Light Scalar Top Quarks and Dark Matter at the Linear Collider

The MSSM can explain electro-weak symmetry breaking if one scalar top quark (stop) is light. In addition, in this framework, the neutralino is a good dark matter candidate and for small stop-neutralino mass differences Dm £ 30 GeV, co-annihilation plays an important role to match the results from WMAP and SDSS for the relic density in the universe.  In this scenario, the stops mainly decay into charm and neutralino, making its discovery difficult at hadron colliders due to background and trigger limitations.We present results for the discovery reach of the ILC for a DM candidate as low as 0(5GeV) based on a realistic experimental simulation.