# Are neutrinos and sterile neutrinos both dark matter candidates?

Are both neutrinos and sterile neutrinos candidates for dark matter?

In particular, why would "standard" neutrinos be a candidate for dark matter, since they interact with matter?

Why would explicitly sterile neutrinos be needed, since standard neutrinos already interact very weakly?

Why are neutrinos and sterile neutrinos considered as separate dark matter candidates?

• The neutrino might interact but it's the weak interaction only, so it has a very very small chance to occur. Have you heard of WIMPs before? – Triatticus May 1 at 10:34
• @Triatticus : thank you. Yes : I know that WIMP is a candidate for Dark Matter (different to neutrino and different to sterile neutrino). So why do people separate neutrino and sterile neutrino as candidates for dark matter ? – Mathieu Krisztian May 1 at 10:38
• That's the thing DM so far only interacts through gravity, same as the sterile neutrino, it's an attractive candidate to those who support the idea. – Triatticus May 1 at 10:50
• Possible duplicates: physics.stackexchange.com/q/17227/2451 , physics.stackexchange.com/q/158319/2451 and links therein. – Qmechanic Jun 14 at 11:37

From $$\beta\beta$$ decays, we find an upper limit for the density parameter for neutrinos of $$0.02\ll\Omega_\text{DM}$$; therefore, neutrinos can only account for a small part of the total dark matter component.