Axinos as light dark matter

Abstract

We consider the axino, whose mass can be in the 1 - 10 MeV range, as the light dark matter which can explain the recently observed 511 keV γ-ray line emissions from the galactic bulge through its decay. We discuss the cosmological production and constraints for the axino light dark matter. It is shown that the bilinear R-parity violating terms provide an appropriate mixing between the axino and neutrinos so that the light axino decays dominantly to e+e-v. One appealing point of the axino light dark matter is that the same bilinear R-parity violations consistently give both the lifetime of the axino required to explain the observed 511 keV γ-rays and the observed neutrino masses and mixing.