$\nu_R$ dark matter-philic Higgs for 3.5 keV X-ray signal
  We suggest a new model of 7 keV right-handed neutrino dark matter inspired by a recent observation of 3.5 keV X-ray line signal in the XMM-Newton observatory. It is difficult to derive the tiny masses with a suitable left-right mixing of the neutrino in a framework of ordinary simple type-I seesaw mechanism. We introduce a new Higgs boson, a dark matter-philic Higgs boson, in which the smallness of its vacuum expectation value can be achieved. We investigate suitable parameter regions where the observed dark matter properties are satisfied. We find that the vacuum expectation value of dark matter-philic Higgs boson should be about 0.17 GeV. 
Naoyuki Haba, Hiroyuki Ishida and Ryo Takahashi
hep-ph astro-ph.HE hep-ex