Weak Primordial Magnetic Fields and Anisotropies in the Cosmic Microwave
  Background Radiation
  It is shown that small-scale magnetic fields present before recombination
induce baryonic density inhomogeneities of appreciable magnitude. The presence
of such inhomogeneities changes the ionization history of the Universe, which
in turn decreases the angular scale of the Doppler peaks and increases Silk
damping by photon diffusion. This unique signature could be used to (dis)prove
the existence of primordial magnetic fields of strength as small as B~10^(-11)
Gauss by upcoming cosmic microwave background observations.
