CAN LARGE-SCALE MAGNETIC-FIELDS SURVIVE DURING THE PRE-RECOMBINATION ERA OF THE UNIVERSE

The influence of a dense photon field on the generation of electric cu rrents and magnetic fields in the early phases of the universe is cons idered. It is shown that due to the strong interaction of charged part icles and photons, any directed relative drift velocity of positive an d negative charges is immediately thermalized and currents are shut of f. Large-scale magnetic fields caused by phase transitions evolve only under the influence of the expanding plasma, which is strongly couple d to the photons-an effect well known as Silk-damping. Immediately aft er 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 tran sition (electron-positron annihilation), the electron-photon collision s provide the effective damping. Whereas the electric conductivity due to Coulomb collisions scales as the temperature T-3/2, the photon-dri ven conductivity scales as T-3. Th, corresponding magnetic diffusion t ime scale in very early phases of the universe is too fast to allow fo r any significant macroscopic magnetic field. (C) 1998 American Instit ute of Physics. [S1070-664X(98)02507-5].