a coherence scale of 10 kpc. We
explicitly show that the magnetic fields generated from this process are
sustainable and are not erased by resistive diffusion. We compare the results
with current observations and discuss the implications. Our seed magnetic
fields are generated on small scales whereas the main mechanisms studied in the
literature are on scale bigger than 1 Mpc. However, compared to more exotic
theories generating seed magnetic fields on similar scales, the strength of our
fields are generally smaller.
