LIMITS ON POSSIBLE MAGNETIC-FIELDS AT NUCLEOSYNTHESIS TIME

In this paper we discuss limits on magnetic fields that could have bee n present at nucleosynthesis time. We considered several effects that could be relevant modifing light elements relic abundances. They inclu de: changes in reaction rates, mass shifts due to strong and electroma gnetic interactions, variation of the expansion rate of the Universe d ue to both the magnetic field energy density and the increasing of the electrons density in overcritical magnetic fields. We find that the l atter is the main effect. It was not taken into account in previous ca lculations. The allowed field intensity at the end of nucleosynthesis (T = 1 x 10(9) K) is B less than or equal to 3 x 10(10) gauss.