Primordial magnetic fields, anomalous matter-antimatter fluctuations, and big bang nucleosynthesis

We show that the presence of primordial stochastic (hypercharge) magnetic fields before the electroweak phase transition (EWPT) induces baryon-antibaryon inhomogeneities. Depending on the magnetic field spectrum and on the particle physics parameters (such as the strength of the EWPT and electron Yukawa couplings), these fluctuations may survive until the big bang nucleosynthesis (BBN). Their length scale and magnitude can be so large that sizable antimatter domains are present. This provides the possibility of a new type of initial conditions for nonhomogeneous BBN or stringent bounds on primordial magnetic fields.