Friday, February 7 , 2003, 16:00
WHGA Auditorium
Dr. G. Raffelt, MPI Munich;
Abstract:
The case for small neutrino mass differences from atmospheric and
solar neutrino oscillations has become compelling, but leaves the
overall neutrino mass scale m_nu undetermined. The most restrictive
limit of m_nu < 0.8 eV arises from the 2dF galaxy redshift survey in
conjunction with the standard theory of cosmological structure
formation. The connection between the cosmic hot dark matter fraction
and neutrino masses depends on the cosmic neutrino density that can be
very large, depending on the unknown values of the neutrino chemical
potentials. However, because the LMA solar oscillation solution
obtains, all neutrino chemical potentials are equilibrated before
big-bang nucleosynthesis, removing the previous uncertainty on the
number density. Cosmological neutrinos with sub-eV masses can play an
interesting role for producing the highest-energy cosmic rays (Z-burst
scenario). Moreover, sub-eV masses relate naturally to leptogenesis
scenarios of the cosmic baryon asymmetry and may thus play a crucial
cosmological role, although probably not for the dark matter problem.