Neutron oscillation and the primordial magnetic field

Abstract

The phenomenon of neutron-antineutron oscillations, recently proposed as a novel consequence of grand unified theories, permits limits to be placed on any primordial field present during the nucleosynthetic stage of the big bang. It is shown that the sensitive dependence of these oscillations on the magnetic field places another stringent lower limit on the primordial magnetic field. The conversion rate is inversely proportional to the square of the magnetic field, and a lower limit is arrived at by assuming that the availability of neutrons for helium production is not depleted. Expressions are derived for the value of the relic magnetic field at a temperature of about 0.1 Mev and for the present strength of this relic field.