Primordial magnetic fields and CMB anisotropies

Possible signatures of primordial magnetic fields on the Cosmic Microwave Background (CMB) temperature and polarization anisotropies are reviewed. The signals that could be searched for include excess temperature anisotropies particularly at small angular scales below the Silk damping scale, B‐mode polarization, and non‐Gaussian statistics. A field at a few nG level produces temperature anisotropies at the 5 µK level, and B‐mode polarization anisotropies 10 times smaller, and is therefore potentially detectable via the CMB anisotropies. An even smaller field, with B 0 < 0.1 nG, could lead to structure formation at high redshift z > 15, and hence naturally explain an early re‐ionization of the Universe. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)