Two-loop Dirac neutrino mass and WIMP dark matter

Abstract

We propose a "scotogenic" mechanism relating small neutrino mass and cosmological dark matter. Neutrinos are Dirac fermions with masses arising only in two--loop order through the sector responsible for dark matter. Two triality symmetries ensure both dark matter stability and strict lepton number conservation at higher orders. A global spontaneously broken U(1) symmetry leads to a physical $Diracon$ that induces invisible Higgs decays which add up to the Higgs to dark matter mode. This enhances sensitivities to spin-independent WIMP dark matter search below $m_h/2$.

Comments: 11 pages, 3 figures; references added, Fig. 3 updated to include recent limits reported by LUX and PandaX. Version to appear in Phys. Lett. B