Relic abundance of dark matter in universal extra dimension models with right-handed neutrinos

Understand

Relic abundance of dark matter is investigated in the framework of universal extra dimension models with right-handed neutrinos.

• These models are free from the serious Kaluza-Klein (KK) graviton problem that the original universal extra dimension model has.
• The first KK particle of the right-handed neutrino is a candidate for dark matter in this framework, and its relic abundance is determined by three processes, (1) the decay of the KK photon into the first KK right-handed neutrino in the late universe, (2) production of the first KK right-handed neutrino from the thermal bath in the early universe, and (3) the decay of higher KK right-handed neutrinos into the first KK right-handed neutrino in the late universe.
• When ordinary neutrino masses are large enough such as the degenerate mass spectrum case, the last process contribute to the abundance significantly, even if the reheating temperature is low.