BBN limits on extra radiation by cosmic neutrino asymmetries
by
Srdjan Sarikas(Napoli University)
→
Europe/Berlin
313 (Seminar room)
313
Seminar room
MPI für Physik
Description
I will discuss the evolution of neutrino-antineutrino asymmetries in the early universe, particularly in the epoch of Big Bang Nucleosynthesis (BBN), and the emerging bounds on neutrino physics.
It was commonly believed that neutrino oscillations leave no room for a large pre-BBN neutrino degeneracy. On the other hand, the measured primordial helium abundance mildly favors extra radiation, corresponding to the equivalent of $\Delta N_{\rm eff} \sim 1$ neutrino species. We explore if this effect could be explained in terms of a primordial neutrino asymmetry without invoking new forms of radiation. We find that the combined effect of neutrino oscillations, neutrino asymmetries and decoupling allows for some additional radiation, but the maximum contribution of neutrinos is constrained by $N_{\rm eff} <3.5$ for vanishing $\theta_{13}$ and more restrictive otherwise. The Planck satellite will soon fix $N_{\rm eff}$ with high precision. In combination with our results, this measurement may lead to important conclusions about neutrino physics and physics beyond the standard model.