||Relic abundance in a secluded dark matter scenario with a massive mediator
Okawa, Shohei ,
Tanabashi, MasaharuYamanaka, Masato
023006 , 2017-01 , American Physical Society
The relic abundance of the dark matter (DM) particle d is studied in a secluded DM scenario, in which the d number decreasing process dominantly occurs not through the pair annihilation of d into the standard model particles, but via the dd→mm scattering process with a subsequently decaying mediator particle m. It is pointed out that the cosmologically observed relic abundance of DM can be accomplished even with a massive mediator having a mass mm non-negligibly heavy compared with the DM particle mass md. In the degenerated d−m case (md=mm), the DM relic abundance is realized by adjusting the dd→mm scattering amplitude large enough and by choosing an appropriate mediator particle lifetime. The DM evolution in the early universe exhibits characteristic “terrace” behavior, or two-step number density decreasing behavior, having a “fake” freeze-out at the first step. Based on these observations, a novel possibility of the DM model buildings is introduced in which the mediator particle m is unified with the DM particle d in an approximate dark symmetry multiplet. A pionic DM model is proposed to illustrate this idea in a renormalizable field theory framework.