We study a pseudoscalar dark-matter model arising from a complex singlet extension of the standard model (SM), and show that the dark-matter nucleon scattering is suppressed when two C P -even scalars are degenerate. In such a degenerate-scalar scenario we explore the model parameter space which satisfies constraints from the direct detection experiments and the relic density of dark matter. In addition, we discuss a possibility to verify such a scenario by using the recoil-mass technique at the International Linear Collider. We find that a pair of states separated by 0.2?GeV can be distinguished from the single SM-like Higgs state at 5 σ with an integrated luminosity of 2 ? ? ab ? 1 .
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