  The precision determination of scalar top quark properties will play an
important role at a future International Linear Collider (ILC). Recent and
ongoing studies are discussed for different experimental topologies in the
detector. First results are presented for small mass differences between the
scalar top and neutralino masses. This corresponds to a small expected visible
energy in the detector. An ILC will be a unique accelerator to explore this
scenario. In addition to finding the existence of light stop quarks, the
precise measurement of their properties is crucial for testing their impact on
the dark matter relic abundance and the mechanism of electroweak baryogenesis.
Significant sensitivity for mass differences down to 5 GeV are obtained. The
simulation is based on a fast and realistic detector simulation. A vertex
detector concept of the Linear Collider Flavor Identification
(LCFI)collaboration, which studies pixel detectors for heavy quark flavour
identification, is implemented in the simulations for c-quark tagging. The
study extends simulations for large mass differences (large visible energy) for
which aspects of different detector simulations, the vertex detector design,
and different methods for the determination of the scalar top mass are
discussed. Based on the detailed simulations we study the uncertainties for the
dark matter density predictions and their estimated uncertainties from various
sources. In the region of parameters where stop-neutralino co-annihilation
leads to a value of the relic density consistent with experimental results, as
precisely determined by the Wilkinson Microwave Anisotropy Probe (WMAP), the
stop-neutralino mass difference is small and the ILC will be able to explore
this region efficiently.
