Extragalactic magnetic fields unlikely generated at the electroweak
  phase transition
  In this letter we show that magnetic fields generated at the electroweak
phase transition are most likely too weak to explain the void magnetic fields
apparently observed today unless they have considerable helicity. We show that,
in the simplest estimates, the helicity naturally produced in conjunction with
the baryon asymmetry is too small to explain observations, which require a
helicity fraction at least of order $10^{-14}-10^{-10}$ depending on the void
fields constraint used. Therefore new mechanisms to generate primordial
helicity are required if magnetic fields generated during the electroweak phase
transition should explain the extragalactic fields.
