Neutrino asymmetry around black holes: Neutrinos interact with gravity

Propagation of a fermion in curved space-time generates a gravitational interaction due to coupling of its spin with the space-time curvature connection. This gravitational interaction, which is an axial-four-vector multiplied by a four gravitational vector potential, appears as a CPT violating term in the Lagrangian which generates an opposite sign and thus asymmetry between the left-handed and the right handed partners under the CPT transformation. In the case of neutrinos, this property can generate a neutrino asymmetry in the Universe. If the background metric is of the rotating black hole, i.e. the Kerr geometry, this interaction for the neutrino is non-zero. Therefore, the dispersion energy relations for the neutrino and its anti-neutrino are different which give rise to the difference in their number densities and the neutrino asymmetry in the Universe in addition to the known relic asymmetry.