  We study the model with three right-handed neutrinos which masses are smaller
than the weak scale ${\cal O}(10^2)$ GeV (called as the $\nu$MSM). The model
can explain the origin of neutrino masses by the seesaw mechanism, offer a
candidate of dark matter and realize the baryogenesis via neutrino oscillation.
The seesaw mechanism at such energy scales can induce phenomenon which are
observable by experiments. As an example, we discuss the lepton universality of
charged kaon decays in this model. It is shown that the heavy neutral leptons
accounting for the neutrino masses and the cosmic baryon asymmetry can give a
significant correction to the lepton universality, and that the deviation from
the Standard Model prediction can be large as ${\cal O}(10^{-3})$ which will be
probed by near future experiments.
