[empyrrhicist]

I mean, we already know about existing "dark" matter particles. The Neutrino comes to mind, though it's not massive enough to explain the gravitational phenomena. LCDM really isn't that weird or unexpected, since it's a lot like what we already observe, and we already think more particles should exist.

[denton-scratch]

Hypothetical "dark matter" doesn't interact with ordinary matter, except gravitationally. Neutrinos do interact with ordinary matter; otherwise we wouldn't be able to build neutrino detectors. Therefore neutrinos are not an example of dark matter.

[consilient]

> "dark matter" doesn't interact with ordinary matter, except gravitationally.

It's possible that this is the case, but particles that also interact with the weak force (hence WIMPs: weakly interacting massive particles) are generally considered better candidates.

[arbitrage]

Neutrinos aren't dark matter.

[mr_mitm]

They are, because they have mass and don't interact electromagnetically. They are just not cold dark matter, because their mass is so low they behave more like radiation than matter, i.e. the scale as a^4 instead of a^3, where a is the scale factor. A sterile neutrino, if it existed, could still be a dark matter candidate.