PRIMORDIAL MAGNETIC-FIELDS, ANOMALOUS MATTER-ANTIMATTER FLUCTUATIONS,AND BIG-BANG NUCLEOSYNTHESIS

We show that the presence of primordial stochastic (hypercharge) magne tic fields before the electroweak phase transition (EWPT) induces bary on-antibaryon inhomogeneities. Depending on the magnetic field spectru m and on the particle physics parameters (such as the strength of the EWPT and electron Yukawa couplings), these fluctuations may survive un til the big bang nucleosynthesis (BBN). Their length scale and magnitu de can be so large that sizable antimatter domains are present. This p rovides the possibility of a new type of initial conditions for nonhom ogeneous BBN or stringent bounds on primordial magnetic fields.