Hiding an elephant: heavy sterile neutrino with large mixing angle does not contradict cosmology

Understand

We study a model of a keV-scale sterile neutrino with a relatively large mixing with the Standard Model sector.

• Usual considerations predict active generation of such particles in the early Universe, which leads to constraints from the total Dark Matter density and absence of X-ray signal from sterile neutrino decay.
• These bounds together may deem any attempt of creation of the keV scale sterile neutrino in the laboratory unfeasible.
• We argue that for models with a hidden sector coupled to the sterile neutrino these bounds can be evaded, opening new perspectives for the direct studies at neutrino experiments such as Troitsk $\nu$-mass and KATRIN.