Jennifer Schober

For a long time, the strength of the primordial magnetic field could only be constrained from above, e.g. from Big Bang nucleosynthesis and the cosmic microwave background. But evidence for the existence of primordial magnetic fields accumulates.

If primordial magnetic fields can survive until the present or not, depends on their initial field strength B, their correlation length L, as well as on their helicity. Magnetic helicity, a topological property of the vector field which measures the extent to which the field lines wrap and coil around one another, can be approximated by L B^2. Since helicity is a conserved quantity in ideal classical MHD, L increases as B decays [the so-called inverse cascade].

However, classical MHD is not applicable for the high-energy plasma filling the early Universe. A standard model particle physics effect alters the evolution equations within the first seconds of the Universe significantly. This effect is the chiral magnetic effect (CME) [see the figure], which describes the generation of an electric current along a magnetic field in presence of an asymmetry of the number density of left- and right-handed fermions. This can cause a magnetic field instability.

To go beyond the analytical studies of this instability in the early Universe, we are performing 3D simulations of this effect in an extended MHD framework. Our simulations reveal how a chiral dynamo instability generates turbulence that in turn can fuel a large-scale dynamo.