co-annihilation scenario consistent with relic density and EW baryogenesis, see next section. With small mass difference, the stop decays into neutralino and charm making the analysis very demanding. Nevertheless, it was shown that with the linear collider the region of co-annihilation down to mass differences $\sim {\cal{O}}$(5 GeV) can be covered, fig. \[fig:exp\](c), and the parameters can be determined accurately enough to reach precisions for the dark matter predictions comparable to that from direct WMAP measurements [@milstene]. Additional improvement in the analysis of this scenario can be obtained if charm triggering were available [@nowak].

Cosmology connection
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Understanding the nature of dark matter is one of the most important challenges of both particle and astroparticle physics, and collider experiments may prove useful tool in solving the dark matter puzzle. Among many scenarios, weakly interacting massive particles (WIMPs), with masses and interaction cross sections characterized by the weak scale, are very compelling and WIMPs appear naturally in low energy supersymmetry models with $R$-parity. In contrast, the origin of the matter-antimatter asymmetry is more uncertain. Electroweak baryogenesis provides a possible scenario that relies only on weak scale physics in which the lightest stop mass must be smaller than the top quark mass 