[dphidt]

The other comments are spot-on. I'll just add that the neutrinos flavors are defined by the way they interact: electron neutrinos interact to produce electrons, never muons. So they're quite different in that sense, and in the current Standard Model of particle physics, they're treated as independent particles. (This is not to say that in the future, we won't require a more comprehensive model that could relate particles in a deeper way.)

We know from experiments like LEP (electron-positron collisions) that there are only three kinds of neutrinos that participate in weak interactions (electron, muon, and tau). Thus the fourth neutrino type suggested by these anomalous oscillation measurements cannot interact via the weak force, meaning it doesn't interact at all,* hence sterile. The only way to detect them is through their influence on the oscillations of other neutrino types.

* They'd still feel gravity, which isn't included in the Standard Model anyway.

[ianai]

Thank you so much for replying! I learned quite a bit.

What is the source of neutrinos in the experiments suggesting sterile nutrinos? Is it different from the non confirmations?