Dirac right-handed sneutrino dark matter and its signature in the gamma-ray lines

We show that a Dirac right-handed scalar neutrino can be dark matter (DM) as a weakly interacting massive particle in the neutrinophilic Higgs model. When the additional Higgs fields couple only to the leptonic sector through neutrino Yukawa couplings, the right number of relic density of DM can be obtained from thermal freeze-out of the DM annihilation into charged leptons and neutrinos. At present epoch, this tree-level annihilation into fermions is suppressed by the velocity of DM, and the one-loop annihilation cross section into gamma gamma can be dominant because relevant coupling constants are different. Hence, the recently observed (tentative) gamma-ray line signal in the Fermi-Large Area Telescope can be naturally explained by the annihilation of right-handed sneutrino DM.