Tufts/CfA/MIT Cosmology Seminar, at MIT:

                     Tuesday March 17, 1998
                             2:30 pm
                         CTP Seminar Room

         "Magnetohydrodynamics of Early Universe and the
             Evolution of Primordial Magnetic Field"

                             Dam Son
              Massachusetts Institute of Technology

Abstract:
We show that magnetohydrodynamic turbulence leads to a more rapid growth of the correlation length of primordial magnetic field than that caused by the expansion of the Universe. As an example, we consider the magnetic fields created during the electroweak phase transition. The expansion of the universe alone would yield a correlation length at the present epoch of 1 AU, whereas we find that the correlation length is likely of order 100 AU, and cannot possibly be longer than 104 AU for non-helical fields. If the primordial field is strongly helical, the correlation length can be much larger, but we show that even in this case it cannot exceed 100 pc. All these estimates make it hard to believe that the observed galactic magnetic fields can result from seed fields generated at the electroweak phase transition. The only possibility seems to be the existence of a small-scale dynamo mechanism in the evolution of galactic (not primordial) magnetic fields, turning very short-scale field into magnetic fields with a much longer length scale.