Multi-component dark matter systems and their observation prospects

The dark matter (DM) sector does not have to consist of only one stable particle. In a multi-component DM sector, processes such as the conversion and semi-annihilation of DM particles are allowed in addition to the standard annihilation. We discuss these non-standard processes in a three-component DM system and find that the relic abundance of DM can be very sensitive to them, a fact that has been recently found for two-component DM systems. To consider a concrete model of a three-component DM system, we extend the radiative seesaw model of Ma by a Majorana fermion and a real scalar boson. The inert Higgs boson and the two new particles are assumed to be DM. The semi-annihilation process in this model produces monochromatic neutrinos, and we estimate the observation rate of these neutrinos from the Sun at IceCube. We find that observations of such high energy monochromatic neutrinos from the Sun may indicate a multi-component DM system.