Radiative type-I seesaw model with dark matter via U(1)_{B-L} gauge   symmetry breaking at future linear colliders
  We discuss phenomenology of the radiative seesaw model in which spontaneous breaking of the U(1)$_{B-L}$ gauge symmetry at the TeV scale gives the common origin for masses of neutrinos and dark matter (Kanemura et al., 2012). In this model, the stability of dark matter is realized by the global U(1)$_{DM}$ symmetry which arises by the B$-$L charge assignment. Right-handed neutrinos obtain TeV scale Majorana masses at the tree level. Dirac masses of neutrinos are generated via one-loop diagrams. Consequently, tiny neutrino masses are generated at the two-loop level by the seesaw mechanism. This model gives characteristic predictions, such as light decayable right-handed neutrinos, Dirac fermion dark matter and an extra heavy vector boson. These new particles would be accessible at collider experiments because their masses are at the TeV scale. The U(1)$_{B-L}$ vector boson may be found at the LHC, while the other new particles could only be tested at future linear colliders. We find that the dark matter can be observed at a linear collider with $\sqrt{s}$=500 GeV and that light right-handed neutrinos can also be probed with $\sqrt{s}$=1 TeV. 
Shinya Kanemura, Takehiro Nabeshima, Hiroaki Sugiyama
hep-ph