keV sterile neutrino with large mixing angle is still alive

We study production of keV scale sterile neutrinos with large mixing with the Standard Model sector. Conventional mechanism of sterile neutrino generation in the early Universe leads to overproduction of the Dark Matter and strong X-ray signal from sterile neutrino decay. It makes anticipated ground based experiments on direct searches of sterile-active mixing unfeasible. We argue that for models with a hidden sector coupled to the sterile neutrinos cosmological and astrophysical constraints can be significantly alleviated. In developed scenario a phase transition in the hidden sector modifies the standard oscillation picture and leads to significantly larger mixing angles, thus opening new perspectives for future neutrino experiments such as Troitsk #nu#-mass and KATRIN. This work was made in collaboration with Fedor Bezrukov and Dmitry Gorbunov. (author)