We don't know the identity of the particle or particles that constitute the 80% of the mass of the Universe that we have seen gravitationally but not through other interactions. It is possible that dark matter is an elementary particle. read more
It is possible that dark matter is an elementary particle. The majority of physicists would likely say that a single elementary particle is the most likely possibility. This mostly boils down to Occam's razor. It is possible that dark matter is a composite particle which is composed of more elementary particles. read more
Collisionless dark-matter particles do not substantially interact with each other, and therefore do not settle down into compact structures equivalent to stars and planets. Since dark matter does not (by definition) emit light, the evidence for it comes from its gravitational effects: unseen material seems to have influenced the formation, rotation and motions of galaxies. read more
Well, according to my knowledge, particles of dark matter are supposed to be heavy. One proposed candidate for dark matter is WIMP (weekly interacting MASSIVE particle). But neutrinos are the opposite, they have negligible mass, much much smaller than the electron (lightest particle in SM). read more