TeV-scale seesaw model with a loop-induced Dirac mass term and dark matter fromU(1)B−Lgauge symmetry breaking

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We show a TeV-scale seesaw model where Majorana neutrino masses, the dark matter mass, and stability of the dark matter can be all originated from the $U(1{)}_{\mathrm{B}\ensuremath{-}\mathrm{L}}$ gauge symmetry. Dirac mass terms for neutrinos are forbidden at the tree level by $U(1{)}_{\mathrm{B}\ensuremath{-}\mathrm{L}}$, and they are induced at the one-loop level by spontaneous $U(1{)}_{\mathrm{B}\ensuremath{-}\mathrm{L}}$ breaking. The right-handed neutrinos can be naturally at the TeV scale or below because of the induced Dirac mass terms with loop suppression. Such right-handed neutrinos would be discovered at the CERN Large Hadron Collider. On the other hand, stability of the dark matter is guaranteed without introducing an additional ${Z}_{2}$ symmetry by a remaining global $U(1)$ symmetry after the $U(1{)}_{\mathrm{B}\ensuremath{-}\mathrm{L}}$ breaking. A Dirac fermion ${\ensuremath{\Psi}}_{1}$ or a complex neutral scalar ${s}_{1}^{0}$ is the dark matter candidate in this model. Since the dark matter (${\ensuremath{\Psi}}_{1}$ or ${s}_{1}^{0}$) has its own $\mathrm{B}\ensuremath{-}\mathrm{L}$ charge, the invisible decay of the $U(1{)}_{\mathrm{B}\ensuremath{-}\mathrm{L}}$ gauge boson ${Z}^{\ensuremath{'}}$ is enhanced. Experimental constraints on the model are considered, and the collider phenomenology at the LHC as well as future linear colliders is discussed briefly.