Cosmic magnetic fields from velocity perturbations in the early universe

We show, using a covariant and gauge-invariant charged multifluid perturbation scheme, that velocity perturbations of the matter-dominated dust Friedmann–Lemaître–Robertson–Walker model can lead to the generation of cosmic magnetic fields. Moreover, using cosmic microwave background constraints, it is argued that these fields can reach strengths of about 10 −28 G at the time the dynamo mechanism sets in, making them plausible seed field candidates.