Neutrino masses in astroparticle physics

Abstract

The case for small neutrino mass differences from atmospheric and solar neutrino oscillation experiments has become compelling, but leaves the overall neutrino mass scale m ν undetermined. The most restrictive limit of m ν<0.8 eV arises from the 2dF galaxy redshift survey in conjunction with the standard theory of cosmological structure formation. A relation between the hot dark matter fraction and m ν depends on the cosmic number density n ν of neutrinos. If solar neutrino oscillations indeed correspond to the favored large mixing angle MSW solution, then big-bang nucleosynthesis gives us a restrictive limit on all neutrino chemical potentials, removing the previous uncertainty of n ν . Therefore, a possible future measurement of m ν will directly establish the cosmic neutrino mass fraction Ω ν . Cosmological neutrinos with sub-eV masses can play an interesting role for producing the highest-energy cosmic rays ( Z-burst scenario). Sub-eV masses also relate naturally to leptogenesis scenarios of the cosmic baryon asymmetry. Unfortunately, the time-of-flight dispersion of a galactic or local-group supernova neutrino burst is not sensitive in the sub-eV range.