Probing Baryon Asymmetry of the Universe by Using Lepton Universality

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.