Discrete dark matter with light Dirac neutrinos

We propose a new realization of light Dirac neutrino mass and dark matter (DM) within the framework of a non-Abelian discrete flavor symmetry based on A4 group. In addition to A4, we also consider a Z2 and an unbroken global lepton number symmetry U(1)L to keep unwanted terms away while guaranteeing the Dirac nature of light neutrinos. The field content, their transformations, and flavon vacuum alignments are chosen in such a way that the type-I Dirac seesaw generates only one light Dirac neutrino mass while the other two masses arise from scotogenic contributions at one-loop. This leads to the Dirac scoto-seesaw framework, a generalization of the widely studied scoto-seesaw model to Dirac neutrinos. The symmetry breaking of A4 leaves a remnant Z2 symmetry responsible for stabilizing DM. Dirac nature of light neutrinos introduces additional relativistic degrees of freedom ΔNeff within reach of cosmic microwave background experiments. Published by the American Physical Society 2025