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We discuss radiative seesaw models, in which an exact $Z_2times Z_2$ symmetry is imposed. Due to the exact $Z_2times Z_2$ symmetry, neutrino masses are generated at a two-loop level and at least two extra stable electrically neutral particles are predicted. We consider two models: one has a multi-component dark matter system and the other one has a dark radiation in addition to a dark matter. In the multi-component dark matter system, non-standard dark matter annihilation processes exist. We find that they play important roles in determining the relic abundance and also responsible for the monochromatic neutrino lines resulting from the dark matter annihilation process. In the model with the dark radiation, the structure of the Yukawa coupling is considerably constrained and gives an interesting relationship among cosmology, lepton flavor violating decay of the charged leptons and the decay of the inert Higgs bosons.
The singlet majoron model of seesaw neutrino mass is appended by one dark Majorana fermion singlet $chi$ with $L=2$ and one dark complex scalar singlet $zeta$ with $L=1$. This simple setup allows $chi$ to obtain a small radiative mass anchored by the
We propose two possibilities to explain an excess of electron/positron flux around 1.4 TeV recently reported by Dark Matter Explore (DAMPE) in the framework of radiative seesaw models where one of them provides a fermionic dark matter candidate, and
We study a radiative inverse seesaw model with local B-L symmetry, in which we extend the neutrino mass structure that is generated through a kind of inverse seesaw framework to the more generic one than our previous work. We focus on a real part of
We study phenomenological implications of a radiative inverse seesaw dark matter model. In this model, because neutrino masses are generated at two loop level with inverse seesaw, the new physics mass scale can be as low as a few hundred GeV and the
We discuss the possibility to find an upper bound on the seesaw scale using the cosmological bound on the cold dark matter relic density. We investigate a simple relation between the origin of neutrino masses and the properties of a dark matter candi