Constraints on primordial lepton asymmetries with full neutrino transport

Understand

Primordial neutrino-antineutrino asymmetries can be constrained through big-bang nucleosynthesis (BBN) relic abundances and cosmic microwave background (CMB) anisotropies, both observables being sensitive to neutrino properties.

• The latter constraint, which is due to gravitational effects from all neutrino flavors, is very minute since it is at least quadratic in the asymmetries.
• On the contrary, the constraints from primordial abundances presently dominate, although these abundances are almost only sensitive to the electron flavor asymmetry.
• It is generally assumed that neutrino asymmetries are sufficiently averaged by flavor oscillations prior to BBN, which allows one to constrain a common primordial neutrino asymmetry at the epoch of BBN.