The Solar Neutrino “Problem”
If you think
you have the solar model down, you can
predict how many neutrinos should be coming out
per second. They are very hard, but not
impossible, to catch. All experiments
show about 1/3 of the predicted neutrinos. In
a triumph for astrophysics, this is
now thought to be caused by neutrino
decay, rather than a bad stellar model
(thus prompting new physics).