Even zero mass particles interact with gravity. Anything with energy does.
Having non zero mass means that at least in theory we could slow them down to get a better look at them. But so far we have no idea how, which means that we don't even know what the mass actually is. We just know from the way from the types of neutrinos observed that they can change type, and they couldn't do that if their mass were zero.
> Having non zero mass means that at least in theory we could slow them down to get a better look at them. But so far we have no idea how...
How about cosmic expansion? Of the neutrinos emitted early in the universe, shouldn't most still be around, given how weakly neutrinos interact? And, given how much everything in the early universe is receding from us, shouldn't they be slowed down in our frame of reference? If they were emitted when the universe became transparent to neutrinos, what Z would that correspond to? What velocity would we observe in the local frame of reference? (Does it depend on how close to c their velocity is? Do we know?)
What would we expect the density of such neutrinos to be? Enough that we could observe it? (One "gotcha" is that slower-moving neutrinos might have a smaller interaction profile than fast-moving ones, and so be harder to detect.)
Wikipedia says decoupling was at 1 second after the Big Bang, and that neutrinos from that era have energy of 1e-4 to 1e-6 eV (compared to current neutrinos that may be as much as 0.8 eV).
I don't know any answers here, but this is an awesome question. I too am now super-curious about the Cosmic Neutrino Background.
https://en.wikipedia.org/wiki/Cosmic_neutrino_background
...And I suppose there are probably good reasons for this to be impossible, but wouldn't it be wild if a "mechanism" for things like the "randomness" of beta decay were that a really slow/low energy neutrino from the big bang interacts with a neutron, causing it to decay into a proton, and an electron, and the neutrino gets a boost in energy as well.
Antineutrinos can cause inverse beta decay, so maybe neutrinos can cause inverse fusion?
Edit: apparently it just causes transmutation.
https://en.wikipedia.org/wiki/Homestake_experiment
There are various kinds of neutrino interactions:
https://www.vivaxsolutions.com/physics/feynman-diagrams.aspx
...(scroll down for the nice animated diagrams).
Sorry, I was being brief. I usually say "anything with a non-zero rest mass-energy" for anything for a photon, photons never being at rest. Briefly, some had thought that neutrinos might be little more than floating carriers of lepton number. Later that was amended to merely "massless" (in the sense that they would at least be like photons). I've never been in that crowd. My thoughts are that mass-energy is the coin of existence and gravitation the inevitable consequence, but I do not speak for everyone, just trying to give a kind of non-exhaustive overview of the history to respond to the for part.
Neutrino detectors essentially slow them down - a neutrino hits an electron, transferring momentum, and then the high speed electron gives off Cherenkov radiation.