Progress on Cosmological Magnetic Fields
  A variety of observations impose upper limits at the nano Gauss level on
magnetic fields that are coherent on inter-galactic scales while blazar
observations indicate a lower bound $\sim 10^{-16}$ Gauss. Such magnetic fields
can play an important astrophysical role, for example at cosmic recombination
and during structure formation, and also provide crucial information for
particle physics in the early universe. Magnetic fields with significant energy
density could have been produced at the electroweak phase transition. The
evolution and survival of magnetic fields produced on sub-horizon scales in the
early universe, however, depends on the magnetic helicity which is related to
violation of symmetries in fundamental particle interactions. The generation of
magnetic helicity requires new CP violating interactions that can be tested by
accelerator experiments via decay channels of the Higgs particle.
