STRONGLY FIRST-ORDER ELECTROWEAK PHASE-TRANSITION INDUCED BY PRIMORDIAL HYPERMAGNETIC FIELDS

We consider the effect of the presence of a hypermagnetic field at the electroweak phase transition. Screening of the Z-component inside a b ubble of the broken phase delays the phase transition and makes it str onger first order. We show that the sphaleron constraint can be evaded for m(H) up to 100 GeV if a B-Y greater than or similar to 0.3T(2) ex ists at the time of the EW phase transition, thus resurrecting the pos sibility for baryogenesis within the minimal standard model (provided enough CP violation can be obtained). We estimate that for m(H) greate r than or similar to 100 GeV the Higgs condensate behaves like a type II superconductor with Z-vortices penetrating the bubble. Also, for su ch high Higgs masses the minimum B-Y field required for a strong first order phase transition is large enough to render the W-field unstable towards forming a condensate which changes the simple picture of the symmetry breaking. (C) 1998 Elsevier Science B.V. All rights reserved.