  The nearly Minimal Supersymmetric Standard Model (nMSSM) is one of the
promising models of the new physics, since this model can avoid hierarchy
problem, mu problem, cosmological domain wall problem, and tadpole problem
simultaneously. In this thesis, we consider the phenomenology of the nMSSM.
Especially, we focus on the phenomenology of the dark matter and the baryon
asymmetry in the universe generated by the electroweak baryogenesis mechanism.
We find that with high-scale supersymmetry breaking the singlino can obtain a
sizable radiative correction to the singlino mass, which opens a window for the
singlet dark matter scenario with resonant annihilation via the exchange of the
Higgs boson. We also propose a new electroweak baryogenesis scenario in the
nMSSM with additional vector-like multiplets. If the soft supersymmetry
breaking scale is O(10) TeV, these scenarios are compatible with each other and
an observed mass of the Higgs boson, constraints by the electric dipole moments
measurements and the flavor experiments. As a result of these two studies, we
conclude that the nMSSM with a high-scale supersymmetry breaking is valid and
can be probed by the direct direction of the singlino dark matter.
