Scotogenic Cobimaximal Dirac Neutrino Mixing from $Δ(27)$ and $U(1)_χ$

Abstract: In the context of $SU(3)C \times SU(2)_L \times U(1)_Y \times U(1)\chi$, where $U(1)\chi$ comes from $SO(10) \to SU(5) \times U(1)\chi$, supplemented by the non-Abelian discrete $\Delta(27)$ symmetry for three lepton families, Dirac neutrino masses and their mixing are radiatively generated through dark matter. The gauge $U(1)\chi$ symmetry is broken spontaneously. The discrete $\Delta(27)$ symmetry is broken softly and spontaneously. Together, they result in two residual symmetries, a global $U(1)_L$ lepton number and a dark symmetry, which may be $Z_2$, $Z_3$, or $U(1)_D$ depending on what scalar breaks $U(1)\chi$. Cobimaximal neutrino mixing, i.e. $\theta_{13} \neq 0$, $\theta_{23} = \pi/4$, and $\delta_{CP} = \pm \pi/2$, may also be obtained.