  The axino, the fermionic superpartner of the axion, is a well-motivated
candidate for cold dark matter if it is the lightest supersymmetric particle.
Since the axino couples very weakly to the matter multiplets, the
next-to-lightest supersymmetric particle (NLSP) has a long lifetime, which has
important consequences for both cosmology and collider phenomenology. Assuming
that a charged slepton is the NLSP, we calculate the complete leading one- and
two-loop contributions to its decay. We analyze in detail constraints on the
parameters space from cosmology and discuss how this scenario can be probed at
colliders. Scenarios in which both the axino and the gravitino are lighter than
the long-lived charged slepton are also explored with particular emphasis on
cosmological constraints and collider phenomenology.
