text: can be achieved only when the annihilation processes are enhanced by Higgs resonances. 
  
  Therefore, the mass of the RH neutrino DM should be around a half of Higgs boson masses. 
  
  We have also calculated the elastic scattering cross section between the DM particle and a 
  
  proton and found it within the reach of future experiments for the direct DM search. 