George Fuller
UCSD

Title: "Oh No! Not Sterile Neutrinos!"

Abstract: Here we will discuss the implications of the revolution in  
neutrino physics for astrophysics and cosmology. We have directly  
detected two kinds of "active" neutrinos, electron and muon type, and  
we indirectly infer a third kind, the tau neutrino. The  
Superkamiokande experiment has recently given us good evidence that  
some of these neutrinos likely have nonzero rest masses. However,  
when this result is combined with other hints of neutrino mass from  
solar neutrino observations and the Los Alamos LSND experiment we  
seem to require a fourth kind of neutrino. This neutrino necessarily  
must be "sterile," in that its interactions would have to be far  
weaker than those of ordinary active neutrinos. Light sterile  
neutrinos are not only a challenge to particle physics, but they  
could have dramatic effects in astrophysics. Our pictures for the  
synthesis of the lightest elements in the Big Bang and the heaviest  
elements in supernova explosions could be changed. Furthermore, our  
long cherished constraints on neutrino dark matter would be  
shattered.