Can large-scale magnetic fields survive during the pre-recombination era of the universe?

Abstract

The influence of a dense photon field on the generation of electric currents and magnetic fields in the early phases of the universe is considered. It is shown that due to the strong interaction of charged particles and photons, any directed relative drift velocity of positive and negative charges is immediately thermalized and currents are shut off. Large-scale magnetic fields caused by phase transitions evolve only under the influence of the expanding plasma, which is strongly coupled to the photons—an effect well known as Silk-damping. Immediately after the epoch of baryon–antibaryon annihilation, this damping mechanism results in a radiation dominated electric conductivity that is mainly determined by the proton–photon collisions. After the next phase transition (electron–positron annihilation), the electron–photon collisions provide the effective damping. Whereas the electric conductivity due to Coulomb collisions scales as the temperature T3/2, the photon-driven conductivity scales as T−3. The corresponding magnetic diffusion time scale in very early phases of the universe is too fast to allow for any significant macroscopic magnetic field.