The seed magnetic field generated during recombination

Understand

Nonlinear dynamics creates vortical currents when the tight-coupling approximation between photons and baryons breaks down around the time of recombination.

• This generates a magnetic field at second order in cosmological perturbations, whose power spectrum is fixed by standard physics, without the need for any ad hoc assumptions.
• We present the fully relativistic calculation of the magnetic power spectrum, including the effects of metric perturbations, second-order velocity and the photon anisotropic stress, thus generalizing and correcting previous results.
• We also show that significant magnetogenesis continues to occur after recombination.