  The axino and the gravitino are extremely weakly interacting candidates for
the lightest supersymmetric particle (LSP). We demonstrate that either of them
could provide the right amount of cold dark matter. Assuming that a charged
slepton is the next-to-lightest supersymmetric particle (NLSP), we discuss how
NLSP decays into the axino/gravitino LSP can provide evidence for
axino/gravitino dark matter at future colliders. We show that these NLSP decays
will allow us to estimate the value of the Peccei-Quinn scale and the axino
mass if the axino is the LSP. In the case of the gravitino LSP, we illustrate
that the gravitino mass can be determined. This is crucial for insights into
the mechanism of supersymmetry breaking and can lead to a microscopic
measurement of the Planck scale.
