COSMOLOGICAL IMPLICATIONS OF AXINOS

Axinos are the supersymmetric partners of axions. They arise in models incorporating both low-energy supersymmetry and the axion solution of the strong CP problem. In the present state of knowledge several of the key properties of axinos, which control their cosmological consequences, are poorly determined. But generically there are very significant cosmological consequences, and we attempt to survey the possibilities here. In a wide variety of models the axino is the lightest R-odd particle, and destabilizes the more conventional candidates for this title (photino. higgsino,...) on cosmological time scales. While this consideration perhaps casts some shadow over an important class of dark matter candidates, it turns out that in a large class of models the axino itself becomes a plausible dark matter candidate. In other models the axino is heavy, and unstable. Even then axinos are of cosmological interest, because their decay can be the dominant mechanism for production of the lightest R-odd particle.