Lepton Asymmetry with Primordial Magnetic Fields

Abstract

If the neutrino are Majorana particles, the neutrino spin flavor precession induced ΔL = 2 processes which could be relevant for leptogenesis depending on the strength of neutrino magnetic moments and magnetic fields. Although the extra galactic magnetic fields is extremely weak at present time (about 10−9 Gauss), the primordial magnetic field at the electroweak scale could be strong (of order 1017 Gauss). Therefore, at this scale, the effects of the spin flavor precession could not be negligible. Using present limit on neutrino magnetic moments, we show that the lepton asymmetry may be reduced by 50% due to the spin flavor precession induced by strong primordial magnetic fields. In addition, the leptogenesis will have different feature from the standard scenario of leptogenesis, where the lepton asymmetry continues to oscillate even after the electroweak phase transition.