Neutrinos in Cosmology

por Georg Raffelt (Max-Planck-Institut fuer Physik)

miércoles 8 may. 2002 18:00 → 19:00 Europe/Madrid

Sala Seminarios IFIC (Edf. Institutos de Investigación)

We review the role of massive neutrinos in cosmology. At present the most restrictive limits on the overall neutrino mass scale comes from cosmological structure formation arguments in conjunction with large-scale galaxy surveys. Conversely, the cosmic neutrino mass density can be constrained by laboratory measurements of the neutrino mass, for example in the KATRIN experiment, if the cosmic number density of neutrinos were known. However, it depends on the unknown cosmic neutrino degeneracy parameters. We show that neutrino oscillations effectively lead to chemical equilibrium before big-bang nucleosynthesis (BBN) if the favored LMA solution of the solar neutrino problem applies. It is supported by the recent SNO results. In this case the restrictive BBN limit on the chemical potential of the electron neutrino applies to all flavors and the cosmic neutrino density is tightly constrained to be within 1% of its standard value. The primordial neutrino oscillations involve fascinating non-linear effects due to the neutrino self-potential which lead to a synchronization of the oscillations of different modes. It is fascinating that solving the solar neutrino problem with the LMA solution indirectly provides a number count of the cosmic neutrino sea. We finally also mention leptogenesis as an important cosmological role for Majorana neutrino masses in the experimentally favored regime.