We show that in the presence of large scale primordial hypermagnetic fields , it is possible to generate a large amount of CP violation to explain the baryon to entropy ratio during the electroweak phase transition within the standard model .
The mechanism responsible for the existence of a CP violating asymmetry is the chiral nature of the fermion coupling to the background field in the symmetric phase which can be used to construct two-fermion interference processes in analogy to the Bohm-Aharanov effect .
We estimate that for strong hypermagnetic fields B _ { Y } = ( 0.3 - 0.5 ) T ^ { 2 } the baryon to entropy ratio can be \rho _ { B } / s = ( 3 - 6 ) \times 10 ^ { -11 } for slowly expanding bubble walls .