Example of weak interactions induced by mixing

Question

I understand that weak interactions are the exchange of W and Z bosons between leptons and quarks (as explained in this other question: Weak Interaction), but when I read Light Sterile Neutrinos: A White Paper it stated that:

A sterile neutrino is a neutral lepton with no ordinary weak interaction except those induced by mixing.

What other types of interaction are there if not the mixing of particles? Or is this not the meaning of mixing? Could you give me an example of such a mixing interaction?

Answer 1

What other types of interaction are there if not the mixing of particles?

If sterile neutrinos do not mix with active (normal) neutrinos, they have only gravity interaction.

Could you give me an example of such a mixing interaction?

If sterile neutrinos mix with electron neutrinos, there is a very small chance a sterile neutrino produces an electron in a neutrino detector.

Answer 2

Only 90% certain, but I would understand it in the sense of neutrino mixing as in e.g. https://arxiv.org/pdf/hep-ph/0310238.pdf leading to neutrino oscillations. So if the sterile neutrino would 'mix' with the other non-sterile ones, it still could interact weakly in that way. Because it cannot remain purely sterile. But on its own it has no coupling to W/Z.