Axino as cold dark matter candidate

The possibility of the CDM axino is presented. From the early days of supersymmetry, axino has been considered as hot dark matter and warm dark matter. But the CDM axino has been considered quite recently. It is because the low reheating temperature of the universe is gaining momentum recently from various considerations in particle cosmology. I present a general introduction on the CDM's, in particular the axino, the calculation on the axino density in the universe, and the constraints imposed on the axino parameters.