Origin and evolution of cosmic magnetic fields

Observations of blazars suggest that the intergalactic medium is permeated by large-scale magnetic fields. This might be the first sign of relics of primordial fields and can help us to solve one of the greatest mysteries in modern cosmology: the origin of cosmic magnetic fields. To shed new light on primordial magnetism, I will present an extended theory of magnetohydrodynamics (MHD) which is suitable to model the relativistic plasma less than a second after the Big Bang. The set of equations includes a description of the asymmetry between left- and right-handed fermions. Such a chiral asymmetry can give rise to an electric current along the magnetic field that in turn can trigger an instability in the magnetic field. Using direct numerical simulations with the Pencil Code, I study the amplification of weak magnetic seed fields via chiral MHD dynamos. I will discuss the evolution of these magnetic fields from the early Universe until today. For different scenarios, I will make predictions for the properties of intergalactic magnetic fields.